AIC1845 ETC2 [List of Unclassifed Manufacturers], AIC1845 Datasheet - Page 8

• Manufacturer Part Number: AIC1845
• Description: Regulated 5V Charge Pump In SOT-23
• Manufacturer: ETC2 [List of Unclassifed Manufacturers]

APPLICATION INFORMATION
Introduction
AIC1845 is a micropower charge pump DC/DC
converter that produces a regulated 5V output
with an input voltage range from 2.7V to 5.0V. It
utilizes the charge pump topology to boost V
a regulated output voltage. Regulation is obtained
by sensing the output voltage through an internal
resistor divider. A switched doubling circuit
enables the charge pump when the feedback
voltage is lower than the trip point of the internal
comparator, and vice versa. When the charge
pump is enabled, a two-phase non-overlapping
clock activates the charge pump switches. To
maximize battery life for a battery-used application,
quiescent current is limited up to 13µA.
Operation
This kind of converter uses capacitors to store
and transfer energy. Since the capacitors can’t
change their voltage level abruptly, the voltage
ratio of V
Capacitive voltage conversion is obtained by
switching a capacitor periodically. It first charges
the capacitor by connecting it across a voltage
source and then connects it to the output.
Referring to Fig. 19, during the on state of internal
clock, Q
V
closed. The output voltage is V
2V
IN
V
C
IN
IN
IN
Fig. 19 The circuit of charge pump
.
level. During the off state, Q
1
OUT
and Q
Q3
over V
4
Q1
are closed, which charges C
IN
C1
is limited to some range.
IN
Q4
plus V
Q2
3
and Q
V
C
C1
OUT
OUT
, that is,
2
IN
1
are
to
to
Short Circuit/Thermal Protection
AIC1845 owns a built-in short circuit current
limiting as well as an over temperature protection.
During the short circuit condition, the output
current
approximately 170mA. This short circuit current
will cause a rise in the internal IC junction
temperature. When the die temperature exceeds
150°C, the thermal protection will shut the charge
pump switching operation down and the die
temperature will reduce afterwards. Once the die
temperature drops below 135°C, the charge pump
switching circuit will re-start. If the fault doesn’t
eliminate, the above protecting operation will
repeat again and again. It allows AIC1845 to
continuously work at short circuit condition without
damaging the device.
Shutdown
In shutdown mode, the output is disconnected
from input. The input current gets extremely low
since most of the circuitry is turned off. Due to
high impedance, shutdown pin can’t be floated.
Efficiency
Referring to Fig. 20 and Fig. 21 here shows the
circuit of charge pump at different states of
operation. R
element at conduction. ESR is the equivalent
series resistance of the flying capacitor C
AVE
state and off state, respectively. D is the duty
cycle, which means the proportion the on state
takes. Let’s take advantage of conversation of
charge for capacitor C
capacitor C
amount of charge flowing into C
is equal to that flowing out of C
and I
OFF
is
1
DS-ON
-AVE
has reached its steady state. The
automatically
are the average current during on
is the resistance of the switching
1
. Assume that the
1
at off state.
constrained
1
AIC1845
during on state
1
. I
ON-
8
at