PM6641 STMicroelectronics, PM6641 Datasheet - Page 24

• Manufacturer Part Number: PM6641
• Description: IC MONO VR DDR2/3 PC VFQFPN-48
• Manufacturer: STMicroelectronics

Specifications of PM6641

• Applications: Converter, DDR2, DDR3
• Voltage - Input: 2.7 ~ 5.5 V
• Number Of Outputs: 3
• Voltage - Output: 0.8 ~ 5.5 V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 48-VFQFN
• Output Voltage: 0.9 V
• Output Current: 3 A
• Input Voltage: 2.7 V to 5.5 V
• Switching Frequency: 1000 KHz
• Operating Temperature Range: - 40 C to + 125 C
• Mounting Style: SMD/SMT
• For Use With: 497-8425 - KIT EVAL PM6641 CHIPSET/DDR2/3
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Device description
7.3
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SW regulators control loop
The PM6641 switching regulators are buck converters employing a constant frequency,
peak current mode PWM control loop, as shown in the following figure:
Figure 28. SW regulator control loop
In the current mode constant frequency loop the power stage is represented by a controlled
current generator feeding the power stage output capacitor and load. The equivalent
transfer function is:
Equation 1
with Co and Res being the output capacitance and its equivalent series resistance and Ro
representing the output load.
( H
) s
C
C
Doc ID 13510 Rev 3
RO
RO
=
K
K
I
I
L
L
L
L
V
I
L
O
(
V
V
(
) s
) s
C
C
R
R
R
R
C
C
C
C
ES
ES
C
C
C
C
O
O
Power Stage
Power Stage
=
sC
Signal Stage
Signal Stage
(
O
sC
R
R
(
R
g
g
O
O
m
m
O
ES
R
ES
+
R
+
O
V
V
1
O
O
V
V
)
)
a
a
REF
REF
+
1
R
O
PM6641