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A7801E6R 参数 Datasheet PDF下载

A7801E6R图片预览
型号: A7801E6R
PDF下载: 下载PDF文件 查看货源
内容描述: [DC-DC CONVERTER LOW NOISE, REGULATED CHARGE PUMP]
分类和应用: DC-DC转换器
文件页数/大小: 10 页 / 266 K
品牌: AITSEMI [ AiT Semiconductor ]
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A7801  
AiT Semiconductor Inc.  
DC-DC CONVERTER  
www.ait-ic.com  
LOW NOISE, REGULATED CHARGE PUMP  
DETAILED INFORMATION  
Operation  
The A7801 use a switched capacitor charge pump to boost VIN to a regulated output voltage. Regulation is  
achieved by sensing the output voltage through an internal resistor divider and modulating the charge pump  
output current based on the error signal. A 2-phase non overlapping clock activates the charge pump  
switches. The flying capacitor is charged from VIN on the first phase of the clock. On the second phase of the  
clock it is stacked in series with VIN and connected to VOUT. This sequence of charging and discharging the  
flying capacitor continues at a free running frequency of 0.4MHz (typ). In shutdown mode all circuitry is turned  
off and the A7801 draw only leakage current from the VIN supply. Furthermore, VOUT is disconnected from VIN.  
The EN pin is a CMOS input with a threshold voltage of approximately 0.8V. The A7801 is in shutdown when  
a logic low is applied to the EN pin. Since the EN pin is a high impedance CMOS input it should never be  
allowed to float. To ensure that its state is defined it must always be driven with a valid logic level.  
Short-Circuit Protection  
The A7801 have built-in short-circuit current limiting. During short-circuit conditions, they will automatically  
limit their output current to approximately 300mA.  
Soft-Start  
The A7801 have built-in soft-start circuitry to prevent excessive current flow at VIN during start-up. The  
soft-start time is preprogrammed to approximately 1ms, so the start-up current will be primarily dependent  
upon the output capacitor.  
VIN, VOUT Capacitor Selection  
The style and value of capacitors used with the A7801 determine several important parameters such as  
regulator control loop stability, output ripple, charge pump strength and minimum start-up time. To reduce  
noise and ripple, it is recommended that low ESR (< 0.1Ω) ceramic capacitors be used for both CIN and COUT  
.
These capacitors should be 2.2uF or greater. Tantalum and aluminum capacitors are not recommended  
because of their high ESR. The value of COUT directly controls the amount of output ripple for a given load  
current. Increasing the size of COUT will reduce the output ripple at the expense of higher minimum turn on  
time and higher start-up current. The peak-to-peak output ripple is approximately given by the expression:  
REV1.0  
- JAN 2015 RELEASED -  
- 6 -