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TS3A24157: Design Check, SPST to SPDT signal loop controlled

Steve Feng
Prodigy 20 points
Part Number: TS3A24157

Tool/software:

Hi TI, This is Steve

I need to control a system which include SBC (single board computer) and battery

1.

The battery have a spst switch, after measurement

This spst, one contact is pull up 4V with 300K ohm and the other one is connect with GND

I think the MCU inside the battery is sensing this pin to trigger the external GPIO interrupt to turn on/off the power (VDB is 4V~5V)

2.

The SBC have the operating system

3.

The SBC power source is from battery, push the battery spst to turn on the power, and push again to turn off the power,

Because of the point 2 said, the OS is include in SBC, so turn off the power directly will make damage for the SBC.
I have a idea, but I'm not sure this is correct or not

The step is shown as below:

a.Separate the SPST to SPDT,turn the circuit as below, (the switch is shared but the route-trip path are different) VDDs

b.Before battery turn on, the circuit path takes the SPDT's NC, so the user push the switch button, the battery will turn on.

circuit path route: Vgpio3->NC1->COM1->SW->COM2->NC2->DGND

c.After battery turn on, the circuit path takes the SPDT's NO, so the user push the switch button, the battery power will not turned off.

circuit path route: Vdd5V->NO1->COM1->SW->COM2->NO2->R75(MCU will sensing if the switch is push or not)->DGND

remark: make sure R75 value is correct or not, the voltage need to bigger  than MCU's Vih.

d.According these three point mention above, relay could be used, so I found the IC "TS3A24157"

e. the full design file is shown as below, is there I need to modify?

SPSTtoSPDT_Battery.pdf

  • +1
    TI__Mastermind 25893 points

    Hey Steve,

    The circuit looks fine on the NC side (after battery turn on) and from a functional standpoint will work as you're intending on the mux side. I'm concerned on the Vgio3 input (before the battery is turned on). I may be misunderstanding here so I want to confirm by it looks like you're connecting the Vgpio3 voltage directly through a 0ohm resistor, through both the muxes and straight to ground. The current there would be very high and likely damage the switches. Am I understanding that properly? Can you the 0ohm be increased to limit the current to at most 300mA. Shouldn't need much there, maybe just a 1k will be fine.  

    On the NC inputs side (this would be after the batter is turned on), I wouldn't modify anything but like you noted, maybe the R75 resistor may need to be modified depending on your MCU input impedance. Right now, I'm seeing about 3.3V on the output. Depending on the MCU VIH level you may want to slightly increase the R75 to increase the voltage there.

    Thanks!
    Rami

  • 0 in reply to Rami Mooti1
    Prodigy 20 points

    Hi, Ti

    Thank you for your reply

    Sorry that I did not explain clear,

    1.The Vgpio3 which is pull up with 370K Ohm in the battery pack, 
    in the picture 1, the R6 and picture 2 R5 is the current limit resistor!

    2.I will revise the resistor value about R75, thank for your advice!