BQ25700A Datasheet, PDF (52/82 Pages) Texas Instruments – SMBus Multi-Chemistry Battery Buck-Boost Charge Controller With System Power Monitor and Processor Hot Monitor

bq25700A
SLUSCQ8 – MAY 2017
www.ti.com
8.6.5 MinSystemVoltage Register (SMBus address = 3Eh) [reset value based on CELL_BATPRESZ pin
setting]
To set the minimum system voltage, write a 16-bit MinSystemVoltage register command (REG0x3E()) using the
data format listed in Table 29 and Table 30. The charger provides minimum system voltage range from 1.024 V
to 16.128 V, with 256-mV step resolution. Any write below 1.024 V or above 16.128 V is ignored. Upon POR, the
MinSystemVoltage register is 3.584 V for 1 S, 6.144 V for 2 S and 9.216 V for 3 S, and 12.288 V for 4 S.
Figure 28. MinSystemVoltage Register (SMBus address = 3Eh) [reset value based on CELL_BATPRESZ
pin setting]
15
14
Reserved
R/W
13
Min System
Voltage, bit 5
R/W
12
Min System
Voltage, bit 4
R/W
11
Min System
Voltage, bit 3
R/W
10
Min System
Voltage, bit 2
R/W
9
Min System
Voltage, bit 1
R/W
8
Min System
Voltage, bit 0
R/W
7
6
5
4
3
2
1
0
Reserved
R/W
LEGEND: R/W = Read/Write; R = Read only; -n = value after reset
Table 29. MinSystemVoltage Register (SMBus address = 3Eh) Field Descriptions
SMBus
BIT
15-14
13
12
11
10
9
8
FIELD
TYPE
RESET DESCRIPTION
Reserved
R/W
00b
Not used. 1 = invalid write.
Min System Voltage, bit 5
R/W
0b
0 = Adds 0 mV of system voltage.
1 = Adds 8192 mV of system voltage.
Min System Voltage, bit 4
R/W
0b
0 = Adds 0 mV of system voltage.
1 = Adds 4096mV of system voltage.
Min System Voltage, bit 3
R/W
0b
0 = Adds 0 mV of system voltage.
1 = Adds 2048 mV of system voltage.
Min System Voltage, bit 2
R/W
0b
0 = Adds 0 mV of system voltage.
1 = Adds 1024 mV of system voltage.
Min System Voltage, bit 1
R/W
0b
0 = Adds 0 mV of system voltage.
1 = Adds 512 mV of system voltage.
Min System Voltage, bit 0
R/W
0b
0 = Adds 0 mV of system voltage.
1 = Adds 256 mV of system voltage.
Table 30. MinSystemVoltage Register (SMBus address = 3Eh) Field Descriptions
SMBus
BIT
7-0
FIELD
Reserved
TYPE
R/W
RESET DESCRIPTION
0000000 _{Not used. Value Ignored.}
0b
8.6.5.1 System Voltage Regulation
The device employs Narrow VDC architecture (NVDC) with BATFET separating system from battery. The
minimum system voltage is set by REG0x3E(). Even with a deeply depleted battery, the system is regulated
above the minimum system voltage with BATFET.
When the battery is below minimum system voltage setting, the BATFET operates in linear mode (LDO mode),
and the system is regulated above the minimum system voltage setting. As the battery voltage rises above the
minimum system voltage, BATFET is fully on when charging or in supplement mode and the voltage difference
between the system and battery is the VDS of BATFET. System voltage is regulated 160 mV above battery
voltage when BATFET is off (no charging or no supplement current).
When BATFET is removed, the system node VSYS is shorted to SRP. Before the converter starts operation,
LDO mode needs to be disabled. The following sequence is required to configure charger without BATFET.
1. Before adapter plugs in, put the charger into HIZ mode. (either pull pin 6 ILIM_HIZ to ground, or set
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