eMMC Adventures, Episode 1: Building my own 64GB memory card with a $6 eMMC chip

As seen on Hackaday!

There’s always some electronics topic that I end up focusing all my efforts on (at least for a certain time), and that topic is now eMMC NAND Flash memory.

Overview

eMMC (sometimes shown as e.MMC or e-MMC) stands for Embedded MultiMediaCard; some manufacturers create their own name like SanDisk’s iNAND or Hynix’s e-NAND. It’s a very common form of Flash storage in smartphones and tablets, even lower-end laptops. The newer versions of the eMMC standard (4.5, 5.0 and 5.1) have placed greater emphasis on random small-block I/O (IOPS, or Input/Output operations per second; eMMC devices can now provide SSD-like performance (>10 MB/s 4KB read/write) without the higher cost and power consumption of a full SATA- or PCIe-based SSD.

MMC and eMMC storage is closely related to the SD card standard everyone knows today. In fact, SD hosts will often be able to use MMC devices without modification (electrically, they are the same, but software-wise SD has a slightly different feature set; for example SD cards have CPRM copy protection but lack the MMC’s TRIM and Secure Erase commands. The “e” in eMMC refers to the fact that the memory is a BGA chip directly soldered (embedded) to the motherboard (this also prevents it from being easily upgraded without the proper tools and know-how.

When browsing online for some eMMC chips to test out, I found a seller that had was selling 64 GB eMMC modules for $6 Canadian per pop; this comes out to a very nice 9.375 cents per gigabyte (that’s HDD-level pricing right there!). With that in mind, I decided to buy a couple modules and see what I could do with them. A few days later, they arrived in the mail (and the seller was nice enough to send three modules instead of just two; the third module’s solder balls were flattened for some reason).

Toshiba eMMC Module

Toshiba THGBM4G9D8GBAII eMMC 4.41 modules

Toshiba THGBM4G9D8GBAII eMMC 4.41 modules

The Flash memory I used is a Toshiba THGBM4G9D8GBAII. According to a Toshiba NAND part number decoder:

  • TH: Toshiba NAND
  • G: Packaged as IC
  • B: Vcc (Flash power supply) = 3.3 V, VccQ (controller/interface power supply) = 1.8 or 3.3 V
  • M: eMMC device
  • 4: Controller revision 4
  • G9: 64 GB
  • D: MLC NAND Flash
  • 8: Eight stacked dice (eight 8 GB chips)
  • G: 24nm A-type Flash (I’m not sure what A-type means)
  • BA: Lead-free and halogen-free
  • I: Industrial temperature grade (-40 to 85 degrees Celsius)
  • I: 14 x 18 x 1.2 mm BGA package with OSP (Organic Solderability Preservatives)

Given the low, low price of the eMMC chip, I had to make sure that I wasn’t given counterfeit Flash memory (often fake flash would have only 4 or 8 actual GB usable, with most of the address space looping over itself, causing data loss with extended usage). This involved find a way to temporarily connect the eMMC to my computer. I had a USB 2.0 SD/MMC reader on hand as well as a laptop with a native SD host interface, so now all I needed to do was break out the eMMC signals on the BGA package so that I can connect it to the reader.

eMMC Pinout: Your Balls (Aren’t) Showing

(There is no real way to word a subtitle about BGA solder balls that can’t be interpreted in a… dirtier manner. Moving on…)

There are plenty of pinouts for eMMC on the Internet, but they all show the pinout for a top view. Since I’m not soldering the eMMC to a PCB, I need to get a bottom view. I took a pinout diagram from a SMART Modular Technologies eMMC datasheet, rotated it to a landscape view, flipped it vertically, then flipped each row’s text in order to make it readable again. I then copy-pasted this into PowerPoint and traced out the package and ball pinouts. This allowed me to colour-code the different signal and power lines I’ll need to implement, including the data, clock, command and power lines. Curiously enough, one of the ground pins (VssQ, or controller/MMC I/O ground) was not a ground pin like the standard required; because of this, I decided to leave that pin open-circuit. Additionally, there were several pins that were not open-circuit, but did not have a known purpose either (I suspect these were factory test/programming points for the eMMC controller).

