SLUS249B − FEBRUARY 1997 − REVISED DECEMBER 2001
UCC3956
SWITCH MODE LITHIUM ION
BATTERY CHARGE CONTROLLER
APPLICATION INFORMATION
charger operation (continued)
A block diagram of the UCC3956 is shown on the first page of the data sheet, while Figure 1 shows a typical application
circuit for a buck-derived switch-mode charger. The UCC3956 can be used for charging a single cell or multiple cells
in series. If more than three cells are stacked in series, however, a level-shifting gate-drive may be needed to operate
the buck switch. The application circuit charges a 1200-mAh 2-cell stack at a 1C rate.
setting the oscillator frequency
The frequency of operation for the converter is set by picking values for RSET and COSC.
f
OSC
+
3.475
(COSC
)
20pF)
RSET
(5)
The UCC3956 is capable of operating at frequencies higher than 200 kHz. However, the actual operating frequency
of the buck converter is ultimately determined by the usual tradeoffs of size, cost and efficiency. The application circuit
frequency is set at 100 kHz with COSC = 180 pF and RSET = 162 kΩ.
VIN
10 V to 18 V
2.7 k
Ω
7
STAT0
VDD
9
22 kΩ
2.7 kΩ
6
STAT1
CHGENB 1
0.10µF
CHG
162 kΩ
13 RSET
0.15µF
14 CTO
11
180 pF
RG1
20 k
Ω
GND
VAO 18
CS− 3
RSENSE (See Note 1)
0.18Ω
VA− 19
CF1
2.2 nF
RSENSE (See Note 1)
0.18Ω
2 CELL
1200 mAH
5
CHG
VA+ 20
RS2
2.21 kΩ
RS1 12.2 k
Ω
150 mH
OUT 10
RS3 10 kΩ
0.1µF
10 k
Ω
12 COSC
17 IBAT
15 CAO
CS+
REF
4
8
RS4
11k
Ω
CF3
100 pF
RF4
15.0 kΩ
CF4
1 nF
16
CA−
IMIN
2
0.1
µF
10 kΩ
IBULK = 1.2 A
ITRICKLE = 90 mA
fOCS = 100 kHz
Timeout = 120 minutes
RG2 38.3 k
UDG−00127
Figure 1. Typical Charge Cycle Levels
NOTE: 1.
Either high- or low-side current sensing possible.
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