Charge and Discharge Counting

Voltage

Current

Wake Function

Auto Calibration

Temperature

COMMUNICATIONS

SMBus On and Off State

bq20z40

The integrating delta-sigma ADC measures the charge/discharge flow of the battery by measuring the voltage

drop across a small-value sense resistor between the SRP and SRN pins. The integrating ADC measures bipolar

time, using an internal counter. The fundamental rate of the counter is 0.65 nVh.

The bq20z40 updates the individual series cell voltages through the bq29330 at one second intervals. The

bq20z40 configures the bq29330 to connect the selected cell, cell offset, or bq29330 VREF to the CELL pin of

the bq29330, which is required to be connected to VIN of the bq20z40. The internal ADC of the bq20z40

measures the voltage, scales it, and calibrates itself appropriately. This data is also used to calculate the

impedance of the cell for the Impedance Track™ gas-gauging.

The bq20z40 uses the SRP and SRN inputs to measure and calculate the battery charge and discharge current

using a 5 m

Ω to 20 mΩ typ. sense resistor.

The bq20z40 can exit sleep mode, if enabled, by the presence of a programmable level of current signal across

SRP and SRN.

The bq20z40 provides an auto-calibration feature to cancel the voltage offset error across SRP and SRN for

maximum charge measurement accuracy. The bq20z40 performs auto-calibration when the SMBus lines stay

low continuously for a minimum of a programmable amount of time.

The bq20z40 has an internal temperature sensor and inputs for 2 external temperature sensors, TS1 and TS2,

used in conjunction with two identical NTC thermistors (default are Semitec 103AT) to sense the battery

environmental temperature. The bq20z40 can be configured to use internal, or up to 2 external temperature

sensors.

The bq20z40 uses SMBus v1.1 with Master Mode and package error checking (PEC) options per the SBS

specification.

The bq20z40 detects an SMBus off state when SMBC and SMBD are logic-low for

≥ 2 seconds. Clearing this

state requires either SMBC or SMBD to transition high. Within 1 ms, the communication bus is available.

10

Submit Documentation Feedback

Copyright © 2009, Texas Instruments Incorporated

Product Folder Link(s) :bq20z40