ame7720 AKM Semiconductor, Inc., ame7720 Datasheet - Page 8

• Manufacturer Part Number: ame7720
• Description: Step-up/step-down 60ma Regulated Charge Pump - Asahi Kasei Microsystems
• Manufacturer: AKM Semiconductor, Inc.

n Shutdown Mode
device into an energy-saving shutdown mode. In this mode,
the output is disconnected from the input as long as V
greater than or equal to minimum V
current is reduced to 1 A maximum.
n Capacitor Selection
C
capacitors generally have a higher Effective Series Resis-
tance (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
also be surface-mount ceramic types. In all cases, X7R or
X5R dielectric are recommended.
0.1 F pump capacitor (C
and output capacitor (C
be used. To minimize output voltage ripple, increase
the output capacitor, C
8
AME7720 / 7721
regulated output voltages ranging from less than the output
to greater than the output. This is accomplshed by auto-
matic mode switching within the device.
down circuit that continuously monitors the IC junction tem-
perature. If the thermal protection circuit senses the die
temperature exceeding approximately 160
shutdown will disable the charge pump switching cycle op-
eration, The thermal limit system has 20
teresis before the charge pump can reset. Once the over
current event is removed from the output and the junction
temperature drops below 140
become active again. The thermal protection system will
cycle on and off if an output short circuit condition persists.
This will allow the AME7720 / 7721 to operate indefinitely a
short circuit condition without damage to the device.
n Detailed Description
n Short Circuit and Thermal
OUT
The AME7720 / 7721 regulated charge pump provides a
The AME7720 / 7721 has a thermal protection and shut-
For minimum output voltage ripple, the output capacitor
A control pin on the regulator can be used to place the
With light loads or higher input voltage, a smaller
Protection
should be a ceramic, surface-mount type. Tantalum
AME, Inc.
OUT
IN
PUMP
, to 10 F or larger.
and C
IN
O
) and smaller 1 F input
C, the charge pump will the
, C
OUT
PUMP
, respectively) can
IN
respecvively) should
and input quiescent
O
C of system hys-
O
C, the thermal
IN
is
60mA Regulated Charge Pump
n Efficiency
with the output voltage version, the applied input volt-
age, the load current, and the internal operation mode
of the device.
n Layout
To minimized both input and output ripple, keep the
capacitors as close as possible to the regulator using
short, direct circuit traces.
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.
The approximate efficiency is given by:
The trace lengths from the input and output capaci-
5V Version (V
Efficiency (%) = V
3.3V Version (V
Efficiency (%) = V
Large ripple currents flow in the V
The efficiency of the charge pump regulator varies
IN
<= V
IN
Step-Up/Step-Down
> V
OUT
OUT
OUT
OUT
/ 2V
/ V
)
)
IN
IN
¡D 100
¡D 100
IN
and V
OUT
traces.