TM4C1231E6PM. query

Hello Utpal,

1. I'm a bit confused as to what IIH and IIL is. I am guessing you are asking what the leakage current is when the pin is set to an input and is driven high or low.  According to the GPIO module Characteristics table found in the Input/Output pin Characteristics section of the data sheet. the leakage current is 1.0 uA if the Voltage is between 0 and Vdd when set as GPIO and the leakage current is 2uA when set as ADC or Analog comparator pins. This will increase if you are using an internal pull up or pull down.  Please let me know if this is not what you were asking. 

2. There is no battery reversal protection built into the VBAT pin, I do not have any suggestions of the top of my head.

3. This is correct, it will use what ever voltage is higher to power the hibernation module on the. TM4C1231E6PM.

Sheldon

Hello Sheldone,

Thanks for your earlier reply regarding the Battery. In our case we are using a separate battery for supplying VBAT pin with the suggested circuit. It will be used for only RTC operation. In normal operation, TM4C1231E6PM will be supplied with external 3.3V. When there is power failure, this 3.3V will be switched OFF, so there will be only battery connected to VBAT pin as shown below.

Please confirm this scinario works fine for RTC operation, as we are not using any switching circuit from normal 3.3V supply to battery?

Also please let us know whether there will be any considerable load on the battery because of the RBAT and CBAT network and RPU resistor shown. If there is considerable load, we will connect battery directly to VBAT pin.

One more clarification is regarding WAKE# Pin. Do we need to really pull up to battery supply voltage while using RTC mode only in hibernation module? or can we leave this pin open or grounded? as we don't have any wake up events in our application. Only RTC will be running all the time whether VCC=3.3V supply is ON or switched OFF.

Please clarify on the above.

Thanks,

Dhoresh

Dhoresh,

Please see the errata document.

http://www.ti.com/lit/pdf/spmz849

ELEC#02 VBAT Supply pin may be Damaged if the pin Voltage Ramps Faster Than 0.7 V/μs X X

The load on VBAT will not be major as long as the 3.3V Source is available. In case of the 3.3V source failing the VBAT current is mentioned in the Current Consumption Section of the Electrical Specifications. It is advisable not to leave WAKE_N Pin Floating. Instead a Rpu=1M would be good

Amit

Hello Amit,

Thanks for the reply.

That means, I can proceed with the circuit shown in my earlier query ?

Thanks,

Dhoresh

Hello Dhoresh

Yes, you can proceed with the circuit.

Amit

Referencing the VBAT R-C Circuit where a 51 Ohm and 0.1uF are recommended to control the VBAT ramp-rate.

I would like to increase the 51 Ohm resistor to 390 Ohms.

This is because the testing agencies are focusing on the case of a failure internal to the microcontroller causing the 3.3VDC VCC voltage sourcing current to the external battery. 

Since the battery we are using has a maximum specified charge current of 10 mA.

3.3 V / 51 Ohms = 65 mAmp worse case charging current (assuming a dead battery and a short inside the microcontroller).

3.3 V / 390 Ohms = 8.5 mAmp worse-case chargin current (assuming a dead battery and a short inside the microcontroller). 

is there any reason I should not increase this VBAT resistance from 51 Ohms to 390 Ohms?

Could this increase from 51 Ohms to 390 Ohms cause any problems with the operation of the RTC in the Hibernation module? 

Thank you,

Mike