MSP430FR5969: LPM4 power consumption is high depending on ADC input

Koichiro Tashiro

Hi,

My customer reported below issue with MSP430FR5969.
In their system, battery voltage(Vbat) is monitored by MSP430 ADC (P4.2/A10 is used as input).
The customer found LPM4 current consumption is too high depending on Vbat voltage and how it is connected to A10 input.

When Vbat is 3.0V;
- Connecting Vbat to A10 via 1M ohm resistor shows expected current (a few uA).
- Connecting Vbat to A10 via voltage divider (1M Ohm / 1M Ohm) shows 100uA to 250uA.

When Vbat is 1.5V;
- Connecting Vbat to A10 via 1M ohm resistor shows 100uA to 250uA.
- Connecting Vbat to A10 via voltage divider (1M Ohm / 1M Ohm) shows expected current (a few uA).

Please see below figures.

The current is measured at power IC(TPS610993) input.
Vbat is supplied to TPS610993 and Vd=3.0V is supplied to MSP430.

Why such behavior is observed and how to solve it?

Thanks and regards,
Koichiro Tashiro

over 5 years ago

0 Eason Zhou over 5 years ago

TI__Mastermind 40195 points

See from the result, it shows that when the A10 input voltage is 3V or 0.75V, it works good. When A10 input voltage is 1.5V, it doesn't works good.

It is quite strange, I can't come up any idea that why it happens.

1. Can customer try to decrease the resistor to kR level to see if it helps.

2. Change the input voltage from 3V to 0.75V with a small step to check whether you can see the same result at different voltage.

0 Koichiro Tashiro over 5 years ago in reply to Eason Zhou

TI__Mastermind 22945 points

Hi Eason,

Thanks for your quick reply.

Eason Zhou said:
1. Can customer try to decrease the resistor to kR level to see if it helps.

2. Change the input voltage from 3V to 0.75V with a small step to check whether you can see the same result at different voltage.

Due to hardware constrains, customer cannot try them.

According to datasheet Table 5-11, High-impedance input leakage current is +/-20nA.
Suppose the power supply is 3.0V, input impedance is 3V/20nA = 150MOhm.
So an external resistor ~1MOhm should not be add any impact, correct?

BTW, customer found below description in User’s Guide.
If ADC is enabled unexpectedly under LPM4, does this relate to this issue?

Thanks and regards,
Koichiro Tashiro

0 Eason Zhou over 5 years ago in reply to Koichiro Tashiro

TI__Mastermind 40195 points

I think yes. ADC maybe unexpected working at LPM4. Please refer to the chart bellow:

+1 Bruce McKenney over 5 years ago in reply to Koichiro Tashiro

Guru 102955 points

Based (solely) on the voltage levels you mention, my first guess is that the Schmitt triggers are still enabled, i.e. the PSEL bits aren't set appropriately (0b11). [Ref UG (SLAU367P) Sec 34.2.2.1]

0 Koichiro Tashiro over 5 years ago in reply to Bruce McKenney

TI__Mastermind 22945 points

Hi Bruce,

Thanks for your comment.
In fact customer configures PSEL bits to 00b (P4.2 input HiZ) before LPM4 entry.
Customer will change it to 11b and check power consumption on Jul.15 (due to COVID19, lab work is limited).
I will let you know the result soon.

Thanks and regards,
Koichiro Tashiro

0 Eason Zhou over 5 years ago in reply to Koichiro Tashiro

TI__Mastermind 40195 points

Hi Bruce,

Thank you for your catch. Really learn a lot.

Eason

0 Koichiro Tashiro over 5 years ago in reply to Eason Zhou

TI__Mastermind 22945 points

Customer confirmed the issue was resolved with PSEL=11b.
Thanks a lot for your help!

Thanks and regards,
Koichiro Tashiro

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MSP430FR5969: LPM4 power consumption is high depending on ADC input