Triple-Output Charge Pump Regulator
Functional Block Diagram
C+
C-
AAT2820
Soft Start
EN
1MHz
Oscillator
2X Charge
Pump
OUT
IN
V
REF
Reference
Oscillator
EN/PN
Control
Logic
Charge
Pump
DVRP
DVRN
FBP
REF
Over-
Temperature
Protection
V
REF
FBN
GND
Functional Description
5V Regulated Output
The main power supply is a charge pump doubler
architecture used to support the high-current
demand required by the application. Charge pump
regulation is achieved by sensing the output volt-
age through an internal resistor divider network. A
switch doubling circuit is enabled when the divided
output drops below a preset trip point controlled by
an internal comparator. The free-running charge
pump switching frequency is approximately 1MHz.
The charge pump is designed to deliver 150mA of
continuous current (loads greater than the maxi-
mum load condition may cause permanent dam-
age to the device).
pumps. Using a single stage, the first charge pump
inverts the supply voltage (V
IN
) and provides a reg-
ulated negative output voltage. The second charge
pump doubles V
IN
and provides a regulated posi-
tive output voltage. These outputs use external
Schottky diodes and capacitor multiplier stages (as
many as required) to regulate up to ±25V. A con-
stant switching frequency of 1MHz minimizes the
output ripple and capacitor size.
Negative Charge Pump Regulator
During the first half-cycle, the P-channel MOSFET
turns on and the flying capacitor C11 charges to
V
IN
minus a diode drop (Figure 1). During the sec-
ond half-cycle, the P-channel MOSFET turns off
and the N-channel MOSFET turns on, level shifting
C11. This connects C11 in parallel with the output
reservoir capacitor C23. If the voltage across C23
minus a diode drop is less than the voltage across
C11, current flows from C11 to C23 until the diode
turns off.
9
Dual Charge Pump Regulators
The dual charge pump provides low-power regu-
lated output voltages from two individual charge
2820.2006.04.1.4
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
