Kingbor Technology Co.,Ltd
TEL:(86)0755-26508846 FAX:(86)0755-26509052
kB3440
APPLICATIONS INFORMATION
Simple Average Input Current Control
INPUT_VOLTAGE
C1
V1
A simple average current limit circuit is shown in
Figure 10. Once the input current of the IC is above
approximately 1A, Q1 will start sourcing current into the
FB pin and lower the output voltage to maintain the
average input current. Since the voltage loop is utilized to
perform average current limit, the voltage control loop is
maintained and the VC voltage does not slam. The averag-
ing function of current comes from the fact that voltage
loop compensation is also used with this circuit.
10µF
R1
0.51
Q1
VIN_PIN
2N3906
FB_PIN
Figure 10. Simple Input Current Control
Utilizing the Voltage Loop
TYPICAL APPLICATION
3-Cell to 3.3V at 600mA Converter
L1
4.7µH
D2
V
OUT
3.3V
600mA
C3
D1
33pF
3
7
8
2
1
4
SW1
SW2
R1
340k
R5
10k
kB3440
V
= 2.7V TO 4.5V
IN
6
V
V
IN
OUT
FB
9
SHDN/SS
C2
22µF
C4 150pF
R3 15k
10
5
+
MODE/SYNC
V
C
*
C1
10µF
3 CELLS
R2
200k
R
GND
= 1.5MHz
T
R
T
f
C5 10pF
OSC
45.3k
*1 = Burst Mode OPERATION C1: TAIYO YUDEN JMK212BJ106MG
0 = FIXED FREQUENCY
C2: TAIYO YUDEN JMK325BJ226MM
D1, D2: CENTRAL SEMICONDUCTOR CMDSH2-3
L1: SUMIDA CDR43-4R7M
3-Cell to 3.3V Efficiency
100
90
Burst Mode
OPERATION
80
70
60
50
40
30
20
10
0
V
= 2.7V
IN
V
= 4.5V
IN
V
= 3.3V
IN
f
= 1.5MHz
1
OSC
0.1
10
100
1000
OUTPUT CURRENT (mA)
15
KINGBOR [ KINGBOR TECHNOLOGY CO ]
