PM6675AS STMicroelectronics, PM6675AS Datasheet - Page 40

• Manufacturer Part Number: PM6675AS
• Description: IC CTLR STP DWN HE LDO VFQFPN24
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of PM6675AS

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 1.5V, 0.6 ~ 3.3 V
• Current - Output: ±1A, ±2A
• Frequency - Switching: 33kHz
• Voltage - Input: 4.5 ~ 36 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-VFQFN, 24-VFQFPN
• Power - Output: 2.3W
• For Use With: 497-8426 - KIT EVAL PM6675S HE CTLR 2A REG497-8413 - BOARD EVAL BASED ON PM6675A
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Application information
40/48
Table 14.
In buck converters the power dissipation of the synchronous MOSFET is mainly due to
conduction losses:
Equation 43
Maximum conduction losses occur at the maximum input voltage:
Equation 44
The synchronous rectifier should have the lowest R
MOSFET turns on, high d
through its gate-drain capacitance C
the choice of the low-side MOSFET is a trade-off between on resistance and gate charge; a
good selection should minimizes the ratio C
Below some tested low-side MOSFETs are listed.
Table 15.
Dual N-MOS can be used in applications with low output current.
Figure 16
Table 16.
Manufacturer
Manufacturer
Manufacturer
ST
ST
IR
ST
ST
ST
IR
IR
shows some suitable dual MOSFETs for applications requiring about 3 A.
Evaluated high-side MOSFETs
Evaluated low-side MOSFETs
Suitable dual MOSFETs
STS12NH3LL
STS7NF60L
IRF7811
STS8DNH3LL
Type
STS12NH3LL
STS25NH3LL
IRF7313
IRF7811
P
Type
Type
conduction
V
/d
t
of the phase node can bring up even the low-side gate
R
DSon
=
P
10.5
R
17
RES
DLowSide
9
DSon
(mΩ)
R
R
, causing cross-conduction problem. Once again,
DSon
DSon
⋅
13.5
⎛
⎜
⎜
⎝
25
46
RSS
40
24
1
≅
(mΩ)
Gate charge (Nc)
−
(mΩ)
P
V
conduction
/ C
V
IN
OUT
,
MAX
DSon
GS
12
25
18
where C
Gate charge (nC)
⎞
⎟
⎟
⎠
⋅
as possible. When the high-side
I
0.069
0.011
0.054
LOAD
C
C
GD
GS
10
33
,
MAX
GS
Rated reverse voltage (V)
2
= C
Rated reverse voltage
ISS
- C
Rated reverse
RSS
30
60
30
voltage (V)
(V)
30
30
30
PM6675AS
.
30
30