AME, Inc.
AME7730
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Detailed Description
The AME7730 uses charge pump voltage doubler struc-
ture to boost an input voltage to a regulated output volt-
age. Regulation is achieved by decting the charge pump
output voltage through an internal resistor divider network.
A charge pump circuit is enabled when the divided output
voltage below a preset trip point controlled by an internal
comparator.
100mA Regulated Charg Pump
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Capacitor Selection
For minimum output voltage ripple, the output capaci-
tor C
OUT
should be a ceramic, surface-mount type. Tan-
talum capacitors generally have a higher Effective Series
Resistance (ESR) and may contribute to higher output
voltage ripple. Leaded capacitors also increase ripple
due to the higher inductance of the package itself. To
achieve best operation with low input voltage and high
load current, the input and pump capacitors (C
IN
, C
PUMP
respectively) should also be surface-mount ceramic types.
In all cases, X7R or X5R dielectric are recommended.
With ligh loads or higher input voltage, a smaller 0.1µF
pump capacitor (C
PUMP
) and smaller 1µF input and output
capacitor (C
IN
and C
OUT
respectively) can be used. To
minimize output voltage ripple, increase the output ca-
pacitor C
OUT
to 10µF or larger.
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Short Circuit and Thermal
Protection
The AME7730 has a thermal protection and shutdown
circuit that continuously monitors the IC junction tem-
perature. If the thermal protection circuit senses the die
temperature exceeding approximately 160
o
C, the ther-
mal shutdown will disable the charge pump switching
cycle operation, the thermal limit system has 20
o
C of
system hysteresis before the charge pump can reset.
Once the over current event is removed from the output
and the junction temperature drops below 140
o
C, the
charge pump will the become active again. The thermal
protection system will cycle on and off if an output short
circuit condition persists. This will allow the AME7730
to operate indefinitely a short circuit condition with out
damage to the device.
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Efficiency
The efficiency of the charge pump regulator depends
on the applied input voltage, the load current, and the
internal operation mode of the device.
The approximate efficiency is given by:
Efficiency (%) = V
OUT
/ 2V
IN
．
100 %
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Shutdown Mode
A control pin EN on the regulator can be used to place
the device into an energy-saving shutdown mode. In this
mode, the output is disconnected from the input as long
as V
IN
is greater than or equal to minimum V
IN
and input
quiescent current is reduced to 1µA maximum.
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Layout
Large ripple currents flow in the V
IN
and V
OUT
traces. To
minimize both input and output ripple, keep the capaci-
tors as close as possible to the regulator using short,
direct circuit traces.
The trace lengths from the input and output capacitors
have been kept as short as possible. A star ground sys-
tem has been implemented, with GND pin as the center
of the star. No ground plane is provided in other layers as
this will provide capacitive coupling for noise spikes.
6
Rev.A.01
AME [ ANALOG MICROELECTRONICS ]
