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AAT1153 参数 Datasheet PDF下载

AAT1153图片预览
型号: AAT1153
PDF下载: 下载PDF文件 查看货源
内容描述: 2A降压转换器 [2A Step-Down Converter]
分类和应用: 转换器
文件页数/大小: 20 页 / 686 K
品牌: ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
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PRODUCT DATASHEET  
AAT1153  
2A Step-Down Converter  
Thermal protection completely disables switching when  
internal dissipation becomes excessive. The junction  
over-temperature threshold is 170°C with 10°C of hys-  
teresis. Once an over-temperature or over-current fault  
conditions is removed, the output voltage automatically  
recovers.  
Control Loop  
The AAT1153 is a peak current mode step-down con-  
verter. The current through the P-channel MOSFET (high  
side) is sensed for current loop control, as well as short  
circuit and overload protection. A slope compensation  
signal is added to the sensed current to maintain stabil-  
ity for duty cycles greater than 50%. The peak current  
mode loop appears as a voltage-programmed current  
source in parallel with the output capacitor. The output  
of the voltage error amplifier programs the current mode  
loop for the necessary peak switch current to force a  
constant output voltage for all load and line conditions.  
Internal loop compensation terminates the transconduc-  
tance voltage error amplifier output. For fixed voltage  
versions, the error amplifier reference voltage is inter-  
nally set to program the converter output voltage. For  
the adjustable output, the error amplifier reference is  
fixed at 0.6V.  
Dropout Operation  
When the battery input voltage decreases near the value  
of the output voltage, the AAT1153 allows the main  
switch to remain on for more than one switching cycle  
and increases the duty cycle until it reaches 100%. The  
duty cycle D of a step-down converter is defined as:  
VOUT  
VIN  
D = TON · FOSC · 100%  
· 100%  
Where TON is the main switch on time and FOSC is the  
oscillator frequency. The output voltage then is the input  
voltage minus the voltage drop across the main switch  
and the inductor. At low input supply voltage, the RDS(ON)  
of the P-channel MOSFET increases, and the efficiency of  
the converter decreases. Caution must be exercised to  
ensure the heat dissipated does not exceed the maxi-  
mum junction temperature of the IC.  
Soft Start / Enable  
Soft start limits the current surge seen at the input and  
eliminates output voltage overshoot. The enable pin is  
active high. When pulled low, the enable input (EN)  
forces the AAT1153 into a low-power, non-switching  
state. The total input current during shutdown is less  
than 1A.  
Maximum Load Current  
Current Limit and Over-Temperature  
Protection  
The AAT1153 will operate with an input supply voltage  
as low as 2.5V, however, the maximum load current  
decreases at lower input voltages due to a large IR drop  
on the main switch and synchronous rectifier. The slope  
compensation signal reduces the peak inductor current  
as a function of the duty cycle to prevent sub-harmonic  
oscillations at duty cycles greater than 50%. Conversely  
the current limit increases as the duty cycle decreases.  
For overload conditions, the peak input current is limited  
to 3.5A. To minimize power dissipation and stresses  
under current limit and short-circuit conditions, switch-  
ing is terminated after entering current limit for a series  
of pulses. The termination lasts for seven consecutive  
clock cycles after a current limit has been sensed during  
a series of four consecutive clock cycles.  
w w w . a n a l o g i c t e c h . c o m  
10  
1153.2007.11.1.1