9.2.1 Design Requirements

Table 9-1 shows the default settings for the main parameters. Use the BQSTUDIO tool to update the settings to

meet the specific application or battery pack configuration requirements.

The device should be calibrated before any gauging test. Follow the procedures on the BQSTUDIO Calibration

page to calibrate the device, and use the information on the BQSTUDIO Chemistry page to update the match

chemistry profile to the device.

Table 9-1. Design Parameters

DESIGN PARAMETER

EXAMPLE

Cell Configuration

3s1p (3-series with 1 parallel)(1)

Design Capacity

4400 mAh

Device Chemistry

1210 (LiCoO2/graphitized carbon)

Cell Overvoltage at Standard Temperature

4300 mV

Cell Undervoltage

2500 mV

Shutdown Voltage

2300 mV

Overcurrent in CHARGE Mode

6000 mA

Overcurrent in DISCHARGE Mode

–6000 mA

Short Circuit in CHARGE Mode

0.1 V/Rsense across SRP, SRN

Short Circuit in DISCHARGE Mode

0.1 V/Rsense across SRP, SRN

Safety Overvoltage

4500 mV

Cell Balancing

Disabled

Internal and External Temperature Sensor

External temperature sensor is used.

Undertemperature Charging

0°C

Undertemperature Discharging

0°C

BROADCAST Mode

Disabled

Battery Trip Point (BTP) with active high interrupt

Disabled

(1)

When using the device the first time and if a 1-s or 2-s battery pack is used, then a charger or power supply should be connected

to the PACK+ terminal to prevent device shutdown. Then update the cell configuration (see the BQ40Z50-R2 Technical Reference

Manual [SLUUBK0] for details) before removing the charger connection.

9.2.2 Detailed Design Procedure

9.2.2.1 High-Current Path

The high-current path begins at the PACK+ terminal of the battery pack. As charge current travels through the

pack, it finds its way through protection FETs, a chemical fuse, the Li-ion cells and cell connections, and the

sense resistor, and then returns to the PACK– terminal (see Figure 9-2). In addition, some components are

placed across the PACK+ and PACK– terminals to reduce effects from electrostatic discharge.

9.2.2.1.1 Protection FETs

Select the N-channel charge and discharge FETs for a given application. Most portable battery applications are a

good match for the CSD17308Q3. The TI CSD17308Q3 is a 47A, 30-V device with Rds(on) of 8.2 mΩ when the

gate drive voltage is 8 V.

If a precharge FET is used, R1 is calculated to limit the precharge current to the desired rate. Be sure to account

for the power dissipation of the series resistor. The precharge current is limited to (VCHARGER – VBAT)/R1 and

maximum power dissipation is (Vcharger – Vbat)2/R1.

The gates of all protection FETs are pulled to the source with a high-value resistor between the gate and source

to ensure they are turned off if the gate drive is open.

Capacitors C1 and C2 help protect the FETs during an ESD event. Using two devices ensures normal operation

if one becomes shorted. To have good ESD protection, the copper trace inductance of the capacitor leads

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BQ40Z50-R2

SLUSCS4C – JUNE 2017 – REVISED APRIL 2021

Copyright © 2021 Texas Instruments Incorporated

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