BQ24105-Q1 Datasheet, PDF (20/35 Pages) Texas Instruments – SYNCHRONOUS SWITCHMODE, LI-ION AND LI-POLYMER CHARGE-MANAGEMENT IC WITH INTEGRATED POWER FETs ( bqSWITCHER™)

bq24105-Q1
SLUS953 – AUGUST 2009................................................................................................................................................................................................. www.ti.com
Current Sense Amplifier
A current sense amplifier feature that translates the charge current into a DC voltage is offered. Figure 11 is a
block diagram of this feature.
OUT
R_SNS
SNS
+
K_ISET2
-
BAT
-
+
+
FASTCHG
-
Disable
ISET2
R_ISET2
Figure 11. Current Sense Amplifier
The voltage on the ISET2 pin can be used to calculate the charge current. Equation 12 shows the relationship
between the ISET2 voltage and the charge current:
I_CHARGE
+
V_ISET2
R_SNS
K_(ISET2)
R_ISET2
(12)
This feature can be used to monitor the charge current (Figure 12) during the current regulation phase
(Fastcharge only) and the voltage regulation phase. The schematic for the application circuit for this waveform is
shown in Figure 14
CH3 = Inductor Current
CH3
500 mA/div
CH1 = ISET2
CH3
0A
CH1
200 mV/div
CH2
10 V/div
CH2 = OUT
CH1
0V
CH2
16 V
t = Time = 200 ms/div
Figure 12. Current Sense Amplifier Charge Current Waveform
20
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