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参数资料
| 型号： | PM6670STR |
| 厂商： | STMICROELECTRONICS |
| 元件分类： | 稳压器 |
| 英文描述： | 3 A SWITCHING CONTROLLER, QCC24 |
| 封装： | 4 X 4 MM, LEAD FREE, VFQFPN-24 |
| 文件页数： | 17/54页 |
| 文件大小： | 742K |
| 代理商： | PM6670STR |
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Device description
PM6670S
24/54
Doc ID 14432 Rev 4
7.1.2
Output ripple compensation and loop stability
The loop is closed connecting the center tap of the output divider (internally, when the fixed
output voltage is chosen, or externally, using the MODE pin in the adjustable output voltage
mode). The feedback node is the negative input of the error comparator, while the positive
input is internally connected to the reference voltage (Vr = 0.9 V). When the feedback
voltage becomes lower than the reference voltage, the PWM comparator goes to high and
sets the control logic, turning on the high-side MOSFET. After the on-time (calculated as
previously described) the system releases the high-side MOSFET and turns on the
synchronous rectifier.
The voltage drop along ground and supply PCB paths, used to connect the output capacitor
to the load, is a source of DC error. Furthermore the system regulates the output voltage
valley, not the average, as shown in Figure 28. Thus, the voltage ripple on the output
capacitor is an additional source of DC error. To compensate this error, an integrative
network is introduced in the control loop, by connecting the output voltage to the COMP pin
Figure 31.
Circuitry for output ripple compensation
The additional capacitor is used to reduce the voltage on the COMP pin when higher than
300 mVpp and is unnecessary for most of applications. The trans conductance amplifier
(gm) generates a current, proportional to the DC error, used to charge the CINT capacitor.
The voltage across the CINT capacitor feeds the negative input of the PWM comparator,
forcing the loop to compensate the total static error. An internal voltage clamp forces the
COMP pin voltage range to ±150 mV with respect to VREF. This is useful to avoid or smooth
output voltage overshoot during a load transient. When the pulse-skip mode is entered, the
clamping range is automatically reduced to 60 mV in order to enhance the recovering
capability. In the ripple amplitude is larger than 150 mV, an additional capacitor CFILT can
be connected between the COMP pin and ground to reduce ripple amplitude, otherwise the
integrator will operate out of its linearity range. This capacitor is unnecessary for most of
applications and can be omitted.
+
-
V
VREF
REF
COMP
g
gm
m
VSNS
R
RFb1
Fb1
R
RFb2
Fb2
Vr
+
PWM
Comparator
C
CINT
INT
R
RINT
INT
C
CFILT
FILT
t
Vr
C
COUT
OUT
COMP PIN
VOLTAGE
OUTPUT
VOLTAGE
I=gm(V1-Vr)
V
V11
t
ΔV
V
VC
CINT
INT
ESR
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| PM6675ATR | 功能描述:低压差控制器 - LDO High eff SD CNRL RoHS:否 制造商:Micrel 最大输入电压:5.5 V 输出电压:Adjustable 输出电流:10 mA 负载调节: 输出类型:Adjustable, Fixed 输出端数量:1 最大工作温度:+ 125 C 安装风格:SMD/SMT 封装 / 箱体:SOT-23-6 |
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