Sense

resistor

Ground

Shield

Filter Circuit

0.1 µF

0.1 µF

0.1 µF

100

100

0.001, 50 ppm

27

BQ28Z610-R1

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SLUSE07 – JANUARY 2020

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Layout Guidelines (continued)

temperature coefficient no greater than 50 ppm in order 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 BQ28Z610-R1. Select the smallest value possible in order to minimize the negative

voltage generated on the BQ28Z610-R1 VSS node(s) 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.

•

A pair of series 0.1-μF ceramic capacitors is placed across the PACK+ and PACK– pins to help in the

mitigation of external electrostatic discharges. The two devices in series ensure continued operation of the

pack if one of the capacitors becomes shorted. Optionally, a transorb such as the SMBJ2A can be placed

across the pins to further improve ESD immunity.

•

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

•

The BQ28Z610-R1 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. Optional 0.1-μF filter capacitors can be added for additional noise filtering for each

sense input pin to ground, if required for your circuit. 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 add additional noise immunity.

Figure 24. BQ28Z610-R1 Differential Filter

•

The BQ28Z610-R1 has an internal LDO that is internally compensated and does not require an external

decoupling capacitor. The PBI pin is used as a power supply backup input pin, providing power during brief

transient power outages. A standard 2.2-μF ceramic capacitor is connected from the PBI pin to ground, as

shown in application example.

•

internal pull-down. 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.