MAX5942BCSE Maxim Integrated, MAX5942BCSE Datasheet - Page 16

• Manufacturer Part Number: MAX5942BCSE
• Description: Power Switch ICs - POE / LAN
• Manufacturer: Maxim Integrated

IEEE 802.3af Power-Over-Ethernet
Interface/PWM Controller for Power Devices
The current-sense (CS) comparator and its associated
logic limit the peak current through the MOSFET.
Current is sensed at CS as a voltage across a sense
resistor between the source of the MOSFET and GND.
To reduce switching noise, connect CS to the external
MOSFET source through a 100Ω resistor or an RC low-
pass filter (Figures 5, 6). Select the current-sense resis-
tor, R
where I
current.
When V
The propagation delay from the time the switch current
reaches the trip level to the driver turn-off time is 180ns.
The MAX5942A/MAX5942B include an internal error
amplifier that can be used to regulate the output volt-
age in the case of a nonisolated power supply (see
Figure 5. Forward Converter
16
______________________________________________________________________________________
25.5kΩ
SENSE
LIMPrimary
CS
V
(36V TO 72V)
IN
> 465mV, the power MOSFET switches off.
according to the following equation:
R
SENSE
R
CL
is the maximum peak primary-side
= 0 465
0.1µF
Current-Sense Comparator
C
.
SS
4.7µF
Internal Error Amplifier
10µF
C
C
/ V
DD
CC
I
LIMPrimary
V
RCL
V
UVLO
SS_SHDN
PGOOD
GATE
V
DD
CC
EE
1N4148
MAX5942
GND
GATE
6
N
T
NDRV
V+
OUT
CS
FB
V-
14
CMHD2003
N
IRF640N
R
Figure 5). Calculate the output voltage using the follow-
ing equation:
where V
Choose R1//R2 << R
resistance of FB. The gain of the error amplifier is inter-
nally configured for -20 (see Figure 4).
The error amplifier may also be used to regulate the out-
put of the tertiary winding for implementing a primary-
side regulated isolated power supply (see Figure 7).
Calculate the output voltage using the following equation:
where N
the number of tertiary winding turns.
100Ω
C
3
0.47µF
IN
✕
M1
N
14
P
REF
S
R
100mΩ
SENSE
is the number of secondary turns and N
N
= 2.4V.
5
S
V
20Ω
SBL204OCT
1nF
OUT
V
OUT
=
C
IN
(OPTIONAL)
FB
=
N
N
, where R
S
T
⎛
⎜
⎝
1
+
⎛
⎜
⎝
4.7µH
1
L1
R
R
+
1
2
R
R
⎞
⎟ ×
⎠
1
2
IN
⎞
⎟ ×
⎠
V
REF
≅ 50kΩ is the input
R
2kΩ
R
2kΩ
1
2
V
REF
C
3
560µF
5V/10A
OUT
✕
V
OUT
0.1µF
T
is