Rainbow Electronics MAX5095A - Manual (Page 16)

MAX5094A/B/C/D/MAX5095A/B/C
Advance Clock Output (ADV_CLK) (MAX5095C)
ADV_CLK is an advanced pulse output provided to
facilitate the easy implementation of secondary-side
synchronous rectification using the MAX5095C. The
ADV_CLK pulse width is 85ns (typically) with its rising
edge leading the rising edge of OUT by 110ns. Use
this leading pulse to turn off the secondary-side syn-
chronous-rectifier MOSFET (QS) before the voltage
appears on the secondary (see Figure 8). Turning off
the secondary-side synchronous MOSFET earlier
avoids the shorting of the secondary in the forward
converter. The ADV_CLK pulse can be propagated to
the secondary side using a pulse transformer or high-
speed optocoupler. The 85ns pulse, with 3V drive volt-
age (10mA source), significantly reduces the
volt-second requirement of the pulse transformer and
the advanced pulse alleviates the need for a high-
speed optocoupler.
High-Performance, Single-Ended, Current-Mode
PWM Controllers
16 ______________________________________________________________________________________
t ADV_CLK = 110ns
t
PULSE
= 85ns
OUT
ADV_CLK
R T /C T
Figure 4. ADV_CLK
Typical Application Circuits
R
T
R1
R2
1
2
4
3
REF
V
CC
GND
OUT
COMP
FB
R
T
/C
T
CS
8
7
5
6
MAX5094_
C
T
R ST
V
IN
C ST
V OUT
N
R CS
Figure 5. MAX5094_ Typical Application Circuit (Isolated Flyback with Primary-Side Regulation)