Toshiba THGBM4G9D8GBAII eMMC pinout (solder balls facing up)

Toshiba THGBM4G9D8GBAII eMMC pinout (solder balls facing up)

eMMC Reader: Take 1 (Failed!)

For the first reader, I cut open a microSD-to-SD adapter, exposing the eight pins inside. I soldered a cut-up UDMA IDE cable and glued them in place. Despite my careful work, I still melted a hole through the thin plastic shell of the adapter; thankfully this did not affect the adapter’s ability to be plugged in.

I used double-sided foam adhesive tape and a piece of perfboard to create a small “test bed” for the eMMC module. Using some flux, solder wick, and a larger soldering iron tip, I removed all the (lead-free) solder balls on the center of the IC and replaced them with leaded solder bumps to make soldering the tiny 40-gauge magnet wire easier.

After bringing out the minimum wires required (VCC/VCCQ, GND, CLK, CMD, and DAT0 for 1-bit operation), I soldered the wires of my quick SD adapter, and plugged it into the SD card slot of a (very old) Dell Inspiron 9300.

Calling this board’s operation flaky doesn’t do it justice. It would fail to enumerate 9 out of 10 times, and if I even tried to do anything more than read the device capacity, the reader would hang or the eMMC would drop off the SD/MMC bus and show an empty drive in Windows. It was clear I had to do a full memory card “build” before I could verify the usability of the eMMC Flash memory.

eMMC in an SD Card’s Body: Take 1 (Success… half of the time)

I had a 16 MB (yes, megabyte) SD card lying around somewhere, but as usual, I couldn’t find it among all the clutter around my desk and workspace. Instead, I found an old, slow Kingston 2 GB SD card that I felt would be a worthy “sacrifice” since it was an older type that still had a thin PCB inside (most SD cards nowadays are monolithic, which means it’s one solid chunk with a few pads exposed). After opening up the case carefully with an Exacto knife, I wiggled out the old PCB. I desoldered the orignal 2 GB NAND Flash, and began work on breaking the SD card controller from the PCB as it was a chip-on-board design. It took a while, but I was able to ensure that none of the old SD card hardware would interfere with my rebuild.

I removed the eMMC from the board I made previously, and tested the thickness of it to ensure that it would fit inside the SD card case. It did, although the 0402 surface-mount decoupling capacitors I intended to install would cause a few bumps to be visible through the thin plastic SD card casing.

With my eMMC and SD card pinouts on hand, I used a small bead of epoxy to affix the eMMC to the PCB, balls-side up. I used magnet wire to connect the data lines (4 wires for 4-bit operation which is the maximum that the SD standard supports), and used the unused pads on the eMMC as a kind of prototyping space where I could install ceramic capacitors as close to the module as possible. I used a 0.1 µF 0402 size ceramic capacitor across the VDDi (eMMC internal regulator) and a neighouring GND pad. The rest of the power pads were wired in parallel with a few extra 0.1 µF capacitors added. I made use of the existing three 1 µF capacitors on the PCB as both extra decoupling and connection points for VCC and VCCQ. To prevent shorting of the inner CMD and CLK pins, I only removed the enamel coating from the magnet wire at the very end so I could solder them but avoid the issue of shorting those pins against the other signal and power lines. I then soldered these wires to the terminals on the other side of the PCB.

After spending about ten minutes wriggling the PCB into the SD card casing without damaging the wires, I used a multimeter to ensure all the pins were connected (use a multimeter in diode mode, with the positive lead connected to ground – any valid pins should read ~0.5 volts), and also ensured that there were no polarity reversals or shorts on the power pins.

Now… the moment of truth. At this point my USB 2.0 card reader still wasn’t cooperating with me, so I tried the only other ‘fast’ reader I had at the time – an SD to CompactFlash adapter.

