参数资料
型号: L6727
厂商: STMICROELECTRONICS
元件分类: 稳压器
英文描述: 1.5 A SWITCHING CONTROLLER, 350 kHz SWITCHING FREQ-MAX, PDSO8
封装: LEAD FREE, SOP-8
文件页数: 7/34页
文件大小: 974K
代理商: L6727
L6727
Application details
Doc ID 12933 Rev 4
15/34
9
Application details
9.1
Output voltage selection
L6727 is capable to precisely regulate an output voltage as low as 0.8 V. In fact, the device
comes with a fixed 0.8 V internal reference that guarantees the output regulated voltage to
be within ±1 % tolerance over line and temperature variations between 0 °C and +70 °C
(excluding output resistor divider tolerance, when present).
Output voltage higher than 0.8 V can be easily achieved by adding a resistor ROS between
FB pin and ground. Referring to Figure 1, the steady state DC output voltage will be:
where VREF is 0.8V.
9.2
Compensation network
The control loop showed in Figure 6 is a voltage mode control loop. The error amplifier is a
voltage mode type. The output voltage is regulated to the internal reference (when present,
offset resistor between FB node and GND can be neglected in control loop calculation).
Error Amplifier output is compared to oscillator saw-tooth waveform to provide PWM signal
to the driver section. PWM signal is then transferred to the switching node with VIN
amplitude. This waveform is filtered by the output filter.
The converter transfer function is the small signal transfer function between the output of the
EA and VOUT. This function has a double pole at frequency FLC depending on the L-COUT
resonance and a zero at FESR depending on the output capacitor ESR. The DC Gain of the
modulator is simply the input voltage VIN divided by the peak-to-peak oscillator voltage
ΔV
OSC.
The compensation network closes the loop joining VOUT and EA output with transfer
function ideally equal to -Z
F/ZFB.
Figure 6.
PWM control loop
V
OUT
V
REF
1
R
FB
R
OS
-----------
+
=
L
R
C
OUT
ESR
R
F
C
F
C
P
R
FB
C
S
OSC
V
IN
ΔV
OSC
+
_
V
OUT
V
REF
ZF
Z
FB
PWM
COMPARATOR
ERROR
AMPLIFIER
R
S
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相关代理商/技术参数
参数描述
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