PM6641 STMicroelectronics, PM6641 Datasheet - Page 38

• 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

Components selection
8.4
38/47
If ceramic capacitors are used, the output voltage ripple due to inductor current ripple is
negligible. Then the inductance could be smaller, reducing the size of the choke. In this case
it is important that output capacitor can adsorb the inductor energy without generating an
overvoltage condition when the system changes from a full load to a no load condition.
The minimum output capacitance can be chosen by the following equation:
Equation 21
where V
voltage before the load transient.
SW regulator compensation components selection
As described in section SW regulators control loop , the PM6641 switching regulators control
loop is:
Equation 22
If the output capacitor C
frequency zero,
Equation 23
This pole is useful if the f
However, the first assumption must relate the cross-over frequency, f
loop gain:
Equation 24
G
LOOP
f
(
is the output capacitor voltage after the load transient and V
2 j
π
G
f
CO
LOOP
)
f
≅
zo
(
g
) s
=
m
K
=
1
L
g
O
2
α
zo
m
π
and its equivalent series resistance (ESR) R
K
C
2
zero is greater than about
π
L
O
f
α
R
CO
Doc ID 13510 Rev 3
ES
sC
C
C
C
C
OUT
2
⎛
⎜
⎜
⎝
, the roll-off compensation pole must be added:
⋅
2
sC
π
f
PRO
(
π
f
sC
CO
,
f
min
Ro
CO
C
C
R
≅
C
R
=
C
C
O
R
C
2
L
+
π
(
C
R
+
⋅
Vf
C
I
C
ES
C
2
1
RO
1
LOAD
2
)
Ro
C
−
+
R
R
Vi
+
C
,
MAX
1
O
2
⎞
⎟
⎟
⎠
f
C
)
⋅
0
R
sC
5
O
(
O
=
.
sC
(
g
R
m
O
ES
K
R
L
ES
+
α
i
CO
R
is the output capacitor
2
+
ES
O
, with the control
π
1
f
)
)
CO
provide a low
+
1
C
R
R
O
O
C
(
R
R
ES
O
PM6641
+
R
O
)