To my relief, I finally got a (mostly) usable card. It appears this particular model has been pre-formatted with FAT32. Viewing the MBR in Hard Disk Sentinel shows nothing notable, apart from the fact that it’s pretty blank and is indicative that it wasn’t formatted for use as a PC boot medium.

Things began to fall apart after I tried running speed tests, as the card would hang if it experienced a lot of write activity at once. I suspected this was a power supply-related issue, so I modified my layout to add more capacitance. For good measure, I added 56 ohm termination resistance for the DAT0-4 data lines, using a small resistor network harvested from an old dead MacBook motherboard.

After these modifications, performance was much, much better. Now that the card was usable, I could finally run some speed tests.

eMMC in an SD Card’s Body – This time, with more feeling decoupling!

After adding several 100 nF and 1uF 0402-size ceramic capacitors on the eMMC package, I was able to get a stable card that could be read by (most) SD card readers. As I was rather anxious to get a decent benchmark from the eMMC, I decided to forego the cheaper Amazon Prime route, and go to my local PC parts store to buy a USB 3.0 card reader – the Kingston FCR-HS4.

After placing the eMMC and SD card PCB back into its plastic casing, I was relieved to see that Windows immediately recognized its presence. All I had to do then was open CrystalDiskMark and run the benchmark. Drum roll please…

Toshiba THGBM4G9D8GBAII/064G4A benchmark in CrystalDiskMark

Toshiba THGBM4G9D8GBAII/064G4A benchmark in CrystalDiskMark

Although I was happy to get a usable benchmark score, my belief that all eMMC devices inherently had better 4K random I/O speeds than their SD counterparts was immediately busted. My guess is that random I/O wasn’t considered to be a priority until eMMC 4.5 or 5.0, and my eMMC modules are only version 4.41.

eMMC module listed as version 4.41

eMMC module listed as version 4.41

After the speed test, I ran the card through the popular Flash memory testing tool h2testw to make sure that I was not given a counterfeit device.

H2testw showing flash memory is good

H2testw showing flash memory is good

Excellent – it’s a genuine device. Despite the slower performance than expected, I’m happy that the memory capacity is as it should be.

“eMMC identification and CSD data, please”

As is the case with any USB memory card reader, I cannot access any of the eMMC device information (that is, the CID/Card Information Data and CSD/Card Specific Data registers). I took a spare SSD from my collection and got a quick Windows 10 installation running on one of my laptops that had a native SD host interface.

eMMC identified as Toshiba 064G4A MMC

eMMC identified as Toshiba 064G4A MMC

Interesting. The eMMC identifies itself as a Toshiba 064G4A MMC card. Googling that information brought up literally zero information, so it appears I’m the only one to have found (or published) any information about it. Although eMMCs support some degree of S.M.A.R.T. health reporting like mainstream SSDs and HDDs, no (easily-available) software (for Windows at least) is available to read it.

Linux has the ability to report the CID and CSD data as long as the native SD host interface is used, as opposed to a USB card reader.

CID: 11010030363447344100151344014e00
CSD: d00e00320f5903ffffffffef96400000
date: 04/2011
enhanced_area_offset: 18446744073709551594
erase_size: 8388608
fwrev: 0x0
hwrev: 0x0
manfid: 0x000011
oemid: 0x0100
preferred_erase_size: 8388608
prv: 0x0
raw_rpmb_size_mult: 0x2
rel_sectors: 0x10
serial: 0x15134401

With the help of Gough Lui’s CID and CSD decoders, I was able to gain some more information about the eMMC device, but not too much as the information I was originally interested in was already collected by this point.

Out of the Reader and Back Into the (CF) Adapter

Now that I know what the eMMC is capable of, I decided to try putting it back into my SD-to-CF adapter and doing another benchmark.

eMMC in FC-1307A SD-to-CF adapter. Note the limited performance of this chipset.

eMMC in FC-1307A SD-to-CF adapter. Note the limited performance of this chipset.

