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TPS35-Q1: original watchdog chip replacement design

shaofei wu
Prodigy 10 points
Part Number: TPS35-Q1
Other Parts Discussed in Thread: TPS35

Tool/software:

Dear all:

our original watch dog IC is S-19400G28A-K8T2U4  ABLIC, we will change it to new  Alternative part is TPS35-Q1 serial ,  full  MPN:TPS35CA**LAEDDFRQ1(** is unknow)

In order to get closer to the original design parameters ， we select TPS35CA**LAEDDFRQ1.

but there are some question such as:

1. according to TPS35-Q1 spec we choose the MPN TPS35CA**LAEDDFRQ1 as below: see red color

Threshold Voltage is need 2.8v ,this type is it  provided? ,  I can't confirm if 2.8V is available by naming nomenclature show as  below

2.Consider our original design and requirements， the PINOUT C is only options，but has some question as below

2-1:we must add new 3 ports is SET0,SET1,/MR from original(ABLIC S-19400G28A-K8T2U4)  for new design, cause to new Circuit must be redesigned

if SET0,SET1 has no use anymore ,then it will be set to scaling=1 , like bit[0,0] ,  How to deal with these 2 ports？Tie to GND, or  anything to note ?

if  pull it up ,how to do with , such as pull up Resistance Value is ?

2-2:WDI trigger is change to falling edge trigger from  rising edge before ，what does software to  pay attention for?

2-3:the t_SD timming is no need , it is ok?:marked with red line show :

and what dose this t SD time delay function and it is must  necessary?

our original design of ABLIC S-19400G28A-K8T2U4 IC  is no equipped with it 

our original design of  circuits  detail is:

the VDD=3.3V 

MCU:RH850(Renesas)

TWD=11S

TD=65.2ms 

WEN is need

AEC-Q is need

 

thank you and best regards

  • 0
    TI__Genius 9900 points

    Hi Shaofei, 

    Thanks for your question.

    1) Yes, we do have the 2.8V threshold variant. It should be "36" ((36 x 0.05) + 1 = 2.8V). The MPN will be TPS35CA36LAEDDFRQ1

    2.1) Yes, SET0 and SET1 pins can be directly connected to ground to get the watchdog timeout scaling x1.

    Since L=10 sec, when SET0= 0 and SET1 = 0, twd = 10 sec x 1= 10 sec

    If you need your twd =11sec (min), I would recommend connecting SET[1:0] = 0b'10, this way twd = 10sec x 2 =20 sec.

    2.2) A falling transition (edge) must occur at WDI pin before the timeout expires in order for RESET / WDO to not assert. 

    2.3) tsd is the watchdog startup delay and for the MPN that you ae considering  (TPS35xA) there is no tsd delay. 

    And if you don't need MR functionality, the MR pin has 100 kΩ pull up to VDD. The MR pin can be left floating. The internal pull up makes sure the output is not asserted due to MR pin trigger.

    Hope this helps! Please let me know if you have further question!

    Best,

    Sila

  • 0 in reply to Sila Atalar
    Prodigy 10 points

    Dear Sila

    thank you for your support

    I  will share to our relevant engineer for discussion, and request more about it  if there are any problems is need

    best regards

  • 0 in reply to Sila Atalar
    Prodigy 10 points

    HI sila

    thank you for your support

    If we want to use this model,  if  set 10S, we will use the PINOUT C of external capacitor setting , In this case, the model will be TPS35CA36ACADDFRQ1,

    that will 8X scale and cap is setting to 1.25S by these Calculation，tWD result is 10.0188S

    by set[1:0]=0b'10, tell me how resistor of parameter is need to setup? is  also same as /MR with 100Kohm pull up?and  tie it to VDD 3.3V? or go to GND .

    and howmuch is  the pin current value ? because our aplication is in car informatain audio system, VDD 3.3V is from Battery bu +12V->BU 3.3V

    so must pay attention to  the current consumption under the backup conditions

    Here are the options is below: Please confirm again if TPS35CA36ACADDFRQ1 is any problem

    best regards

  • 0 in reply to Sila Atalar
    Prodigy 10 points

    Dear Sila

    can you please reply our new question about TPS35

    best 

  • 0 in reply to shaofei wu
    TI__Genius 11740 points

    Hi Shaofei,

    I will be taking over support for this thread as Sila was covering for me while I was out of office.

    I have a lot of questions regarding this opportunity and use case, therefore I have taken this thread over email.

    Thanks,
    Joshua