BQ24157 Datasheet, PDF (28/39 Pages) Texas Instruments – Fully Integrated Switch-Mode Charger With USB Compliance and USB-OTG Support

bq24157
SLUSB80 – SEPTEMBER 2012
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• Special charger voltage offset is 4.2V and default special charger voltage is 4.52V.
• Default charge current will be 550mA, if 68-mΩ sensing resistor is used, since default LOW_CHG=0.
Table 9. Safety Limit Register (READ/WRITE, Write only once after reset!)
Memory location: 06, Reset state: 01000000
BIT
B7 (MSB)
B6
B5
B4
B3
B2
B1
B0 (LSB)
NAME
V_MCHRG3 ⁽¹⁾
V_MCHRG2 ⁽¹⁾
V_MCHRG1 ⁽¹⁾
V_MCHRG0 ⁽¹⁾
V_MREG3
V_MREG2
V_MREG1
V_MREG0
READ/WRITE
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
Read/Write
FUNCTION
Maximum charge current sense voltage: 54.4 mV step (default 0) ⁽²⁾
Maximum charge current sense voltage: 27.2 mV step (default 1)
Maximum charge current sense voltage: 13.6 mV step (default 0)
Maximum charge current sense voltage: 6.8 mV step (default 0)
Maximum battery regulation voltage: 160 mV step (default 0)
Maximum battery regulation voltage: 80 mV step (default 0)
Maximum battery regulation voltage: 40 mV step (default 0)
Maximum battery regulation voltage: 20 mV step (default 0)
(1) Refer to Table 11
• Maximum charge current sense voltage offset is 37.4 mV (550mA), default at 64.6mV (950mA) and the
maximum charge current option is 1.55A (105.4mV), if 68-mΩ sensing resistor is used.
• Maximum battery regulation voltage offset is 4.2V (default at 4.2V) and maximum battery regulation voltage
option is 4.44V.
• Memory location 06H resets only when V_(CSOUT) drops below V_(SHORT) threshold (typ. 2.05V). After reset, the
maximum values for battery regulation voltage and charge current can be programmed until any writing to
other register locks the safety limits. Programmed values exclude higher values from memory locations 02
(battery regulation voltage), and from memory location 04 (Fast charge current).
• If host accesses (write command) to some other register before Safety limit register, the safety default values
are used.
APPLICATION SECTION
Charge Current Sensing Resistor Selection Guidelines
Both the termination current range and charge current range depend on the sensing resistor (R_SNS). The
termination current step (I_{OTERM_STEP}) can be calculated using Equation 1:
I_{O(TERM_STEP)}
=
V_I(TERM0)
R_(SNS)
(1)
Table 10 shows the termination current settings for three sensing resistors.
Table 10. Termination Current Settings for 55-mΩ, 68-mΩ, 100-mΩ Sense Resistors
BIT
V_I(TERM2)
V_I(TERM1)
V_I(TERM0)
Offset
V_I(TERM) (mV)
13.6
6.8
3.4
3.4
I_(TERM) (mA)
R_(SNS) = 55mΩ
247
124
62
62
I_(TERM) (mA)
R_(SNS) = 68mΩ
200
100
50
50
I_(TERM) (mA)
R_(SNS) = 100mΩ
136
68
34
34
For example, with a 68-mΩ sense resistor, V_(ITERM2)=1, V_(ITERM1)=0, and V_(ITERM0)=1, I_TERM = [ (13.6mV x 1) +
(6.8mV x 0) + (3.4mV x 1) + 3.4mV ] / 68mΩ = 200mA + 0 + 50mA + 50mA = 300mA.
The charge current step (I_{O(CHARGE_STEP)}) is calculated using Equation 2:
I_{O(CHARGE_STEP)}
=
V_I(CHRG0)
R_(SNS)
(2)
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