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PM6670AS 데이터시트(PDF) 23 Page - STMicroelectronics

부품명 PM6670AS
상세설명  Complete DDR2/3 memory power supplies controller
PDF  54 Pages
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제조업체  STMICROELECTRONICS [STMicroelectronics]
홈페이지  http://www.st.com
Logo STMICROELECTRONICS - STMicroelectronics

PM6670AS 데이터시트(HTML) 23 Page - STMicroelectronics

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PM6670AS
Device description
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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 26. 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
through a capacitor (CINT) as shown in Figure 29.
Figure 28. Switching section simplified block diagram
+
-
HS
HS
driver
driver
Level
Level
shifter
shifter
LS
LS
driver
driver
Q
Q
R
S
Ton
Ton--min
min
Anti cross-
conduction
circuitry
Toff
Toff--min
min
Q
R
S
+
-
PWM Comparator
PWM Comparator
Positive Current Limit comparator
Positive Current Limit comparator
0.9V
0.9V
Q
Q
R
S
+
_
Min
Min fsw
fsw
counter
counter
Zero
Zero--crossing
crossing
Comparator
Comparator
bandgap
bandgap
1.236V
1.236V
PHASE
PHASE
PGND
PGND
LGATE
LGATE
BOOT
BOOT
CSNS
CSNS
COMP
COMP
gm
gm
Integrator
Integrator
VSNS
VSNS
VBG
VBG
VBG
VBG
PULSE
PULSE -- SKIP
SKIP
MODE
MODE
MODE<4V
1-Shot generator
Ton
Ton
VSNS
VSNS
VOSC
VOSC
DDRSEL
0.9V
0.9V
100uA
100uA
500mV
2.5V
2.5V
+
-
-
-
+
+
HGATE
HGATE
VREF
VREF
SGND
SGND
VOSC
VOSC
VOSC
VOSC
VCC
VCC



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