Datasheet

15
LTC3440
3440fb
Figure 10. Simple Input Current Control
Utilizing the Voltage Loop
APPLICATIO S I FOR ATIO
WUUU
TYPICAL APPLICATIO S
U
3-Cell to 3.3V at 600mA Converter
SW1
V
IN
SHDN/SS
MODE/SYNC
R
T
SW2
V
OUT
FB
V
C
GND
3
7
8
2
1
4
6
9
10
5
LTC3440
L1
4.7μH
D1
R3 15k
R5
10k
R1
340k
R2
200k
3440 TA03a
R
T
45.3k
f
OSC
= 1.5MHz
C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ226MM
D1, D2: CENTRAL SEMICONDUCTOR CMDSH2-3
L1: SUMIDA CDR43-4R7M
*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY
C1
10μF
3 CELLS
V
IN
= 2.7V TO 4.5V
*
C4 150pF
C3
33pF
D2
C5 10pF
C2
22μF
V
OUT
3.3V
600mA
+
OUTPUT CURRENT (mA)
30
EFFICIENCY (%)
90
100
20
10
80
50
70
60
40
0.1 10 100 1000
3440 TA03b
0
1
Burst Mode
OPERATION
V
IN
= 2.7V
V
IN
= 3.3V
f
OSC
= 1.5MHz
V
IN
= 4.5V
3-Cell to 3.3V Efficiency
INPUT_VOLTAGE
FB_PIN
VIN_PIN
Q1
2N3906
R1
0.5Ω
C1
10μF
V1
Simple Average Input Current Control
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 V
C
voltage does not slam. The averag-
ing function of current comes from the fact that voltage
loop compensation is also used with this circuit.