PM6685 STMicroelectronics, PM6685 Datasheet - Page 35

• Manufacturer Part Number: PM6685
• Description: IC CTLR DUAL SYNC STDN 5X5VFQFPN
• Manufacturer: STMicroelectronics

Specifications of PM6685

• Applications: Controller, Notebook Power System
• Voltage - Input: 6 ~ 28 V
• Number Of Outputs: 2
• Voltage - Output: -3.3V, 5V
• Operating Temperature: 0°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 32-VFQFN, 32-VFQFPN
• Output Voltage: 5 V, 3.3 V
• Output Current: 0.1 A
• Input Voltage: 5.5 V to 28 V
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 125 C
• Minimum Operating Temperature: - 10 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

PM6685
Figure 36. Circuitry for output ripple compensation
The stability of the system depends firstly on the output capacitor zero frequency. The
following condition should be satisfied:
Equation 21
where k is a design parameter greater than 3 and Rout is the ESR of the output capacitor. It
determinates the minimum integrator capacitor value CINT:
Equation 22
where gm=50us is the integrator transconductance.
In order to ensure stability it must be also verified that:
Equation 23
In order to reduce ground noise due to load transient on the other section, it is
recommended to add a resistor RINT and a capacitor Cfilt that, together with CINT, realize a
low pass filter (see
times) than the switching frequency of the section:
Figure 36
). The cutoff frequency fCUT must be much greater (10 or more
C
Doc ID 11674 Rev 8
f
sw
INT
C
>
>
INT
k
×
2
π
>
f
Zout
×
2
⎛
⎜
⎝
π
f
=
sw
k
g
g
×
m
m
f
2
Zout
−
π
f
×
Zout
C
×
out
V
k
⎞
⎟
⎠
Vr
OUT
×
×
V
R
Vr
OUT
out
Monitoring and protections
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