ltc3440 Linear Technology Corporation, ltc3440 Datasheet - Page 15

• Manufacturer Part Number: ltc3440
• Description: Micropower Synchronous Buck-boost Dc/dc Converter
• Manufacturer: Linear Technology Corporation

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