This test highlights one of the biggest limitations of the FC1306T/FC1307A chipset that so many adapters use: their performance is limited to a maximum of 25 MB/s per channel. Good thing I purchased that USB 3.0 reader…

Conclusion

This was quite the learning experience. I not only learned that eMMC flash memory does not necessarily have the near-SSD performance that the latest devices offer, but I learned how to “exploit” the unused pads of a BGA device as a sort of “prototype area” for soldering small components onto.

Did I save any money by rolling my own Flash storage device? Absolutely not – given how much time I spent on this, if I paid myself minimum wage ($12 per hour where I live), I could have bought at least three higher-performance 64GB SDXC cards with none of the frustration of trying to adapt an embedded memory device as a removable memory card. But where’s the fun in that? 🙂

Performance analysis/review of Kentli PH5 Li-ion 1.5V AA battery

In my previous blog post, I tore down the Kentli PH5 battery – a Li-ion battery that has an internal 1.5-volt regulator that allows for terrific voltage stability… up to a point. In terms of data collection, so far I have collected 55+ runs of data logs (248 MB of text files!) and still do not quite have all the data I want. As for the data that I do have, I will be disseminating them with as much thoroughness as possible.

Voltage vs. load current

As expected, the voltage output of the PH5 remains quite stable, up until roughly 2.1 amps where the voltage sags noticeably until the regulator goes into overcurrent protection mode.

A maximum load capacity of 2.1 amps seems to be a bit… limiting. That said, I have not done tests on the PH5’s transient load capacity, as it would require more automated control than what I currently have available.

Another issue with having such a flat discharge curve is that any device that performs fuel gauging using voltage alone will report 100% capacity, until it suddenly shuts down. This could be a big problem for digital camera users, as they will have no indication that their batteries are running low, until the device abruptly stops working. If the camera was writing an image to its memory card when the battery died, it could cause the image to be corrupted, or worse, damage the file system on the card!

Voltage vs. state-of-charge

Unless you are running the battery at a high discharge rate, the output voltage will be flat at 1.5 volts before abruptly brickwalling and dropping to zero immediately at the end of discharge. At a high load (in the case of the graph below, at 2 amps), the voltage remains flat until the very end of the discharge cycle (99% depth of discharge for my test run), where it quickly tapers off and drops to zero.

Capacity vs. load

This is the big one, and it took a lot of work to get this data, especially at low loads (48+ hours of continuous logging is just asking for Murphy’s Law to come into play). I used almost 50 discharge runs to create the graph below.

This is where things get… interesting. I was expecting the capacity to peak at low currents then taper off as the load current increases. Instead, I noticed a definite ‘hump’ in capacity around the 250 mA mark (reaching a maximum of 1700 mAh / 2550 mWh), and only after that point did I see the expected downward slope in capacity, reaching 1200 mAh (1800 mWh) at the 2 amp mark.

This data brings forth some very interesting conclusions. The PH5’s capacity is inferior to its Ni-MH counterparts (even the relatively crappy ones), and at higher discharge rates it has similar capacity to that of an alkaline at the same load, albeit with much better voltage stability than the Ni-MH or alkaline chemistries.

Other findings

Although I won’t go into too much detail for the next few points (I haven’t gotten quite enough data to be presentable), there are some other issues with the battery that I think should still be mentioned.

One issue is the amount of heat the battery gives off at high loads. At 2.1 amps, I had to use a fan to blow cool air onto the DC-DC converter just to prevent it from entering its over-temperature shutdown mode. Although the converter itself can tolerate elevated temperatures, the Li-ion cell inside will not; the uneven heating that the cell will encounter could potentially degrade its lifespan in the long run.

Another problem is efficiency. At 1 amp, the DC-DC converter is about 75% efficient, and is only 65% efficient at 2 amps. I have not tested the converter’s efficiency at lower loads yet, but I doubt it will achieve more than 85-90% efficiency.

