Datasheet

Data Sheet ADP1621
Rev. B | Page 27 of 32
SEPIC CONVERTER CIRCUIT
A single-ended primary inductance converter (SEPIC) topology
is shown in Figure 39. This topology is useful for an unregulated
input voltage, where the regulated output voltage falls within the
input voltage range.
The input and output are dc-isolated by a coupling capacitor,
C5. L1 and L2 are coupled inductors with a 1:1 turn ratio, which
saves space on the PCB. In steady state, the average voltage across
C5 is the input voltage. When the MOSFET turns on and the
diode turns off, the input voltage provides energy to L1, and C5
provides energy to L2. The output capacitor, C
OUT
, supplies the
load current during this time. When the MOSFET turns off and
the diode turns on, the energy in L1 and L2 is released to charge
the output capacitor, C
OUT
, and the coupling capacitor, C5, as
well as to supply current to the load.
LOW VOLTAGE POWER-INPUT CIRCUIT
The ADP1621 can be configured to run from a low voltage
(as low as 1 V) power input. The power source generally needs
to have a high current capability, such as a fuel cell. Figure 40
illustrates such an application, where the voltage of the power
input is 1 V and the voltage of the chip supply to the IN and
PIN pins is provided by an auxiliary low power source.
ADP1621
IN
GATE
PGND
AGND
FB
SDSN
COMP
FREQ
GND
PIN
CS
R1
17.4kΩ
1%
R2
10kΩ
1%
C1
22µF
10V
×2
C5
10µF
10V
X5R
L2
2.4µH
L1
2.4µH
M1
C
COMP
1.2nF
f
OSC
= 325kHz
C1 = MURATA GRM332ER61A226K
C
OUT2
= SANYO POSCAP 6TPE150MI
C5 = MURATA GRM21BR61A106K
L1, L2 = COUPLED INDUCTORS, 1:1 RATIO, BH ELECTRONICS BH510-1006
M1 = VISHAY Si7882DP
D1 = VISHAY SSC53L
R
S
80Ω
C
OUT1
1µF
10V
R
FREQ
65kΩ
C
OUT2
150µF
6.3V
×3
V
OUT
= 3.3V
2A
V
IN
= 3V TO 5.5V
D1
C3
1µF
10V
C4
0.1µF
10V
C2
33pF
R
COMP
26kΩ
06090-038
Figure 39. A SEPIC DC/DC Converter
ADP1621
IN
GATE
PGND
AGND
FB
SDSN
COMP
FREQ
GND
PIN
CS
R1
35.7kΩ
1%
R2
11.5kΩ
1%
C1
100µF
X5R
6.3V
L1
2.2µH
M1
C
COMP
56nF
C
OUT1
1µF
10V
f
OSC
= 600kHz
C1 = MURATA GRM32ER60J107ME20
C
OUT2
= MURATA GRM21BR60J106K
C
OUT3
= SANYO POSCAP 6TPE150MI
M1 = VISHAY Si7882DP
D1 = MBRD835L
L1 = TOKO FDV0630-2R2M
R
S
249Ω
C
OUT2
10µF
6.3V
R
FREQ
31.6kΩ
1%
C
OUT3
150µF
6.3V
×2
V
OUT
= 5V
1A
V
IN
= 1V
V
CC
= 2.9V TO 5.5V
D1
C3
1µF
10V
C4
0.1µF
10V
C2
260pF
R
COMP
9.4kΩ
06090-039
Figure 40. Low Voltage Power-Input Application Circuit