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SHUNT SHUNT

SHUNT

V V

R 1000

§ ·

¨ ¸

ADC

VDDSHUNT ADC

VDDSHUNT

V V

100

R 0.1 10

u u

ADC VDDSHUNT VDDSHUNT

V V Gain V 100

VDDSHUNT VDDSHUNT

VDDSHUNT

V V

R 0.1

Hibernate, Current Shunts, Power Supplies, Reset and Crystals (Schematic page 3)

www.ti.com

The DK-TM4C123G has additional circuitry that allows the development board to be turned on when a

battery is not present or when the battery voltage is too low. A Texas Instruments TPS3803-01 Voltage

Detector (U12) monitors V

BAT

and produces a VBAT_GOOD signal when the battery voltage is above 2.1

V. Using standard logic gates and the state of V

BAT

and V

, the HIB signal can be forced high when V

BAT

is not valid and the microcontroller is not already powered. With this circuit, a USB-powered board can

turn itself on when the back-up battery is either missing or fully discharged. See Appendix A: Schematics

for more details.

This additional circuitry may not be needed in all applications. For example, when using the Hibernate

module in VDD3ON mode, power is cut to the microcontroller internally which eliminates the need to turn

off an external supply using HIB. By default the DK-TM4C123G is not configured to use VDD3ON mode;

HIB is connected to the load switch, WAKE is pulled up to V

BAT

, and V

BAT

is connected to the battery.

VDD3ON mode can be used if the board is reconfigured as follows

(2)

: Disconnect HIB from the load swich

by removing the HIB DISC jumper (JP3). Next, ensure that WAKE is pulled HIGH either by leaving the

battery connected or by removing the battery and connecting V

BAT

to V

CAUTION

Failure to remove the battery when connecting V

BAT

to V

will damage the

battery and can cause a fire.

There are many different ways that Hibernate mode can be implemented in an embedded system. Each

implementation requires its own special design considerations.

2.3.2 Current Shunt Resistors

The development board provides two current shunt resistors to measure the MCU running current, I

, and

the hibernation battery current, I

VBAT

. I

can be measured by the MCU through a TI INA198 Current Shunt

Amplifier (U15). See MCU Running Current section. I

BAT

must be measured externally.

2.3.2.1 Microcontroller Running Current I

VDD

The shunt resistor for I

, R

VDDSHUNT

, is 0.1Ω and the INA198 amplifier gain is 100 V/V. Therefore:

(8)

(9)

Given the ADC measurement, you can calculate I

VDD

(10)

Or simply, 10mV per mA.

2.3.2.2 Hibernation Battery Current I

BAT

The shunt resistor for I

VBAT

, R

VBATSHUNT

, is 1kΩ.

(11)

Or simply 1 mV per µA.

(2)

In addition to reconfiguring the hardware, the software must also be reconfigured to use VDD3ON mode.

Hardware Description SPMU357B–August 2013–Revised March 2014

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