ASSR1510 drops the output of mcu

[rezaf]

Hi, I have many boards that use ASSR1510 in outout of microcontroller for switching battery voltage on and off.

But the behavior of this component is strange. When the MCU drive led of ASSR through bias resistor (560 ohm), the ASSR works Ok but after a short time, the output voltage of MCU start to drop from 4.9v to about 1v and the ASSR go off also the output of ASSR start to drop the voltage.

 

[KlausST]

Hi,

like always: post the schematic.

Klaus

 

[rezaf]

Hi,

like always: post the schematic.

Klaus

 

[KlausST]

Hi,

why an ASSR? You don´t need isolation. But it draws much (battery) input current. The cost is high.

There are dedicated power swtiches. With the features (depends on type) that a power switch needs: low supply current, short circuit proof, dV/dt limit, low ON resistance, maybe even power limit.

The right circuit makes no snese to me. Why paralleled resisitors? Why the high ohmic voltage divider? Why paralleled capacitors? 10pF makes no sense at all. .. At least without additional information.

***

To your problem: Drained out battery? Did you check battery voltage?

Klaus

 

[rezaf]

Excuse me I'm not the designer of this circuit. I know that ASSR is not a good choice and thanks for your complete guide.

The right circuit is pullup circuit for sensing switch push state with ground signal and paralleled resistors is for connecting 12v of battery to pullup circuit.

This assr makes battery voltage available to about 12 pullup circuit for connecting switches to MCU and when the output of MCU starts to drop, the output of assr go off and the MCU see all the inputs as active! and drain out the battery. and this is the fault of circuit.

Now I can't found the cause of droping the output of MCU. The battery voltage and regulator (used for MCU power) output is ok.

 

[KlausST]

Hi,

So you say: VCC of MCU is stable (what value) but port pin voltage goes down. Is this correct?

Do you have a scope to check port pin waveform?

Klaus

 

[rezaf]

Hi,

So you say: VCC of MCU is stable (what value) but port pin voltage goes down. Is this correct?

Do you have a scope to check port pin waveform?

Klaus

Yes Vcc is stable (output of regulator is 5.00, output of MCU pin about 4.9v).
Port pin is stable for about 10 minutes and the start to go down (about 0.01v every second).
Yes I've oscope, I'll check it and give feedback to you.
Note that the PCB is four layer. May be this problem caused by capacitive behavior of mid layers of PCB?

 

[KlausST]

May be this problem caused by capacitive behavior of mid layers of PCB?

No. As long as the MCU supply voltage stays constant.
Measure the MCU GND, VCC and port voltage directly at the IC pin...when the error just happens.

I expect a soldering problem or any other contact problem. I don't think the MCU is the root cause.

A photo could be helpful.

Klaus