LM74610-Q1: T0/T1 time

LIN SUN

Part Number: LM74610-Q1

Dear expert:

I’m using 4.7uF Vcap according to reference design.

When my probe is placed at net VBAT_F, T0/T1 are 33ms/2464ms, respectively. However, according to formula1 of spec page10, T0/T1 should be 100ms/5.7s, respectively. Why my result is so different from spec calculated?

BTW, When my probe is placed at net VBAT_F, and another probe is also placed at LM74610 pin 7 (VCAPH), T0/T1 are 33ms/830ms, respectively. It seems that VCAP discharge time is largely reduced due to probe. Can you share me some precious suggestions please?

over 5 years ago

0 Karikalan Selvaraj over 5 years ago

TI__Genius 16305 points

Probing VCAPH (Pin 7) with reference to GND will add leakage path for charge pump and would discharge VCAPH. This would reduce turn on time.

However if VBAT_F is probed it should not reduce the turn on time so much.

We will review and get back to you later this week, but is this happening on one IC or more than one IC?

Regards,

Kari.

0 LIN SUN over 5 years ago in reply to Karikalan Selvaraj

Intellectual 620 points

Dear expert Kari

Two boards and three LM74610 are tested. Same results are found. Hoping for your reply and thanks!

0 Karikalan Selvaraj over 5 years ago in reply to LIN SUN

TI__Genius 16305 points

Hi LIN SUN,

We are investigating the variation observed on VBAT_F ON time and would require some time until early next week to get back on this.

In the meantime, if can share the variation in 4.7uF capacitance, that will help to debug faster.

Regards,

Kari.

0 LIN SUN over 5 years ago in reply to Karikalan Selvaraj

Intellectual 620 points

Hi kari

4.7uF_±10%_25V_X5R_0603 is used, supplier P/N is CL10A475KA8NQNC and specification attached.CL10A475KA8NQNC.pdf

0 Karikalan Selvaraj over 5 years ago in reply to LIN SUN

TI__Genius 16305 points

HI Lin,

We have looked at this isssue in detail now.

One reason where this can happen is due to increase in leakage current across VCAPH and VCAPL pins.

Can you please remove the IC and measure the leakage across the 4.7uF capacitor (VCAPH to VCAPL) by connecting a 1V source and measuring the current through.

Any leakage current of about 200nA to 300nA can cause this issue.

Regards,

Kari.

0 LIN SUN over 5 years ago in reply to Karikalan Selvaraj

Intellectual 620 points

HI KARI

Leakage current cannot be measured, because my power supply has no such high precision. Can you share your experience with me please? I cannot understand it well. Thanks!

0 Karikalan Selvaraj over 5 years ago in reply to LIN SUN

TI__Genius 16305 points

Can you use a power supply and ammeter(digital multimeter) in series to measure?

Regards,

Kari.

0 Karikalan Selvaraj over 5 years ago in reply to Karikalan Selvaraj

TI__Genius 16305 points

Leakage needs to be measured on the board:

1. Remove the LM74610-Q1 IC from the board .

2. Connect power supply between 4.7uF capacitor and with ammeter (multimeter) in series to the power supply line. Ammeter or multimeter need to be set to low current range or auto range.

3. Set power supply to 5V and measure the leakage current

Could you help us with this measurement data?.

Regards,

Kari.

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LM74610-Q1: T0/T1 time