PM6641 STMicroelectronics, PM6641 Datasheet - Page 25

• 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

PM6641
In order to obtain the typical integrative loop transfer function the signal stag e must
compensate for the power stage pole (due to the output capacitor and the load) and zero
(above the loop bandwidth if ceramic output capacitors are selected). The signal stage
transfer function is:
Equation 2
Where g
due to the output resistor divider (0.8 V / Vout). The external compensation network (R
and C
●
●
●
The control loop gain is obtained by multiplying G(s) by H(s):
Equation 3
This model provides good results if the control loop cut-off frequency f
fsw/10.
One zero, to compensate the power stage pole:
One pole in order to delete the static output voltage error;
One pole, if necessary, in order to compensate the high frequency zero due to the
output capacitor ESR:
RO
M
) introduces:
is the power stage transconductance, K
G
LOOP
(
) s
=
g
m
( G
K
L
) s
α
Doc ID 13510 Rev 3
=
sC
g
C
m
C
⎛
⎜
⎜
⎝
K
C
sC
R
L
C
(
sC
α
C
RO
Ro
sC
=
C
R
R
R
C
C
C
C
C
O
⎛
⎜ ⎜
⎝
=
+
sC
(
+
R
C
sC
C
1
C
O
Ro
O
)
Ro
C
R
L
C
+
R
R
ES
is a design parameter and α is the gain
R
+
C
C
ES
1
+
⎞
⎟
⎟
⎠
+
)
C
⋅
1
C
sC
Ro
C
(
O
sC
+
(
R
1
⎞
⎟ ⎟
⎠
O
ES
R
ES
+
R
CO
+
O
1
Device description
)
)
is lower than about
+
1
R
O
c
25/47
, C
c