9.3 Power Supply Recommendations

The only power supply is the BAT pin, which is connected to the positive terminal of the battery. The input

voltage for the BAT pin will have a minimum of 2 V to a maximum of 5 V.

9.4 Layout

9.4.1 Layout Guidelines

• The quality of the Kelvin connections at the sense resistor is critical. The sense resistor must have a

temperature coefficient no greater than 50 ppm to minimize current measurement drift with temperature.

Choose the value of the sense resistor to correspond to the available overcurrent and short-circuit ranges of

the BQ27Z561-R2 gas gauge. Select the smallest value possible to minimize the negative voltage generated

on the BQ27Z561-R2 VSS node during a short circuit. This pin has an absolute minimum of –0.3 V. Parallel

resistors can be used as long as good Kelvin sensing is ensured. The device is designed to support a 1-mΩ

to 3-mΩ sense resistor.

• BAT_SNS should be tied directly to the positive connection of the battery. It should not share a path with the

BAT pin.

• In reference to the gas gauge circuit the following features require attention for component placement and

layout: differential low-pass filter and I2C communication.

• The BQ27Z561-R2 gas gauge uses an integrating delta-sigma ADC for current measurements. Add a 100-Ω

resistor from the sense resistor to the SRP and SRN inputs of the device. Place a 0.1-μF filter capacitor

across the SRP and SRN inputs. If required for a circuit, 0.1-µF filter capacitors can be added for additional

noise filtering for each sense input pin to ground. Place all filter components as close as possible to the

device. Route the traces from the sense resistor in parallel to the filter circuit. Adding a ground plane around

the filter network can provide additional noise immunity.

• The BQ27Z561-R2 has an internal LDO that is internally compensated and does not require an external

decoupling capacitor.

• The I2C clock and data pins have integrated high-voltage ESD protection circuits; however, adding a Zener

diode and series resistor provides more robust ESD performance. The I2C clock and data lines have an

internal pulldown. When the gas gauge senses that both lines are low (such as during removal of the pack),

the device performs auto-offset calibration and then goes into SLEEP mode to conserve power.

BQ27Z561-R2

SLUSE22B – FEBRUARY 2020 – REVISED NOVEMBER 2022

www.ti.com

18

Submit Document Feedback

Copyright © 2022 Texas Instruments Incorporated

Product Folder Links: BQ27Z561-R2