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TPS3600: TPS3600 to repalce MAX793 issue

qiang xiang
Intellectual 290 points
Part Number: TPS3600

I persuade my customer to use  TPS3600D33  to replace MAX793.  The schematic is as belows.

But When V330 is  power off , TPS3600 switch over  to the battery (CR2450),  customer found  the battery will run out 

in about two days.   while  MAX793 has no this problem , the battery can run up to  several weeks.

Could you help check if anything wrong about this schematics?   Thank you .

Note:   1.    R419   is   NC

            2.     PIN 6/7/8/9  is unused

            3.  pin  12 is connected with one jumper, but jumper_1  and jumper_2  is not connected. 

                 In other words,  Pin 12 is floating.

  • 0
    TI__Genius 12630 points

    Qiang Xiang,

    I have 3 comments to help.

    #1: TPS3600 has I_battery which is the supply current when operating on the Vbattery of 0.1uA compared to MAX793 which has I_battery of 1uA. This means that if correctly configured, TPS3600 will last approximately 10 times longer than MAX793 when operating on the same battery.

    #2: In the datasheet for TPS3600, the /MR pin does not have any capacitor or resistor connected to that pin like you have in schematic above. The /MR pin is internally pulled up to Vout so there is no need to have external pull-up resistor or capacitor because this will waste additional current. See the block diagram on page 4 of datasheet to see how the /MR pin is internally connected. To see correct /MR configuration see Typical operating circuit on page 1.

    #3: In the datasheet on page 9, it mentions that current can be saved (meaning battery will last longer) if the watchdog input is low for the majority of the watchdog period and then you raise it from "low" to "high" and then back "low" once within 7/8 of the watchdog time-out period to reset the watchdog timer. In the schematic above, you have WDI floating which I don't think is the best approach for driving the WDI pin. Remember to keep watchdog input (WDI) low for 7/8 of the watchdog period then quickly bring high then back low. This is correct watchdog operation for minimum current consumption.

    With these 3 comments, I believe customer made the right decision using TPS3600. Please try to address comment #2 and #3 in order to improve battery life. Please let me know if you have any additional questions or if any additional support is needed. Thanks!

    -Michael