BQ28550-R1 Datasheet, PDF (15/42 Pages) Texas Instruments – Single Cell Li-Ion Battery Gas Gauge

Not Recommended for New Designs
www.ti.com
bq28550-R1
SLUSAS4A – OCTOBER 2012 – REVISED SEPTEMBER 2014
Protection (continued)
7.5.4 Charge Overcurrent Detector
If the voltage across both protection MOSFETs (V_M – V_SS) becomes more negative than the charge overcurrent
detection voltage (V_DET4 = –0.112 V typ) for a period up to the charge overcurrent detection delay time
(t_DET4 = 12 ms typ) due to an abnormal charging current or abnormal charging voltage, the bq28550-R1 device
detects the overcurrent charge state of the battery and the COUT pin transitions to a low level. This prohibits
charging the battery by turning off the external charge control N-channel MOSFET. The bq28550-R1 device
releases from the charge overcurrent detection state on by detecting the connection of a load for a period up to
the overcharge release delay time (t_REL4 = 4 ms typ).
Table 1. Hardware Control Due to Fault Detection
Fault Condition
Overcharge Voltage
Protection
Overcurrent
Protection During
Charging
Over Discharging
Voltage Protection
Overcurrent
Protection During
Discharging
Short-Circuit
Protection
DOUT
ON
ON
OFF
OFF
OFF
COUT
OFF
OFF
ON
ON
ON
Delay
(typ)
1s
12 ms
24 ms
12 ms
400 µs
Comment
Once OVP occurs for longer than the specified duration (1 s typ), the CHG FET is turned
OFF and bus communication is NOT valid. The system will support power to the load with
current flow through the CHG FET parasitic diode. This can cause the cell to discharge;
once the cell voltage reaches the overcharge release voltage for the specified duration (8
ms typ), the CHG FET is turned ON and bus communication is valid.
If the cell is being charged with excessive current, the threshold will be based on a
hardware limit measurement of –112 mV typ across the CHG + DSG FET (VM – Vss) for
a duration longer than 12 ms (typ), the CHG FET is turned OFF and bus communication
is not valid. This will prevent further charging of the cell. The setting of the CHG bit in the
control Status Register is dependent on the OC bit setting in the Charge Fault Register
selection. The FET bit in the Control between the charger is removed and cell voltage
falls below the threshold for greater than 8 ms (typ). COUT is turned back ON. Once the
host MCU takes corrective action OR if the battery charger is removed AND there is a
load detected for a period of 4 ms (typ), the CHG FET is turned ON and bus
communication is valid.
If the cell voltage falls to lower than 2.3 V for a duration of 24 ms (typ), the DSG FET is
turned OFF, and bus communication is not valid. The system requires if the charger is
connected and cell voltage rises above threshold for greater than 4 ms (typ), DOUT is
turned back ON and bus communication is valid.
If the cell is being discharged with excessive current, the threshold will be based on a
hardware limit measurement of 150 mV typ across the DSG + CHG FET (VM – Vss) for a
duration longer than 12 ms (typ) the DSG FET is turned OFF and bus communication is
NOT valid. This will prevent further discharging of the cell, and the DSG bit in the control
Status Register will be set. If the drop across the DSG + CHG FET is less than the
threshold OR there is no load detected for a duration of 4 ms (typ), the DSG FET is
turned ON and bus communication is valid.
Detection of cell short circuit is measured at VM input. Shorted cell detection is V_BAT –
0.9 V for greater than 400 µs at the VM terminal, and the DSG FET is turned OFF, and
bus communication is NOT valid. The DSG bit in the control Status Register will be set.
The system will turn the DSG FET ON if the voltage at VM is below 150 mV OR no load
is detected.
7.5.5 Gas Gauge Control of Discharge DOUT Pin
Firmware Control of DOUT for Protection
The gas gauge firmware can override the hardware-based protection by forcing DOUT low to turn OFF the
discharge FET. However, the firmware cannot override the hardware protection to force discharge.
There are three conditions that enable firmware to force DOUT low:
1. The HOST_DISCONNECT (DSG FET OFF) subcommand: This feature is useful for the system to disable
the discharge FET from the battery pack if it fails to authenticate.
2. Pack removal detection by the SDA and SCL pins falling low for more than 2 seconds: The DOUT pin
override condition is released upon detection of PACK insertion.
3. Firmware-based undervoltage detection: The DOUT pin is forced low if voltage of the cell falls below the Set
Voltage threshold. The DOUT override condition is released when the voltage is above Clear Voltage.
Any one of the above three conditions will force the DOUT pin low. However, all three corresponding release
conditions must be satisfied before the DOUT override is returned to hardware-based protection control.
Copyright © 2012–2014, Texas Instruments Incorporated
Product Folder Links: bq28550-R1
Submit Documentation Feedback
15