iPhone Tristar Explained

So, your iPhone 5 or newer is no longer charging. Someone replaced the charge port and the battery and it’s still not charging. Until this problem, you’ve kept the phone in a case and it’s never been dropped, submerged in liquid, or otherwise broken. So what gives?
While there are several reasons an iPhone (or any device) can stop charging, we’ll focus on one reason in particular, the so-called Tristar IC. So what is this Tristar IC ? ? In the photos below, you can see just how tiny this microchip is. The micrometer shows it’s 2.2mm wide (x 2.2 mm). In the other photo, the yellow is actually a golf ball and the chip is sitting inside a divot on the ball. On the bottom of the chip are 36 solder connections. 

This microchip is part of the circuit controlling USB functions – including charging. This microchip is delicate and prone to damage by voltage spikes and noisy electrical signals (more on that later). The name, “U2 IC” comes from the tristars board position on the iPhone 5 (first device Apple used the chip in) schematic. IC is an abbreviation for “integrated circuit”, or microchip and U2 happens to be the label assigned to this particular microchip on the schematic, U being the designation for a microchip (D is for diode, R is for resistor, C is for capacitor) and the number 2 is just what happens to be the assigned number from the Apple engineers. There’s also a U3, U4, U5, and more. In other iPhone models, the chip designation changes. On the iPhone 6, it’s U1700 and it’s a different number among iPads. However, most people just call it the “U2 chip”. A more proper name would be Tristar, since that’s what the chip is, no matter it’s schematic label.

So how does this chip go bad, and how do I know if it’s the chip and not something else, like the battery?

While it’s true many things could be affecting the charge-ability of an iPhone 5 or newer, let’s focus on just three things and discuss how to rule 2 of them out. They are, the dock or charge port, the battery, and the Tristar.

We’ll start with the dock. Something many people fail to understand is that unless the external opening most people refer to as the “charge port” is physically damaged or has debris stuck inside, then odds are extremely high that the port is not the problem. Sure there is an exception to every rule, but the law of averages is against you on this. The dock or port is nothing more than a fancy extension of wire from the opening on the outside to the connection on the logic board. The odds of that wire failing are so remote that you can almost always bet against the port being the problem on a non-charging iPhone – IF there is no damage to the opening and pins inside and nothing is stuck against the back wall, such as pocket lint. If you insist on “checking”, just to be sure, don’t waste time removing the old port, simply unplug it from the board and plug a new one on and let it lay loose over the existing port. (please note that this discussion is only for iPhone lightning ports, not the older 30 pin ports or micro USB ports)

Next up, the battery. After the charge port, many people assume the battery has failed. This is also often a false assumption. Yes, batteries do fail and at a much, much higher rate than charge ports. BUT, unless your device is older than 2 years, the odds of the battery being bad are very, very slim. Also, batteries tend to fail over time and not in one day. If someone says, “my phone worked fine yesterday, but today it’s not charging” then you can almost guarantee it’s not the battery and once you’ve ruled out a bad dock connector (charge port), then you can move on to our third possibility, the USB controlling microchip collectively known as the Tristar chip.

But before we do that, please do not attempt to remove an iPhone battery if your sole purpose is to rule out a bad battery. Like the charge port, you can leave the battery installed, but unplug it and move the connector to the side. Lay a known-good battery over the old battery and plug it in, the connector flex is long enough to do this. Pictured below is an example of how to rule out a battery and/or dock problem simply by removing 2 screws, a retaining plate, and 2 connectors. Leave the old battery and dock in the phone. Removing them just to “test” new ones is a waste of time.

So how do you know if it’s the Tristar IC? There really isn’t a sure-fire method of saying, “this is why I know it’s the Tristar “. The diagnosis is made by the signs/symptoms of the problem and ruling out other possibilities (like the battery or dock). A final test I like to do (which is actually the first test I do before even opening the phone) is to plug the phone into a known-good power supply and a USB ammeter. An ammeter will indicate the supply voltage (should be 5 +/- a decimal or so) and if the phone is charging, it’ll show the current draw in amps. For the 5 series iPhones, this should be about 1 amp and the 6 series phones, you may see up to 1.5-2 amps. Current battery levels influence how many amps the device will draw, but basically anything over 0.5 amps means the phone is charging (once a battery nears full charge, current draw is slowed, so a phone at 98% will pull little current compared to a phone at 37%). In the photo below, I have a portapow ammeter plugged into a 5v supply and into the 5S seen in the picture. The ammeter tells me it’s receiving 5.16v from the supply (as expected), but it shows 0 amps (and 0 watts). This tells me the phone is not charging or is fully charged. Since the phone doesn’t power on, I know it’s not the latter.


