PM6685 STMicroelectronics, PM6685 Datasheet - Page 34

• 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
8.11
34/48
Equation 20
Choose a synchronous rectifier with low R
variation of the phase node voltage can bring up even the low side gate through its gate-
drain capacitance CRSS, causing cross-conduction problems. Choose a low side MOSFET
that minimizes the ratio CRSS/CGS (CGS = CISS - CRSS).
Below there is a list of some possible low side MOSFETs.
Table 15.
Dual n-channel MOSFETs can be used in applications with a maximum output current of
about 3 A. Below there is a list of some MOSFET manufacturers.
Table 16.
A rectifier across the low side MOSFET is recommended. The rectifier works as a voltage
clamp across the synchronous rectifier and reduces the negative inductor swing during the
dead time between turning the high-side MOSFET off and the synchronous rectifier on. It
can increase the efficiency of the switching section, since it reduces the low side switch
losses. A schottky diode is suitable for its low forward voltage drop (0.3 V). The diode
reverse voltage must be greater than the maximum input voltage VINmax. A minimum
recovery reverse charge is preferable. Below there is a list of some schottky diode
manufacturers.
Table 17.
Closing the integrator loop
The design of external feedback network depends on the output voltage ripple. If the ripple
is higher than approximately 30 mV, the feedback network (
keep the loop stable.
Manufacturer
Manufacturer
Manufacturer
ST
ST
ST
ST
ST
ST
Low side MOSFET manufacturer
Dual MOSFET manufacturer
Schottky diode manufacturer
STS8DNH3LL
STS4DNF60L
STPS1L30M
STPS1L20M
Type
P
Series
conduction
STS25NH3LL
STS17NF3LL
Type
Doc ID 11674 Rev 8
=
R
Forward voltage
RDSon (mΩ)
DSon
×
25
65
0.34
0.37
DSon
(V)
⎛
⎜
⎜
⎝
RDSon (mΩ)
1
−
. When high side MOSFET turns on, the fast
V
5.5
3.5
V
IN
OUT
max
Gate charge (nC)
⎞
⎟
⎟
⎠
×
Rated reverse
I
LOAD
voltage (V)
Figure 36
0.047
0.011
10
32
(max)
30
20
2
) is usually enough to
Rated reverse voltage
Rated reverse
Reverse current
voltage (V)
0.000075
(V)
30
30
0.00039
30
60
(uA)
PM6685