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AME7721 参数 Datasheet PDF下载

AME7721图片预览
型号: AME7721
PDF下载: 下载PDF文件 查看货源
内容描述: 升压/降压型60毫安稳压型电荷泵 [Step-Up/Step-Down 60mA Regulated Charge Pump]
分类和应用:
文件页数/大小: 16 页 / 256 K
品牌: AKM [ ASAHI KASEI MICROSYSTEMS ]
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AME, Inc.  
Step-Up/Step-Down  
60mA Regulated Charge Pump  
AME7720 / 7721  
nDetailed Description  
nEfficiency  
The AME7720 / 7721 regulated charge pump provides a  
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.  
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:  
nShort Circuit and Thermal  
5V Version (VIN<= VOUT  
Efficiency (%) = VOUT / 2VIN 100  
)
Protection  
The AME7720 / 7721 has a thermal protection and shut-  
down circuit that continuously monitors the IC junction tem-  
perature. If the thermal protection circuit senses the die  
temperature exceeding approximately 160OC, the thermal  
shutdown will disable the charge pump switching cycle op-  
eration, The thermal limit system has 20OC of system hys-  
teresis before the charge pump can reset. Once the over  
current event is removed from the output and the junction  
temperature drops below 140OC, 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 AME7720 / 7721 to operate indefinitely a  
short circuit condition without damage to the device.  
3.3V Version (VIN> VOUT  
Efficiency (%) = VOUT / VIN 100  
)
nLayout  
Large ripple currents flow in the VIN and VOUT 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.  
nShutdown Mode  
A control pin 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 VIN is  
greater than or equal to minimum V and input quiescent  
IN  
current is reduced to 1mA maximum.  
nCapacitor Selection  
For minimum output voltage ripple, the output capacitor  
COUT should be a ceramic, surface-mount type. Tantalum  
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 (CIN, CPUMP respecvively) should  
also be surface-mount ceramic types. In all cases, X7R or  
X5R dielectric are recommended.  
With light loads or higher input voltage, a smaller  
0.1mF pump capacitor (CPUMP) and smaller 1mF input  
and output capacitor (CIN and COUT, respectively) can  
be used. To minimize output voltage ripple, increase  
the output capacitor, COUT, to 10mF or larger.  
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