AN001 Datasheet, PDF (1/4 Pages) Analog Intergrations Corporation – Using AIC1628

AN001
A Versatile Step-Up and Step-down Converter Design
Using AIC1628
The AIC1628 step-up DC/DC Converter can
achieve very high efficiency in various
applications, especially for +12V flash memory
programming voltage and color LCD contrast bias
control voltage applications; the efficiency of these
application can reach as high as 85% to 95%.
The greatest concern in systems using battery
power is the power conversion efficiency. High
efficiency converters can not only provide good
power conversion efficiency at normal operation,
but also reduce its own current consumption
during idle time. In order to maintain good
conversion efficiency from light to full loads, the
AIC1628 uses the intermittent switching control
method named PFM (Pulse-Frequency
Modulation) rather than the conventional PWM
control method. Fig. 1 shows the IC’s basic
function block. When the feedback voltage is great
than the reference voltage, the drive output is 0V.
When the feedback voltage is lower than the
reference voltage, the oscillator starting output
and send signal to the driver. This kind of control
method works similar to PWM at full load, with a
stable switch waveform; while light load it uses
intermittent switching to efficiently sustain output
loading requirements.
May 1997
1
VIN
VREF ²
SHDN ³
FB ⁴
PFM
OSCILLATOR
1.22V
REFERENCE
VOLTAGE
CURRENT LIMIT
COMPARATOR
+
-
LATCH
VIN
60mV
VIN
8
CL
7
DHI
OUTPUT DRIVER
6
DLOW
+
-
ERROR COMPARATOR
5
GND
Fig. 1 AIC1628 Function Block
In addition, the AIC1628 converter has the
following features:
1. Able to operate under input voltage range
from 4V to 24V.
2. Output voltage can be adjusted externally.
3. It has a PFM design adjusting switching
frequency and duty cycle automatically,
which makes it possible to obtain highly
efficient conversion over a wide input and
output voltage range.
4. Build in shutdown mode control.
5. Works in high frequency range from 90KHz to
250KHz, hence only requires small size
inductor.
6. It has complementary push-pull output driver,
is able to drive either NPN transistor or
MOSFET.
7. Low cost.
Some application examples are explained below.
The circuit shown in Fig. 2 is a power supply
1