Author Topic: Need help identifying component  (Read 193 times)

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Offline zzattack

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Need help identifying component
« on: October 27, 2019, 09:54:59 pm »
I'm looking to replace a SOIC8 chip on a seemingly simple device. The purpose of the device isn't known but given the available info I think it should be easy enough. This is what I traced out:

Code: [Select]
PIN 1: to MCU, pulled up     PIN 8: to MCU, no pull up
PIN 2: external              PIN 7: GND
PIN 3: external              PIN 6: +3v3
PIN 4: +3v3                  PIN 5: to MCU, no pullup

First of all, the orientation is not clear. It could be rotated 180°. Assuming my marking above is not rotated:

* A total of 3 pins are connected to a microcontroller, of which only one is pulled up.
* Pins 2 and 3 lead to a connector through a series resistor. Likely inputs.
* There's a decoupling cap over pins 6 and 7.
The chip's marking definitely has a TI logo and seems to start with '23', possibly 234. Initial suspect is a OPA234x dual opamp, but none of the listed TI opamps seem to conform with this pin organization.

Anyone recognize likely candidates?
 

Offline DaJMasta

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Re: Need help identifying component
« Reply #1 on: October 27, 2019, 10:13:49 pm »
A picture may be helpful, as would values of the resistors.  If you've got a single 3.3V rail and a normal value pullup resistor, I'd expect it's communicating through serial, which rules out analog-only parts like opamps.  You can check this by looking at the micro's datasheet and seeing whether the pins it connects on are hardware serial pins or not - also if they are shared with other devices (an SPI connection, for example, would use three MCU pins, maybe using a pullup on the data pin if the chip in question needs it, and then pin 4 could be chip select.)

I think the real telling thing would be knowing what it connects to, though.  If the series resistors are high value, you can basically guarantee it's an input, but if they're smaller, they could be current limiting protection resistors for the unknown chip.  If they're very low, they could even be a serial transmission line (like USB) that needs them for normal termination, though this also usually involves a ground connection and some small filtering caps and a TVS diode/pair.



Even position on the board or trace thickness can be useful information - in an all digital area of a dual domain board would suggest a digital part, thick power traces or output traces could suggest a driver IC.
 
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Offline fzabkar

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Re: Need help identifying component
« Reply #2 on: October 27, 2019, 10:25:39 pm »
 
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Offline zzattack

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Re: Need help identifying component
« Reply #3 on: October 27, 2019, 11:31:18 pm »
It looks tantalisingly similar to this CAN bus transceiver, but with mirrored pinout:

www.ti.com/lit/ds/symlink/sn65hvd234-q1.pdf

Spot on. Looks like my tracing was done on a mirrored picture. CAN RX/TX match up with remappable pins on the MCU which can be selected for CAN mode and the 234 from the chip marking recurring in the chip type is awfully suspect. Case closed, thank you.
 


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