AME, Inc.
AME7739
Step-Up / Step-Down
60mA Regulated Charge Pump
n
Efficiency
The efficiency of the charge pump regulator varies
with the output voltage version, the applied input volt-
age, the load current, and the internal operation mode
of the device.
The approximate efficiency is given by:
5.5V
,
5V Version (V
IN
<= V
OUT
)
Efficiency (%) = V
OUT
/ 2V
IN
．
100%
Others Version (V
IN
> V
OUT
)
Efficiency (%) = V
OUT
/ V
IN
．
100%
n
Detailed Description
The AME7739 regulated charge pump provides a regulated
input voltages ranging from less than the output to greater
than the input. This is accomplshed by automatic mode switch-
ing within the device.
n
Short Circuit and Thermal
Protection
The AME7739 has a thermal protection and shutdown cir-
cuit that continuously monitors the IC junction temperature.
If the thermal protection circuit senses the die temperature
exceeding approximately 160
O
C, the thermal shutdown will
disable the charge pump switching cycle operation, The ther-
mal limit system has 20
O
C of system hysteresis before the
charge pump can reset. Once the over current event is re-
moved 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 out-
put short circuit condition persists. This will allow the
AME7739 to operate indefinitely a short circuit condition with-
out damage to the device.
n
Layout
Large ripple currents flow in the V
IN
and V
OUT
traces.
To minimized both input and output ripple, keep the
capacitors as close as possible to the regulator using
short, direct circuit traces.
The trace lengths from the input and output capaci-
tors have been kept as short as possible. A star ground
system 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.
n
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.
n
Capacitor Selection
For minimum output voltage ripple, the output capacitor
C
OUT
should be a ceramic, surface-mount type. Tantalum ca-
pacitors 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 in-
ductance 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 dielectric is recom-
mended.
With light loads or higher input voltage, a smaller 0.1µF
pump capacitor (C
PUMP
) and smaller 1µF input and output ca-
pacitor (C
IN
and C
OUT
, respectively) can be used. To minimize
output voltage ripple, increase the output capacitor, C
OUT
, to
10µF or larger.
6
REV. A.01
AME [ ANALOG MICROELECTRONICS ]