So based off this one, simple test (using the ammeter), I’ve already formulated an opinion that the Tristar is the problem. The lightning cord plugs into the port as expected for a normal functioning charge port, the pins did not appear to be bent/damaged, and no debris was obstructing the port, so I’ve ruled out a port problem. All I have to do now is unplug the battery and plug a new known-good one on – which I did. The phone powered on, but the ammeter still read 0 current draw. This is a high suspicion for a Tristar problem. 

Once the Tristar IC was changed out, I plugged it back into the ammeter. As you can see from the pic below, the ammeter reports supply voltage at 4.93 with a current draw of 0.97 amps, which equals 4.63 watts – all normal expected values for a properly functioning device. In addition, the lightning bolt has appeared next to the battery level icon.


So what can be done about a failing Tristar IC?

#1 – PREVENTION! As I mentioned at the beginning, the Tristar IC is prone to damage by voltage spikes and noisy electrical signals. Either or both of these can come from cheap charge cords, wall cubes, and/or car chargers and portable batteries.

#2 – If you used a charger or cord that falls into the above mentioned no-no’s, then you’ll need someone qualified to replace the microchip. There are only a few shops around Aus (and world) who are capable of providing this service. A Google search of your area may be helpful, or you can always mail it to us and we can do the repair for you.

More on the prevention side: You can almost guarantee that any charge cords, wall cubes, and car chargers found in service stations and gift shops are cheap knock-offs of Apple’s products or the products of after-market manufacturers licensed by Apple. While it’s difficult to say what the knock-off chargers and power supplies look like, one thing is helpful for guidance – the presence of the Mfi logo (seen below). The MFi program is Apple’s oversight and stamp of approval for 3rd party manufacturers of charge cords and chargers. Participation in the MFi program means your product meets or exceeds Apple’s standards for quality. Using only MFi certified cords/chargers means you’re protecting your phone against Tristar IC damage. If you’re currently using cords bought at a service station or gift shop, I’d consider throwing them away and buying new ones from a reputable supplier of Apple products, such as JB HI FI or Harvey Norman. You don’t need to buy Apple brand cords, just MFi certified cords. Cords/chargers that are Apple certified (MFi) have this logo on them:


If that logo is NOT on the packaging, it is NOT MFi certified and it’s use at your own risk. Variations of the logo or phrase do not count (ie wording that is, “works with…” or “use with…” or “designed for…”).

Source Credit: www.riceisfordinner.com


NXP’s 1610A3 “TRISTAR2” IC (commonly known as “U2”) handles protocol negotiation for the 8 Pin Lightning Port.

The 1610Ax is mostly responsible for detecting what is connected to the device and assigning it the appropriate functions. Technically, the 1610A3 is the 6th revision of the Tristar IC, and is therefore less failure prone than prior versions.

Tristar Function

The 1610A3 Tristar provides 2x power outputs (PP_E75_TO_TRISTAR), for powering external accessories, as well as 2x data pairs which can be assigned to various functions.

Depending on the accessory connected, available functions can be up to 2 of any of the following:

  • MIKEYBUS (Digital Audio Codec Output, eg. iPhone 7> Headphones).
  • ACCESSORY UART (UART/Serial Interface for HIDs ect).
  • SOC USB (USB Communication with CPU when connected to computer, else identifies charger type to determine available current).
  • BB DEBUG USB** (Baseband Debugging USB interface).
  • DEBUG UART** (UART/Serial Debugging for the SOC/CPU).
  • WRT SOC** (UART Interface for Baseband CPU Programming/Debugging).

**Primarily used by manufacturer. (Apple, Foxconn)

Symptoms of Failure

Due to the complexity of the Tristar IC, and the many connections it has, symptoms of failure can vary in each case. Here are some of the most notable ones:

  • Rapid Discharge of Battery.
  • No Charging, or no current draw.
  • No USB connection to computer.
  • “Accessory Unsupported” messages in iOS.
  • Blue Screen of Death (BSOD).
  • Red Screen of Death (RSOD).
  • Kernel Panic/Bootloop.
  • No Digital Audio Output.
  • Failure to work with certain accessories.
  • Error 9, 4005, 4013, 4014 during Update/Restore.
  • Sudden Death (Device has no signs of life at all).


The 1610A3 is backwards compatible with the 1610A2, and 1610A1, and can be used in the following devices:

Apple iPad

  • iPad Mini 2 (U1300)
  • iPad Mini 3 (U1300)
  • iPad Mini 4 (U1300)
  • iPad Air (U6000)
  • iPad Air 2 (U3500)

Apple iPhone

  • iPhone 5C (U2)
  • iPhone 5S (U2)
  • iPhone 6 (U1700)
  • iPhone 6 Plus (U1700)
  • iPhone 6S (U4500)
  • iPhone 6S Plus (U4500)
  • iPhone SE (U4500)

Credit Source: A One Mobiles