A potential issue with this battery is self-discharge. The buck converter remains active all the time, unless the converter or the Li-ion protection circuit enters a protective shutdown state. I have not had a chance to fully charge an unmodified battery in order to perform a long-term self-discharge test, but I will create another blog post for that, if/when the time comes.

Conclusion

Overall, I’m on the fence when it comes to this battery. Its innovative design does provide unparalleled voltage stability, but its low capacity even at moderate discharge rates dampens the fun significantly. Additionally, the 2.1 amp discharge limit could prove to be a bottleneck for some high-drain applications; this, coupled with the cell’s tendency to shut down abruptly when the internal cell runs empty could potentially cause file system corruption for digital cameras that have not been designed to handle such sudden power interruptions.

Also, the batteries are very costly. At about $10 per cell, you may want to think twice about replacing all your current disposable and rechargeable batteries with these newfangled Li-ion ones. Don’t forget the charger either, as a special charger is required to make contact with a recessed terminal on the top of the battery.

Overall, this cell is… interesting. Just don’t expect a miracle in a steel can.

Pros:

  • Excellent voltage stability, even at high loads
  • Li-ion chemistry allows for a very lightweight cell, even with the addition of a DC-DC converter
  • High output voltage could allow some devices to run more efficiently

Cons:

  • Low capacity – provides a mere 1200 mAh (1800 mWh) @ 2 amps, and up to 1700 mAh (2550 mWh) @ 250 mA (even alkaline batteries can do better than this)
  • Abrupt shutdown when the battery is overloaded, overheated, or over-discharged
  • Runs hot at high loads (and therefore is fairly inefficient)
  • 1.5 MHz converter and unshielded inductor can cause excessive EMI (electromagnetic interference) in sensitive devices
  • Expensive! Costs approximately $10/cell
  • Requires proprietary charger

Bottom Line: This is a niche product and should not be considered a universal replacement for alkaline or Ni-MH AA batteries.

Ramble: Fixstars’ 6TB SATA SSD – is it a thing?

If you know me personally, you’ll know that I absolutely love SSDs. Every PC I own has one, and I can’t stand to use a computer that runs off an HDD anymore. Naturally, when I read about a 6 TERABYTE SSD coming out, it piqued my curiosity.

Photo is owned by Fixstars and is not my property. Retrieved from http://www.fixstars.com/en/news/wp-content/uploads/2015/05/SSD-6000M.png

Official SSD-6000M promotional photo, taken from Fixstars’ press release

A Japanese company by the name of Fixstar has recently announced the world’s first 6TB SATA-based SSD. Although 2.5″ SSDs in such a capacity range already exist, they’re SAS (Serial Attached SCSI) based which limits them primarily to server/datacenter usage. According to Fixstars’ press release, their SSD-6000M supports sequential read speeds of 540 MB/s, and sequential write speeds of 520 MB/s, which is on par with most modern SATA III (6 Gbps) SSDs on the market today.

Concerns

However, after reading a bit online, I’m beginning to have some concerns about the drive’s real-world performance. One thing that is rather worrying is that the company has only mentioned sequential I/O speeds and has said nothing on random I/O or read/write latency; although SSDs do have much better sequential speeds than their mechanical spinning counterparts, they really shine when it comes to random I/O (which makes up much of a computer’s typical day-to-day usage). In the early, early days of SSDs, manufacturers cared only about sequential I/O and it resulted in some SSDs that were absolutely terrible when it came to random I/O (fun fact: I once had an early SSD, the Patriot PS-100, and its performance was so bad that it actually turned me off of SSDs for a few years, so I know how bad such unoptimized SSDs can perform).

Construction

The SSD appears to be made up of 52 eMMC (embedded MultiMediaCard) chips in a sort of RAID 0 configuration and an FPGA (field-programmable gate array) as the main controller. In layman’s terms, this SSD is literally made up of a bunch of SD cards “strapped” together with a chip so that it appears as one single drive. In that sense, one can make a similar solution using a board like this, which parallels multiple microSD cards to act as a single ‘SSD’.

