bq2056/T/V
R3
Q1
4.7K
2N3906
2TX788B
Q2
5 VDC
D1
DC+
1N5817
R5
2.7K
R5
2K
C2
DC-
0.1 F
1
8
7
6
5
INH
VCC
CC
2
BAT+
BAT-
TRKL
3
C1
10 F
10V
VS
BAT
SNS
4
COMP
bq2056
R2 1K
R6
0.3
R1
1K
bq2056sc.eps
Figure 1. Low-Dropout Single-Cell Li-Ion Charger
is accomplished by comparing pin BAT voltage to the in-
ternal threshold VMIN. While pin BAT voltage is less
than VMIN and pin INH is low, the open-drain output
TRKL is driven low and the voltage/current regulator is
disabled (CC=high-Z). In the bq2056V, low-voltage de-
tection occurs when the voltage on pin BAT is less than
or equal to VMIND. As shown in Figure 1, TRKL enables
an external trickle-charge circuit to bring the battery
voltage up to VMIN or VMIND.
Functional Description
The bq2056 supports a precision current- and voltage-
limited charging system for Li-Ion batteries. The no-load
voltage regulation references (VREG) for the bq2056 and
bq2056T are maintained at 4.1V and 8.2V, respectively.
The bq2056V provides variable regulation to accommo-
date a wide range of charge voltages and may be used to
meet tighter tolerance requirements through external
trimming. The functional block diagram for the bq2056
is on the first page of this data sheet, and Figure 1 illus-
trates a typical application.
Current Regulation
The bq2056 provides current regulation while the pack
voltage is below the voltage limit. Charge-current feed-
back, applied through pin SNS, maintains regulation
around a threshold of VSNS. The following formula calcu-
lates the value of the sense-resistor connected in series
with the negative terminal of the battery pack (Figure 3):
Charge Algorithm
The bq2056 completes the charge cycle in two phases. A
constant current phase replenishes approximately 70%
of battery capacity, while an accurate voltage regulation
phase completes the charge.
RSNS= 0.1/ IMAX
Figure 2 shows a typical charge algorithm for bq2056,
including charge qualification, current regulation, and
voltage regulation phases.
where IMAX is the maximum charging current. IMAX
should not exceed 1A.
An external PNP or power P-FET may be used as the se-
ries pass element with control provided through output
pin CC.
Charge Qualification
During charge qualification the bq2056 detects a low
battery and reports this status on pin TRKL. Detection
3
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