BQ25120_15 Datasheet, PDF (19/68 Pages) Texas Instruments – bq25120 700-nA Low IQ Highly Integrated Battery Charge Management Solution for Wearables and IoT

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BQ25120
SLUSBZ9A – AUGUST 2015 – REVISED AUGUST 2015
9.3.4 Voltage Based Battery Monitor
The device implements a simple voltage battery monitor which can be used to determine the depth of discharge.
Prior to entering High-Z mode, the device will initiate a VBMON reading. The host can read the latched value for
the no-load battery voltage, or initiate a reading using VBMON_READ to see the battery voltage under a known
load. The register will be updated and can be read 2ms after a read is initiated. The VBMON voltage threshold is
readable with 2% increments with ±1.5% accuracy between 60% and 100% of VBATREG using the VBMON_TH
registers. Reading the value during charge is possible, but for the most accurate battery voltage indication, it is
recommended to disable charge, initiate a read, and then re-enable charge.
A typical discharge profile for a Li-Ion battery is shown in Table 2. The specific battery to be used in the
application should be fully characterized to determine the thresholds that will indicate the appropriate battery
status to the user. Two typical examples are shown below, assuming the VBMON reading is taken with no load
on the battery.
This function enables a simple 5-bar status indicator with the following typical performance with different
VBATREG settings:
VBATREG
4.35 V
4.2 V
Table 2. Discharge Profile for a Li-Ion Battery
BATTERY FULL
VBMON > 90%
VBMON > 98%
95% to 65%
65% to 35%
35% to 5%
REMAINING CAPACITY REMAINING CAPACITY REMAINING CAPACITY
VBMON = 88%
VBMON = 86%
VBMON = 84%
VBMON = 94% or 96% VBMON = 90% or 92% VBMON = 86% or 88%
BATTERY EMPTY
VBMON < 82%
VBMON < 84%
VREF
90 % VB
S0
-2 % BAT TAP
-4 % BAT TAP
-6 % BAT TAP
-8 % BAT TAP
-10 % BAT TAP
S1
D
E
80 % VB
S2
C
O
D
E
R
70 % VB
S3
60 % VB
VB = 0. 8 VBAT
Figure 14. Voltage Battery Monitor
Copyright © 2015, Texas Instruments Incorporated
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