LTC3440 Datasheet, PDF (15/20 Pages) Linear Technology – Micropower Synchronous Buck-Boost DC/DC Converter

APPLICATIO S I FOR ATIO
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.
LTC3440
INPUT_VOLTAGE
V1
C1
10μF
FB_PIN
Q1
2N3906
R1
0.5Ω
VIN_PIN
Figure 10. Simple Input Current Control
Utilizing the Voltage Loop
TYPICAL APPLICATIO S
3-Cell to 3.3V at 600mA Converter
L1
4.7μH
D1
V_IN = 2.7V TO 4.5V
3
SW1
4
SW2
7
LTC3440
6
V_IN
V_OUT
8
SHDN/SS
9
FB
+
3 CELLS
2
10
C1 *
MODE/SYNC V_C
10μF ₁
R_T
5
GND
R_T
45.3k
f_OSC
=
1.5MHz
D2
C3
33pF
R1
R5
340k 10k
C4 150pF
R3 15k
R2
200k
C5 10pF
V_OUT
3.3V
600mA
C2
22μF
*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY
C1: TAIYO YUDEN JMK212BJ106MG
C2: TAIYO YUDEN JMK325BJ226MM
D1, D2: CENTRAL SEMICONDUCTOR CMDSH2-3
L1: SUMIDA CDR43-4R7M
3440 TA03a
3-Cell to 3.3V Efficiency
100
90 _{Burst Mode}
80 ^OPERATION
70
V_IN = 2.7V
60
V_IN = 4.5V
50
40
V_IN = 3.3V
30
20
10
0 ^{fOSC = 1.5MHz}
0.1
1
10
100
OUTPUT CURRENT (mA)
1000
3440 TA03b
3440fb
15