AAT3110IJS-4.5-T1 AAT [Advanced Analog Technology, Inc.], AAT3110IJS-4.5-T1 Datasheet - Page 12

• Manufacturer Part Number: AAT3110IJS-4.5-T1
• Manufacturer: AAT [Advanced Analog Technology, Inc.]

Functional Block Diagram
Functional Description
Operation
The AAT3110 uses a switched capacitor charge
pump to boost an input voltage to a regulated output
voltage. Regulation is achieved by sensing the
charge pump output voltage through an internal
resistor divider network. A switched doubling circuit
is enabled when the divided output drops below a
preset trip point controlled by an internal comparator.
The charge pump switch cycling enables four inter-
nal switches at two non-overlapping phases. During
the first phase, switches S1 and S4 are switched on
(short) and switches S2 and S3 are off (open). The
flying capacitor C
mately equal to input voltage V
phase, switches S1 and S4 are turned off (open) and
switches S2 and S3 are turned on (short). The low
side of the flying capacitor C
during the first phase. During the second phase, the
flying capacitor C
is connected to V
the flying capacitor C
and is connected to output through a switch. For
each cycle phase, charge from input node V
transported from a lower voltage to a higher voltage.
This cycle repeats itself until the output node voltage
is high enough to exceed the preset input threshold
of the control comparator. When the output voltage
exceeds the internal trip point level, the switching
12
(Refer to block diagram)
FLY
FLY
IN
. The voltage at the high side of
is switched so that the low side
is charged to a level approxi-
FLY
is bootstrapped to 2
SHDN
FLY
VIN
IN
is connected to GND
. During the second
CONTROL
IN
+
-
V
IN
is
MicroPower™ Regulated Charge Pump
V
REF
cycle stops and the charge pump circuit is tem-
porarily placed in an idle state.
AAT3110 has a quiescent current of 13µA or less.
The closed loop feedback system containing the
voltage sense circuit and control comparator allows
the AAT3110 to provide a regulated output voltage to
the limits of the input voltage and output load cur-
rent. The switching signal, which drives the charge
pump, is created by an integrated oscillator within
the control circuit block. The free-running charge
pump switching frequency is approximately 750kHz.
The switching frequency under an active load is a
function of V
For each phase of the switching cycle, the charge
transported from V
by the following formula:
The relative average current that the charge pump
can supply to the output may be approximated by
the following expression:
The AAT3110 has complete output short-circuit and
thermal protection to safeguard the device under
extreme operating conditions. An internal thermal
protection circuit senses die temperature and will shut
down the device if the internal junction temperature
exceeds approximately 145°C. The charge pump will
remain disabled until the fault condition is relieved.
S2
S4
GND
I
OUT(AVG)
V
PHASE
S3
IN
, V
C
OUT
FLY
IN
C
C+
C-
VOUT
, C
FLY
to V
OUT,
(2
OUT
(2
and I
V
can be approximated
IN
V
- V
OUT
IN
AAT3110
- V
OUT
.
When idle, the
OUT
3110.2005.11.1.4
)
)
F
SW