Datasheet

MAX5941A/MAX5941B
IEEE 802.3af-Compliant Power-Over-Ethernet
Interface/PWM Controller for Power Devices
16 ______________________________________________________________________________________
to 2.4V, the internal voltage reference. Pull V
SS_SHDN
below 0.25V to disable the controller.
Undervoltage lockout shuts down the controller when
V
CC
is less than 6.6V. The regulators for V+ and the ref-
erence remain on during shutdown.
Current-Sense Comparator
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
SENSE
, according to the following equation:
where I
LimPrimary
is the maximum peak primary-side
current.
When V
CS
> 465mV, the power MOSFET switches off.
The propagation delay from the time the switch current
reaches the trip level to the driver turn-off time is 170ns.
RI
SENSE LimPrimary
= 0 465./V
MAX5941B
V
DD
UVLO
RCL
V+GND
SS_SHDN
PGOOD
PGOOD
GATE
V
EE
NDRV
CS
V-
V
CC
OPTO
V
IN
(30V TO 72V)
V
OUT
OPTOCOUPLER
C
DD
47µF
C
SS
0.1µF
R
DISC
25.5kΩ
3kΩ
4.75kΩ
C
CC
10µF
100Ω
R
SENSE
100mΩ
20Ω
R
1
25.5kΩ
R
2
8.25kΩ
C
OUT
3 × 560µF
0.1µF
C
IN
3 × 0.47µF
L1
4.7µH
0.1µF
240kΩ
N
T
N
R
N
P
N
S
M1
IRF640N
4.7nF
250VAC
TLV431
1N4148
6
CMHD2003
14
5
1nF
SBL204OCT
5V/10A
220Ω
14
R
CL
OUT
Figure 5. Forward Converter