MAX5071 Maxim Integrated Products, MAX5071 Datasheet - Page 16

• Manufacturer Part Number: MAX5071
• Description: (MAX5070 / MAX5071) Current-Mode PWM Controllers
• Manufacturer: Maxim Integrated Products

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High-Performance, Single-Ended, Current-Mode
PWM Controllers
Figure 4. ADV_CLK
Figure 5. MAX5070A/MAX5070B Typical Application Circuit (Isolated Flyback with Primary-Side Regulation)
16
ADV_CLK
______________________________________________________________________________________
R
T
OUT
/C
T
V
R1
R2
IN
C
R
T
T
t
t
PULSE
ADV_CLK
1
2
3
4
COMP
FB
CS
R
= 85ns
T
/C
= 110ns
T
MAX5070A
MAX5070B
VREF
GND
OUT
V
CC
8
7
6
5
ADV_CLK is an advanced pulse output provided to
facilitate the easy implementation of secondary-side
synchronous rectification using the MAX5071C. 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.
When the MAX5070/MAX5071s’ die temperature goes
above +150°C, the thermal-shutdown circuitry will shut
down the 5V reference and pull OUT low.
C
ST
R
ST
Advance Clock Output (ADV_CLK) (MAX5071C)
Typical Application Circuits
N
R
CS
Thermal Shutdown
V
OUT