BQ25120A Datasheet, PDF (20/67 Pages) Texas Instruments – Low IQ Highly Integrated Battery Charge Management Solution for Wearables and IoT

bq25120A
SLUSD08 – MAY 2017
www.ti.com
9.3.3 Active Battery Only Connected
When the battery above V_BATUVLO is connected with no input source, the battery discharge FET is turned on.
After the battery rises above V_BATUVLO and the deglitch time is reached, the SYS output starts to rise. The current
from PMID and SYS is not regulated, but is protected by a short circuit current limit. If the short circuit limit is
reached for the deglitch time (t_{DGL_SC}), the battery discharge FET is turned off for the recovery time (t_{REC_SC}).
After the recovery time, the battery FET is turned on to test if the short has been removed. If it has not, the FET
turns off and the process repeats until the short is removed. This process protects the internal FET from over
current. During this event PMID will likely droop and cause SYS to go out of regulation.
To provide designers the most flexibility in optimizing their system, an adjustable BATUVLO is provided. When
the voltage drops below the V_BATUVLO threshold, the battery discharge FET is turned off. Deeper discharge of the
battery enables longer times between charging, but may shorten the battery life. The BATUVLO is adjustable
with a fixed 150-mV hysteresis.
If a valid V_IN is connected during active battery mode, V_IN > V_UVLO, the supplement and battery discharge FET is
turned on when the battery voltage is above the minimum V_BATUVLO.
Drive CD high or write the CE register to disable charge when V_IN > V_UVLO is present. CD is internally pulled
down. When exiting this mode, charging resumes if V_IN is present, CD is low and charging is enabled.
All HOST interfaces (CD, SDA/SCL, INT, RESET and LSCTRL) are active no later than 5 ms after SYS reaches
the programmed level.
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%
20
Submit Documentation Feedback
Product Folder Links: bq25120A
Copyright © 2017, Texas Instruments Incorporated