Image retrieved from Amazon (http://ecx.images-amazon.com/images/I/51y0QqWL5sL.jpg)

The consumer equivalent of the SSD-6000M: SD cards and a controller chip. You can even get them from Amazon.

Conclusion

I’m wary of how well this SSD is going to take off. It could end up being a tremendous success, but it’ll certainly be out of the reach of the consumer market – either by its potentially poor random I/O performance, or its price (apparently it will cost well over $6000 USD).

A Little Pick-Me-Up: Samsung 840 EVO SSD slowdowns, and how to fix it (for now…)

There’s been word going around that Samsung’s 840 EVO solid-state drives have an issue where they become really, really slow to read if the data on it has been sitting around for a few months, and I can confirm this is the case as well.

The first half of the drive (which holds a fair amount of static data) was being read at around 30 MB/s, with newer data being read at almost 500 MB/s. That’s a pretty big difference. One thing to note (I didn’t take a screenshot for this) is that although the overall read speed was significantly affected, the read latency was only somewhat slower; only about 10-20 microseconds of extra latency.

To temporarily fix this (at least until Samsung releases a firmware update in the middle of October), I used Hard Disk Sentinel to read and rewrite all of the data on the SSD. Because this involves accessing data that is normally locked by Windows, I made a custom WinPE (a slimmed-down, portable version of Windows that’s used for installation and recovery) image with Hard Disk Sentinel inside it. This allowed me to boot outside of the normal Windows setup, and perform the Read+Write+Read test to refresh all of the data stored on the SSD. Note that this will impart a lot of write activity to the NAND flash in the SSD (hence a chance for increasing wear), but modern SSDs aren’t as delicate as people might think.

HD Sentinel's Refresh Data Area test

Hard Disk Sentinel’s “Refresh Data Area” test

This took about 2 hours on my 250 GB SSD. Afterwards, another read test showed that the drive was working smoothly again.

Will I still buy a Samsung SSD? Absolutely. No data was lost and Samsung did the right thing by acknowledging the issue and also finding a way to fix it, as opposed to simply calling it a non-issue and sweeping it under the rug.

Looking inside a (fake) iPhone 5S battery

Considering how popular the iPhone is, there’s always going to be some counterfeits out there. I’ve been out buying various iPhone batteries to build a database of each generation’s characteristics, but one model has eluded me so far: the iPhone 5S. The iPhone 5C’s battery that I bought appears to be genuine (but with its own issues), but none of the iPhone 5S batteries I’ve bought so far (4 of them at the time of writing this blog post) were genuine. All of these fakes look like a genuine battery at first glance, but all of them share a few common traits.

Battery teardown

The fake battery sports the usual iPhone battery information, complete with some dot-matrix printed data and a data-matrix barcode. It’s labeled with a capacity of 1560 mAh and 3.8 volts nominal voltage.

Comparison between real and fake iPhone 5S battery

Comparison between real and fake iPhone 5S battery

The connector itself has two points for soldering the connector to provide durability. However, with the fake batteries, they are not soldered down. The two spots on the ends of the connectors are dark with a small point visible inside it (that point is the reinforcement pin on the connector). If this connector is installed in an iPhone, it will probably not come out without either damaging the battery’s connector, or worse, leave the plastic connector piece inside the phone, requiring tweezers to remove.

Connector lifted off with a hobby knife

Connector lifted off with a hobby knife

iPhone 5S and 5C battery pinout

iPhone 5S and 5C battery pinout

Removing the black protective tape reveals an iPhone 4 battery fuel gauge board. The connector is soldered to this board, with four solder points visible.

iPhone 4 battery PCB with soldered-on flat flex connector

iPhone 4 battery PCB with soldered-on flat flex connector

Pulling out the PCB  reveals another characteristic of these fake batteries: the positive terminal is cut short, with another metal section being clumsily spot-welded to the stub on the cell.

