Other Parts Discussed in Thread: LM2841
I'm having a problem in my company which I think may be related to a latch-up condition.
The system which I'm debugging is composed of 1 MCU, 2 IO expanders (PCF8574A), LEDs and displays, plus some memories and transceivers.
In some boards, just after the system is powered up, one of the IO expanders draws a lot of current (~ 500 mA at 3.3V) and heats up a lot.
Each one of its 8 outputs is connected to a PMOS. The IO expander itself is not directly connected to any low impedance load.
This IO expander is located close to a buck switching regulator (LM2841). The problem never occurs with the second IO expander, which is farther away from the regulator. This one also is not connected to any low impedance load.
The problem seems random. The greatest part (~70%) of our boards are working fine, in some boards (~20%) it happens intermittently and in some others boards (~10%) the problem happens every power on.
I have already done:
- The INT pin was left unconnected, I've connected it to 3.3V through a 10k resistor.
- Added 100 nF caps close to the IC, on VCC pins.
None of these modifications have solved the problem.
The next thing to try is to insert 10k pull-ups in all the IC outputs. Currently, each output is directly connected to a PMOS, without pull-ups or pull-downs.
I'm suspecting this is a latch-up condition, causing overheating. Has anyone ever seen a situation like this with this part? What have you done to avoid it? Any suggestions?