FDC2112: FDC2112 shut down mode consumption issue

PHILIP HSU

Expert 1900 points

Part Number: FDC2112
Other Parts Discussed in Thread: FDC2114

Hi Sir,.

From the datasheet, the shutdown mode should be 200nA.

In our test on EVM and our PCBA, the FDC power is 1.9mA even we pull the SD pin to high (3.3V).

It seems that the SD pin could not change the power mode from active to shutdown mode.

Do you know the potential problem for this kind of situation?

what`s exception that “⁽⁵⁾ I2C read/write communication and pull-up resistors current through SCL, SDA not included” ,

over 6 years ago

0 Kristin Jones93 over 6 years ago

TI__Genius 17440 points

Hi Philip,

How are you measuring the current draw of the FDC2112?

The quote you mentioned means that the specified typical Idd (2.1mA) does not include the current drawn from I2C communication and the I2C pull-up resistors.

Regards,

0 PHILIP HSU over 6 years ago in reply to Kristin Jones93

Expert 1900 points

Hi KRISTIN,.

Customer use this EVM board for power measurement.

and supply 3.3V and check the current by the power meter.

No matter it tight SD to 3.3V or not, the current on the 3.3V is always 1.9mA.

In our PCBA, it also has the same result.

they like to know where is the problem.

0 Kristin Jones93 over 6 years ago in reply to PHILIP HSU

TI__Genius 17440 points

Hi Philip,

Just to clarify the setup, has your customer broken the MSP430 section of the EVM apart from the FDC2112 section of the EVM? And they are supplying 3.3V to connector J3? Could you also verify that the SD pin is low when it is not tied to 3.3V?

Regards,

0 PHILIP HSU over 6 years ago in reply to Kristin Jones93

Expert 1900 points

Hi Kristin,.

- SD pin not connect (0.5V), 1.93mA at 3.3V

- SD pin connect to 3.3V, 1.85mA at 3.3V

- SD pin connect to ground, 1.93mA at 3.3V

would WE connect application field to customer for DIN risk please ,...

0 Kristin Jones93 over 6 years ago in reply to PHILIP HSU

TI__Genius 17440 points

Hi Philip,

Thank you for the additional information. Could you clarify whether or not the MSP430 is still connected to the FDC2114?

Regards,

0 PHILIP HSU over 6 years ago in reply to Kristin Jones93

Expert 1900 points

Hi Kristin,.

there is no any MCU connection, and FDC2114 AFE measurement only,

please clarify the symptoms, thanks

0 Kristin Jones93 over 6 years ago in reply to PHILIP HSU

TI__Genius 17440 points

Hi Philip,

I have replicated the customer's setup on my bench and have observed the same behavior - the current draw does not change when SD is pulled high. I will investigate to see if this is an issue with the EVM. I'll update this thread as soon as I have more information to share.

Regards,

0 PHILIP HSU over 6 years ago in reply to Kristin Jones93

Expert 1900 points

KRISTIN,.

please have a conclusion as soon as possible,.

it cause of design risk and pended customer project few times, it`s concern and affect the AFE product ,...

please help

0 Kristin Jones93 over 6 years ago in reply to PHILIP HSU

TI__Genius 17440 points

Hi Philip,

I have investigated this issue and have some preliminary suggestions for you. If other pins (SDA, SCL, ADDR, and CLKIN) are not tied to either ground or VDD during shutdown mode, this can increase current draw. I suggest testing the current draw with these pins shorted to GND or SD. Please let me know if you see an improvement in the current draw with these modifications to your customer's test setup.

Regards,

0 PHILIP HSU over 6 years ago in reply to Kristin Jones93

Expert 1900 points

Hi KRISTIN,.

It could help a little bit on the leakage current.
Original current is around 1.88mA, and it is 1.79mA if we tie I2C/ADDR/SD to 3.3V.
customer think we did not solve the shut down current issue yet.

please have root cause suggestion in further,...it was pended and bad situation

0 PHILIP HSU over 6 years ago in reply to PHILIP HSU

Expert 1900 points

Hi KRISTIN,.
I had added you in friend loop, please help

0 Kristin Jones93 over 6 years ago in reply to PHILIP HSU

TI__Genius 17440 points

Hi Philip,

I have reproduced the normal shutdown current draw in the lab. I am measuring less than 1uA when the shutdown pin is pulled high. To achieve this current, it is absolutely critical to gate the reference clock. I mimicked this on the EVM by desoldering the external oscillator, soldering a wire to R22, and shorting this wire to the shutdown pin. This made a huge difference in the current draw. I think this is the key difference between our two setups. I saw that you pulled the I2C lines, ADDR, and SD to 3.3V, but you did not mention CLKIN.

I also disconnected the I2C communication between the MCU and the FDC2114. This further reduced the current draw.

For more information about low power capacitive sensing, including clock gating, please see this application note.

Regards,

0 PHILIP HSU over 6 years ago in reply to Kristin Jones93

Expert 1900 points

YES KRISTIN,.
thanks , it`s great to the conclusion, thanks for the solution,.

Regards,
Philip

Because of the Thanksgiving holiday in the U.S., TI E2E™ design support forum responses may be delayed from November 25 through December 2. Thank you for your patience.

Data converters

Data converters forum

FDC2112: FDC2112 shut down mode consumption issue