Note how the battery tab is poorly welded to the PCB.

Note how the battery tab is poorly welded to the PCB.

Battery fuel gauge data

The battery fuel gauge requires proper programming to accurately indicate the battery’s charge status. Because of this, each iPhone battery generation has its own specific configuration.

The fake iPhone battery retains the programming for the iPhone 4’s battery, which is a designed capacity of 1420 mAh, using a bq27541 fuel gauge running version 1.25 firmware. The data inside it is often that of a used/recycled battery as well.

This data can be (partially) read out directly from the iPhone with a tool such as iBackupBot, but more data can be read if the battery is read with another tool. I have the EV2400 from Texas Instruments to read this out on a PC, but this data can be read out with a USB-to-TTL serial port, a logic gate (a logic inverter) and a small MOSFET transistor.

I created a small tool that uses this circuit to interface with the fuel gauge and read out its data. Check it out here.

Using my tool, this is the report for one of these fake batteries. Note how it is identified as an iPhone 4 battery. Don’t be fooled by the calculated state of health. It’s not accurate for this battery as the fuel gauge still thinks it’s still inside an iPhone 4 battery pack.


**** START OF HDQ BATTERY LOG REPORT ****
HDQ Gas Gauge Readout Tool version 0.9 by Jason Gin
Date: 9/30/2014
Time: 0:52:24
Serial port: COM26

Battery Identification
========================
DEVICE_TYPE = 0x0541, FW_VERSION = 0x0125, DESIGN_CAPACITY = 1420 mAh
Battery's configuration matches that of a standard iPhone 4 battery.

Basic Battery Information
===========================
Device = bq27541 v.1.25, hardware rev. 0x00B5, data-flash rev. 0x0000
Voltage = 3804 mV
Current = 0 mA
Power = 0 mW
State of charge = 45%
Reported state of health = 0%
Calculated state of health = 99.3%
Cycle count = 14 times
Time to empty = N/A (not discharging)
Temperature = 27.9 °C (80.3 °F) (3009 raw)
Designed capacity = 1420 mAh
Heavy load capacity = 628/1410 mAh
Light load capacity = 673/1455 mAh

Advanced Battery Information
==============================
Capacity discharged = 0 mAh
Depth of discharge at last OCV update = ~778 mAh (8768 raw)
Maximum load current = -200 mA
Impedance Track chemistry ID = 0x0163
Reset count = 11 times

Flags = 0x0180
Flag interpretation:
* Fast charging allowed
* Good OCV measurement taken
* Not discharging

Control Status = 0x6219
Control Status interpretation:
* SEALED security state
* SLEEP power mode
* Constant-power gauging
* Qmax update voltage NOT OK (Or in relax mode)
* Impedance Track enabled

Pack Configuration = 0x8931
Pack Configuration interpretation:
* No-load reserve capacity compensation enabled
* IWAKE, RSNS1, RSNS0 = 0x1
* SLEEP mode enabled
* Remaining Capacity is forced to Full Charge Capacity at end of charge
* Temperature sensor: External thermistor

Device name length = 7 bytes
Device name: bq27541

**** END OF HDQ BATTERY LOG REPORT ****

Looking inside an iPhone 5 battery

In the wake of my previous teardowns of the iPhone 4 and 4S batteries, I went onto eBay and Amazon (realizing that they finally have Amazon Prime student rates up in Canada) and bought a few iPhone 5 and 5S batteries. Although I was primarily interested in trying to get the gas gauge information out of the batteries, I had a secondary reason. The Nexxtech Slim Power Bank (a subject of a separate blog post) uses a pair of 3.8-volt Li-ion polymer batteries, and they seemed to be be suspiciously similar in size to what is used in the iPhone 5. But enough of that, we’re here for the iPhone 5 battery in particular!

