PM6641TR STMicroelectronics, PM6641TR Datasheet - Page 39

• Manufacturer Part Number: PM6641TR
• Description: IC CTLR DDR2/3 MONO VR 48VFQFPN
• Manufacturer: STMicroelectronics

Specifications of PM6641TR

• 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
• For Use With: 497-8425 - KIT EVAL PM6641 CHIPSET/DDR2/3
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-6893-2; PM6641TR

PM6641
From the definition of cross-over frequency, the value of the compensation resistor is
derived:
Equation 25
A good choice for the cross-over frequency is to assign f
The fixed parameters g
feedback divider factor (α) is application dependant (see
loop on page 24
After computing R
compensation zero near the power stage pole:
Equation 26
The roll-off capacitance, as said previously, must compensate for the power stage high
frequency zero, when necessary:
Equation 27
As final step, it’s important to verify that the compensation zero is quite far from the cross-
over frequency. An empirical rule is satisfied if the following holds:
Equation 28
All these considerations are true if the cross-over frequency is quite lower than the switching
frequency, and the compensation zero and the power stage pole are far enough from f
section for details).
C
, the compensation capacitor can be designed in order to place the
G
m
LOOP
= 300 μs and K
(
2 j
Doc ID 13510 Rev 3
π
f
CO
f
C
)
ZC
C
=
C
=
1
=
RO
L
⇒
2
C
= 4.4 s are design parameters, whereas the
π
O
R
=
C
(
1
C
C
R
C
R
R
O
O
=
R
C
C
R
+
C
2
ES
≤
π
R
f
ES
CO
f
CO
5
g
C
)
m
CO
Chapter 7.3: SW regulators control
O
K
R (
L
equal to
α
ES
R
O
+
R
O
Components selection
)
f
SW
10
.
CO
39/47
.