ALM2402-Q1: SCG and SCB test

Daniel Wang (auto)

Part Number: ALM2402-Q1
Other Parts Discussed in Thread: ALM2402FQ1EVM

Hello experts,

Hope you are doing well.

Here are some questions when my customer do SCG (short circuit to ground) and SCB (short circuit to battery) test. Kindly invite you to offer some help.

1. SCG

There is an OTF/SH_DN pin in ALM2402-Q1, our customer pull up this pin to 5V through a 10kohm resistor, they did SCG test under different ambient temperature, but found different voltage on the pin:

① When -40℃, the OTF pin 2.52V

② When 25℃, the OTF pin 3.743V

③ When 105 ℃, the OTF pin 3.685V

There are several questions:

what is the recommended pullup resistor of SH_DN pin;
what is the internal structure of this pin, why it is affected by temperature?
It seems that OTF function didn't occur in SCG test under 105C, what's the reason, and then how can MCU find the SCG fault?

2. SCB

When the output short to battery (set 16V by voltage source), the chip was damaged.

Our field team think maybe the supplier voltage rushed to 18V when power on, which is limit of Vcc_(ox), so what is your idea?

And for voltage limit, our customer think 18V is constrained, what is the reason here, and how to improve this situation? (because they think it's usual for the battery voltage exceed the limit)

Thanks very much. Looking forward to your reply.

7 months ago

0 Raymond Zhang1 7 months ago

TI__Guru 50371 points

Hi Daniel,

Daniel Wang (auto) said:
what is the recommended pullup resistor of SH_DN pin;

what is the internal structure of this pin, why it is affected by temperature?

The recommended pull-up resistor is approx. 2.5kΩ at 5Vdc, which is specified in the datasheet. I realized that it is not clearly specified in the datasheet and ALM2402FQ1EVM.

Could you check out the 2.5kΩ pull-up resistor over temperature? Perhaps the pin may be less sensitive to the temperature changes. SH_DN/OTF is considered as digital logic pin, the enable or operating state is above 1V or the pin is in "On" state. So it is not an issue if pin's logic drops slightly, say 2.52V at -40C, which it is above the minimum 1V per the logic definition, see the captured plot above.

The SH_DN/OTF pin's absolute max. rating is specified below 7Vdc. The customer SH_DNOTF's implementation is correct. There is no additional voltage clamp internally at the pin.

Daniel Wang (auto) said:
It seems that OTF function didn't occur in SCG test under 105C, what's the reason, and then how can MCU find the SCG fault?

ALM2402FQ1's thermal shutdown or Tj is high at approx. 165C. If the Tj temperature does not exceed the threshold, the OTF thermal protection pin will not be activated. Typically, the may be the case, if the SCG test is conducted at room temperature.

Daniel Wang (auto) said:
what is the reason here, and how to improve this situation? (because they think it's usual for the battery voltage exceed the limit)

Please verify the battery's voltage when the output pin is shorted to battery. If the battery voltage exceed the abs. max. rating, then the part can be damaged. Enclosed is the overvoltage protection application note on the topic. If you need additional assistant or simulation analysis, please let me know.

https://www.ti.com/lit/an/sboa447/sboa447.pdf?ts=1698679534541&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FALM2403-Q1%253Futm_source%253Dgoogle%2526utm_medium%253Dcpc%2526utm_campaign%253Dasc-amps-null-44700045336317104_prodfolderdynamic-cpc-pf-google-wwe_int%2526utm_content%253Dprodfolddynamic%2526ds_k%253DDYNAMIC%2BSEARCH%2BADS%2526DCM%253Dyes%2526gad_source%253D1%2526gclid%253DCj0KCQjwqP2pBhDMARIsAJQ0Czr9tJ_gJJlMp12PbHjlNm-z4y8UTSwSb7Vn_tqM3EcYUDudU_Hdk80aAg9hEALw_wcB%2526gclsrc%253Daw.ds

Best,

Raymond

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ALM2402-Q1: SCG and SCB test