Battery Casing

The iPhone 5 battery measures 3.7 mm in thickness, 3.2 cm in width and 9.1 cm in length. This particular model, made by Sony, has a model ID of US373291H, with the six digits corresponding to the cell’s dimensions. This cell has a labeled capacity of 1440 mAh at a nominal 3.8 volts, with a maximum charge voltage of 4.3 volts. I tried to read the data matrix barcode on the cell but my barcode scanning app on my phone refused to recognize it. I might try to scan and sharpen the barcode later but it’s not something that’s of a high priority to me.

Battery Teardown and Pinout

The board itself is rather interesting. The protection MOSFETs used to switch the battery’s power are chip-scale packages and are glued down with epoxy, same with the gas gauge itself. This means that I can’t easily replace it with a rework station if the need arises. The board includes the gas gauge, thermistors, protection circuitry and still has room for a polyfuse for extra over-current protection.

iPhone 5 battery PCB layout

iPhone 5 battery PCB layout

The pinout of the iPhone 5 battery is pretty much the same as of the iPhone 4 and 4S. You have Pack-, NTC Thermistor, HDQ and Pack+. In this particular model of battery, the gas gauge is a bq27545 (labeled SN27545), but has basically the same feature set as the iPhone 4/4S’ bq27541. With this information, I soldered to the small terminals on the connector (the actual connectors for this battery haven’t arrived yet since it takes so long to receive items from China on eBay), and hooked it up to my trusty Texas Instruments EV2400 box.

iPhone 5 battery pinout

iPhone 5 battery pinout

Battery Data

iphone 5 firmware versionAnd once again, we’re presented with an obscure firmware revision. The latest bq27545-G1 firmware is only version 2.24, but this chip has version 3.10. After forcing GaugeStudio to accept this gauge as a -G1 version, we’re once again presented with a sealed chip. Let’s try to unseal it with the default key…

... aaaaand nope. No dice with 0x36720414, unlike last time.

Nope. No dice with 0x36720414, unlike last time.

… and I get the dreaded “Unseal Key” prompt. Cue the dramatic Darth Vader “NOOOOO” here. Maybe Apple read my previous post and decided to change the default keys this time (Hey Apple, if you read this, make the iPhone 6’s gas gauge have the default keys again)! This means that not only can I not access any of the juicy details of this battery, but I cannot update its firmware to a more… conventional version either. I could try brute-forcing it, but trying to hack a key with a 32-bit address space over a 7 kbps bus… uh, no. That’s not going to happen. I’d probably have better luck reverse-engineering Apple’s battery code but I doubt they have any facility to do in-system firmware updates for the gas gauge.

Data captured from GaugeStudio

Data captured from GaugeStudio

Now for some rather… interesting details of what we can access. The design capacity of this battery, according to the gas gauge, is 1430 mAh, same as the iPhone 4S and also 100 mAh less than what’s written on the label. That, and the full charge capacity of this battery is 1397 mAh out of the gate. The gauge seems to be an insomniac (it won’t enter Sleep mode even when the battery is not hooked up to any load), and it seems to have less features despite having a higher firmware version (I’m sure the internal temperature isn’t 131 degrees C…), and the Pack Configuration register doesn’t bring up any sensible data.

Battery… conspiracy?

One thing that I haven’t confirmed is whether or not this battery had been tampered with before I received it. I bought this particular battery from eBay and it was listed as new. It had some adhesive residue but no obvious sign of being peeled off from another iPhone. The cycle count is set to 1, and because the gas gauge is sealed, I can’t read any other data like the lifetime data logs. There is a chance that this battery isn’t new and that the seller had somehow changed the data memory and sealed the chip with a non-default key, but I need to wait until some other batteries arrive in the mail and perhaps try reading out batteries taken out directly from some iPhone 5s. Until then, it’s only speculation as to why this chip is sealed with a different key.

The next victims specimens: an iPhone 5S battery, a “new” iPhone 4 battery, and an Amazon Kindle battery.