Help Identifying Part

[Generalquark]

Hi,
 I recently hooked up voltage backwards on something I was working on and smoked this part. I have having trouble finding out what it is. Could one of the component experts help me out? Code is HMBUA Thanks!

[fzabkar]

It's a switchmode step-down converter, but I guess you already knew that.

If we could see the rest of the PCB, perhaps the other ICs might give us a clue. Designers often use the same manufacturer for several ICs.

[amyk]

HM8119A ?

[Generalquark]

That HM8119A could be the correct part. I am not 100 percent sure yet. I took readings on a good one and here is what I got on a DMM. If that is the correct part I am having a hard time tracking down a replacement.
Pin 1 19.45V
Pin 2 0 V
Pin 3 .616
Pin 4 9.71V
Pin 5 19.46V
Pin 6 0V

https://html.alldatasheet.net/html-marking/1245137/HMSEMI/HM8119A/509/2/HM8119A.html

[DavidAlfa]

Probably they used an existing pinout from a common part.
0.8V reference, 45V max input, 500mA output, doesn't seem so strange.
Microchip's MCP16331 seems an exact match, same specs and pinout.
Just do some parametric search: sot23, 6 pin count, and check what's avaliable, ex. RS

[fzabkar]

That HM8119A could be the correct part. I am not 100 percent sure yet. I took readings on a good one and here is what I got on a DMM. If that is the correct part I am having a hard time tracking down a replacement.
Pin 1 19.45V
Pin 2 0 V
Pin 3 .616
Pin 4 9.71V
Pin 5 19.46V
Pin 6 0V

https://html.alldatasheet.net/html-marking/1245137/HMSEMI/HM8119A/509/2/HM8119A.html

It would appear that the "good" device isn't regulating. I would think that the voltage measured at pin#6 would be a little higher than the output voltage. I would measure the voltage on the load side of the inductor.

[Generalquark]

I checked again today with a scope
Pin 1 has a switching pulse to a max of 40.9Vdc
Pin 2 0V
Pin 3 960mv
Pin 4 9.52V steady
Pin 5 19.5V steady
Pin 6 has nothing.

I checked the input to the inductor and it has the 40.9Vdc switching signal on the one side and the other side had around 19.5vdc steady signal. Does this seem correct?

DavidAlfa, I don't have the component substitute experience. Would you say I should be good swapping in the MCP16331? I saw most of the specs seem very close, but the switching frequency was 850 vs 500. That won't cause any issues?

Thanks for all your help guys!

[fzabkar]

I checked again today with a scope
Pin 1 has a switching pulse to a max of 40.9Vdc
Pin 2 0V
Pin 3 960mv
Pin 4 9.52V steady
Pin 5 19.5V steady
Pin 6 has nothing.

I checked the input to the inductor and it has the 40.9Vdc switching signal on the one side and the other side had around 19.5vdc steady signal. Does this seem correct?

It appears that I was wrong. It now looks like the IC is a boost converter. You will probably find a steady 40VDC on the cathode of the Schottky diode ("SF"). Is this the supply for a LED string?


This part (unknown marking) has the correct pinout, but wrong FB voltage (0.6V):

http://hmsemi.com/downfile/HM1535.PDF


This part (wrong marking) has the correct pinout, but wrong FB voltage (0.6V):

http://txsemi.com/Upload/TX9710_V13-10192938183.pdf

[Generalquark]

I checked the Diode marked with Red. 28V stable on the other side. It is not a string of LEDs. There are strings of Asics on the board, but I am unsure how this ic would interact with them.

[DavidAlfa]

Adjust the feedback resistor network, usually only 2 resistors

[fzabkar]

Can you confirm the voltage on pin #3?

Can you tell us what device you are working on? Is it a laptop/netbook/tablet?

[Generalquark]

I'm actually working on a board out of a Asic Crypto Miner.

Checked Pin 3 again with a Scope and DMM

When the board has power but is not enabled
DMM .615Vdc
Oscope 52-54khz signal with the Vmin at .590 and the Vmax at .800 with a small pulse. See capture.

When the board has power and is enabled
DMM .615Vdc
Oscope 41.7khz signal with the Vmin at .590 and the Vmax at .800 with a small pulse. See capture.

Thanks!

[fzabkar]

It looks like 0.6V is the FB voltage. I would measure the frequency of the PWM pulses at the inductor. If it is 1.2MHz, then either of those previous candidates could be a good substitute.

Alternatively, you could search for other subs from ON Semiconductor, Texas Instruments, Monolithic Power, etc. These would be more likely to be stocked by Mouser and Digikey.

[Generalquark]

I'm not following why your looking for 1.2Mhz at the inductor. I just checked the Inductor on both sides. One of the sides is connected to the part, and that one has the pulsed signal. The other side is straight DC. I checked it with the unit powered but not enabled first, then with the unit enabled. On the other side of the inductor voltage is the same in either on or off mode. I'm no good at figuring out which component would be a good fit with this information. Is there a way to know for sure with this information. Thanks Again for persisting with me!

[fzabkar]

The voltage at the output is controlled by pulsing the inductor with a varying duty cycle at a fixed frequency (Pulse Width Modulation, PWM). This frequency influences the selection of the inductor and filter capacitor.

[Generalquark]

I somewhat understand, but not fully. Are you confident which part this is based on the scope captures by chance?