PM6685 STMicroelectronics, PM6685 Datasheet - Page 32

• 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

Monitoring and protections
8.9
32/48
A low ESR capacitor is required to reduce the output voltage ripple. Switching sections can
work correctly even with 20 mV output ripple.
However, to reduce jitter noise between the two switching sections it’s preferable to work
with an output voltage ripple greater than 30 mV. If lower output ripple is required, a further
compensation network is needed (see Closing the integrator loop paragraph).
Finally the output capacitor choice deeply impacts on the load transient response (see Load
transient response paragraph). Below there is a list of some capacitor manufacturers.
Table 12.
Input capacitors selection
In a buck topology converter the current that flows into the input capacitor is a pulsed current
with zero average value. The input RMS current of the two switching sections can be roughly
estimated as follows:
Equation 15
Where D1, D2 are the duty cycles and I1, I2 are the maximum load currents of the two
sections.
Input capacitor should be chosen with an RMS rated current higher than the maximum RMS
current given by both sections.
Tantalum capacitors are good in term of low ESR and small size, but they occasionally can
burn out if subjected to very high current during the charge. Ceramic capacitors have
usually a higher RMS current rating with smaller size and they remain the best choice.
Below there is a list of some ceramic capacitor manufacturers.
Table 13.
Manufacturer
PANASONIC
SANYO
TAYIO YUDEN
TAYIO YUDEN
Manufacturer
TDK
Output capacitor manufacturer
Input capacitor manufacturer
SPCAP UD, UE
POSCAP
TPB,TPD
I
Series
CinRMS
UMK325BJ106KM-T10
C3225X5R1E106M
GMK325BJ106MN
Doc ID 11674 Rev 8
=
D
Series
1
×
Capacitor value
I
1
2
150 to 220
150 to 330
×
1 (
(μF)
−
D
1
)
+
D
Capacitor value
2
×
Rated voltage (V)
I
2
2
×
(μF)
10
10
10
1 (
4 to 6.3
4 to 6.3
−
D
2
)
Rated voltage (V)
ESR max (mΩ)
35 to 65
9 to 18
50
25
35
PM6685