MAX5941 Maxim, MAX5941 Datasheet - Page 17

• Manufacturer Part Number: MAX5941
• Description: IEEE 802.3af-Compliant Power-Over-Ethernet Interface/PWM Controller for Power Devices
• Manufacturer: Maxim

Figure 6. Flyback Converter
An internal 275kHz oscillator determines the switching
frequency of the controller. At the beginning of each
cycle, NDRV switches the N-channel MOSFET on.
NDRV switches the external MOSFET off after the maxi-
mum duty cycle has been reached, regardless of the
feedback.
The MAX5941B uses an internal ramp generator for
slope compensation. The internal ramp signal is reset
at the beginning of each cycle and slews at 26mV/µs.
The PWM comparator uses the instantaneous current,
the error voltage, the internal reference, and the slope
PWM Comparator and Slope Compensation
IEEE 802.3af-Compliant Power-Over-Ethernet
Interface/PWM Controller for Power Devices
25.5kΩ
R
DISC
______________________________________________________________________________________
R
CL
C
C
V
DD
IN
SS
V
UVLO
RCL
GATE
PGOOD
SS_SHDN
PGOOD
V
DD
EE
MAX5941A
GND
V+
NDRV
OPTO
OUT
V
CS
CC
V-
compensation (MAX5941A only) to determine when to
switch the N-channel MOSFET off. In normal operation,
the N-channel MOSFET turns off when:
where I
MOSFET, V
V
at 26mV/µs (MAX5941A only). When using the
MAX5941A in a forward-converter configuration, the fol-
lowing condition must be met to avoid control-loop sub-
harmonic oscillations:
SCOMP
100Ω
N
I
C
PRIMARY
T
M1
IN
PRIMARY
is a ramp function starting at zero and slewing
N
P
OPTOCOUPLER
REF
250VAC
4.7nF
R
×
C
SENSE
CC
R
N
is the current through the N-channel
is the 2.4V internal reference, and
SENSE
S
C
OUT
TLV431
>
V
OPTO
220Ω
- V
V
REF
OUT
R
R
1
2
- V
SCOMP
17