PM6685 STMicroelectronics, PM6685 Datasheet - Page 33

• 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
8.10
Power MOSFETs
Logic-level MOSFETs are recommended, since low side and high side gate drivers are
powered by LDO5. Their breakdown voltage VBR
In notebook applications, power management efficiency is a high level requirement. The
power dissipation on the power switches becomes an important factor in switching
selections. Losses of high-side and low-side MOSFETs depend on their working conditions.
The power dissipation of the high-side MOSFET is given by:
Equation 16
Maximum conduction losses are approximately:
Equation 17
where RDSon is the drain-source on resistance of the high side MOSFET.
Switching losses are approximately:
Equation 18
where ton and toff are the switching times of the turn off and turn off phases of the MOSFET.
As general rule, high side MOSFETs with low gate charge are recommended, in order to
minimize driver losses.
Below there is a list of possible choices for the high side MOSFET.
Table 14.
The power dissipation of the low side MOSFET is given by:
Equation 19
Maximum conduction losses occur at the maximum input voltage:
Manufacturer
P
switching
ST
ST
High side MOSFET manufacturer
=
V
IN
×
I (
LOAD
STS12NH3LL
STS17NH3LL
P
conduction
(max)
Type
P
Doc ID 11674 Rev 8
DHighSide
2
−
P
=
Δ
DLowSide
2
I
R
L
DSon
)
=
×
P
t
on
conduction
×
Gate charge (nC)
=
×
V
V
P
f
IN
sw
OUT
conduction
min
DSS
+
10
18
+
×
V
P
I
IN
must be higher than VINmax.
LOAD
switching
×
I (
LOAD
(max)
Monitoring and protections
(max)
2
Rated reverse voltage (V)
2
+
Δ
2
I
L
)
×
30
30
t
off
×
f
sw
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