Dears,
Please help to review my circuit, is this right?
TPS3823 WDI is pulled down when power up, but I change a new one in my board, it OK.
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Dears,
Please help to review my circuit, is this right?
TPS3823 WDI is pulled down when power up, but I change a new one in my board, it OK.
Martin,
1) /MR has 52k ohm pull-up resistor to VDD so you do not need R43. You can leave /MR floating or connect directly to power.
2) WDI must be high impedance when not being used to avoid a reset
The circuit looks good. Please let me know if any more support is needed. Thanks!
-Michael
User,
If your probe capacitance is too high when monitoring WDI this could cause the reset. Please disconnect everything from WDI and only monitor RESET on the bad unit and see if RESET triggers.
The only way RESET can trigger when the VDD is good is if something is connected to WDI. WDI must be high impedance (disconnected) or a pulse must arrive on WDI before watchdog timeout. If not using WDI, it must be disconnected.
-Michael
you said my circuit is right,and wo must use WDI.The same circuit, quantity production is no problem before this .so we hope you help us to analyze the bad chip.
Hi Michael,
when WDI is disconnected(remove 0 ohm res connecting to MCU), RST works OK, but it is not what the customer wants.
Hi Michael,
I test the device with the customer again, and post it for your reference.
we use same PCBA for the test.
1, set-up
2, good WDI and RST
3 , Bad WDI and RST
4, besides, we test latch down WDI with 47K ohm Res (R121)as below, the result is:
1) one bad device becomes OK;
2) another bad device still bad;
Martin,
Please remove R121. WDI does not require a pull-down resistor. The CPU (WDI output) must pulse between logic low and logic high or must be set to high impedance.
Also, what purpose is R118? Is there a reason you have a resistor between VDD and 3.3V supply?
-Michael