PM6685 STMicroelectronics, PM6685 Datasheet - Page 37

• 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
where ΔIL is the inductor current ripple and VRIPPLE is the overall ripple of the T node
voltage. It should be chosen higher than approximately 30mV.
The stability of the system depends firstly on the output capacitor value and on RTOT:
Equation 27
The following condition should be satisfied:
Equation 28
Where k is a free design parameter greater than 3 and determines the minimum integrator
capacitor value CINT:
Equation 29
In order to ensure stability it must be also verified that:
Equation 30
C must be selected as shown:
Equation 31
R must be chosen in order to have enough ripple voltage on integrator input:
Equation 32
R1 can be selected as follows:
Doc ID 11674 Rev 8
f
C
sw
INT
C
>
INT
R
k
>
TOT
×
2
>
R
f
π
C
Z
2
=
×
>
=
=
π
⎛
⎜
⎝
R
R
g
5
g
×
2
f
sw
ESR
k
m
m
ESR
π
×
f
Zout
L
×
C
−
C
INT
×
+
f
Z
×
out
C
R
k
⎞
⎟
⎠
V
out
×
×
Vr
OUT
R
V
Vr
OUT
TOT
Monitoring and protections
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