AN001 Datasheet, PDF (2/4 Pages) Analog Intergrations Corporation – Using AIC1628

AN001
design for color LCD brightness contrast bias
control. When V_IN is higher than 7V, a high
efficiency of 93% can be obtained at full load. The
input power can come directly from a battery or
the main power source without requiring
secondary conversion. At the same time it also
provides higher gate drive voltage to the MOSFET,
this result the reducing of MOSFET’s Switch ON
resistance, and hence reduces the conduction
loss directly. All of these factors contribute to the
high conversion efficiency. If an NPN is used for
lower cost consideration, efficiency may be
decreased about 2% to 5%.
The circuit shown in Fig. 3 provides a +12V output
for flash memory programming power. The
efficiency is always in the range of 90% to 95%
when V_IN is in the range from 5V to 11V and the
load is larger than 60mA condition. In other
applications where battery voltage is lower than
5V, the AIC1628 can be configured as the circuit
shown in Fig. 4. Note that the AIC1628 itself is
powered by a 5V main power assumed available.
In this way, it is easier to drive a MOSFET to
obtain a higher efficiency. If cost reduce are
required, the MOSFET can be replaced by an
NPN transistor. Efficiency, however, will also be
reduced by about 2% to 5%.
VIN
C2 ^VREF
SHDN
CL
DHI
DLOW
5V
FB
GND
AIC1628
*Fuse
60mΩ
+5V ~ 24V
VIN
+ _C1
95
120µF
**L1
68µH
90
1N5819
+36V
VOUT
Q1
D1
+
C5
C6
>50mA
85
2SK940
220µF
0.1µF
V_IN=13V
V_IN=9V
V_IN=18V
V_IN=5V
V_OUT=36V
R2
16.5K 0.033µF
C3
(a)
R1
470K ^0.01µF
C4
*Buss Fuse MCR-2A
**Sumida CDR105
80
0
50
100
150
200
Load Current (mA)
(b)
Fig. 2 LCD Contrast Bias Application
(a) Application Circuit
(b) Efficiency vs. Load Current
2