Datasheet

Data Sheet ADP1621
Rev. B | Page 25 of 32
Low Input and High Output Boost Converter
Figure 36 shows a typical application boost converter circuit
that operates at a switching frequency of 200 kHz with V
IN
= 5 V
and V
OUT
= 30 V with a 1 A load. The duty cycle for this circuit
is about 83%. A higher switching frequency can be selected, but
the switching power loss in the MOSFET increases and a bigger
MOSFET is needed. For switch-node voltages greater than 30 V,
a sense resistor, R
CS
, is needed because the absolute maximum
voltage at CS is 33 V.
High Input Voltage Boost Converter Circuit
Input voltages higher than 5.5 V are possible with the addition
of a resistor and an NPN transistor, as shown in Figure 37, or just
with a single resistor, as shown in Figure 38. When there is a
wide input voltage range, it is sometimes desirable to use the
pass NPN transistor, as shown in Figure 37. If the input voltage
range is narrow, a single resistor connecting to the IN and PIN
pins is sufficient, as shown in Figure 38. In Figure 37, Resistor R3
limits the current going into IN, and there is power loss in this
resistor. The voltages at IN and PIN are both clamped to about
5.5 V, which can rise to as high as 5.9 V when the shunt current
is 30 mA. Refer to Figure 9 for the I-V characteristics of the
shunt regulators. Ensure that Resistor R3 is physically large
enough to handle the power dissipation. For switch-node
voltages higher than 30 V, a current-sense resistor is needed and
the CS pin senses the voltage across the sense resistor.
ADP1621
PIN
GATE
CS
AGND
PGND
SDSN
COMP
FREQ
GND
IN
FB
R1
115kΩ
1%
R2
4.87kΩ
1%
C1
47µF
6.3V
×2
L1
7.8µH
M1
C
COMP
20pF
f
OSC
= 200kHz
C1 = MURATA GRM31CR60J476M
C
OUT1
= MURATA GRM31CR72A10
C
OUT2
= MURATA GRM55ER71H475K
C
OUT3
= RUBYCON 50ZL330M10x23
M1 = VISHAY SUD50N06-07L
D1 = IRF 15TQ060
L1 = COILCRAFT DO501DH-782ML
R
S
909Ω
R
CS
3mΩ
R
FREQ
100kΩ
1%
D1
C3
1µF
10V
C4
0.1µF
10V
C2
120pF
R
COMP
1.6MΩ
V
IN
= 5V
C
OUT1
1µF
100V
C
OUT2
4.7µF
50V
C
OUT3
330µF
50V
×2
V
OUT
= 30V
1A
06090-035
Figure 36. Low Input, High Output Boost Converter
ADP1621
PIN
GATE
CS
AGND
PGND
SDSN
COMP
FREQ
GND
IN
FB
R1
115kΩ
1%
R3
700Ω
R2
4.87kΩ
1%
C1
22µF
16V
×2
L1
8.2µH
M1
C
COMP
220pF
f
OSC
= 560kHz
C1 = MURATA GRM32ER61C226K
C
OUT1
= MURATA GRM31CR72A105K
C
OUT2
= MURATA GRM55ER71H475K
C
OUT3
= RUBYCON 50ZL220M10x23
M1 = IRF7470
Q1 = SIGNAL NPN TRANSISTOR
D1 = MBRB7H50
L1 = COILCRAFT MSS1260-822ML
R
S
402Ω
R
CS
3mΩ
R
FREQ
34.8kΩ
D1
Q1
C4
0.1µF
10V
C3
1µF
10V
C2
120pF
R
COMP
2MΩ
V
IN
= 8V TO 15V
C
OUT1
1µF
100V
C
OUT2
4.7µF
50V
C
OUT3
330µF
50V
×2
V
OUT
= 30V
1A
06090-036
Figure 37. High Input Voltage and High Output Voltage Converter