FAN7554DTF Fairchild Semiconductor, FAN7554DTF Datasheet - Page 11

• Manufacturer Part Number: FAN7554DTF
• Description: IC CTRLR PWM CURRENT MODE 8SOIC
• Manufacturer: Fairchild Semiconductor

Specifications of FAN7554DTF

• Pwm Type: Current Mode
• Number Of Outputs: 1
• Frequency - Max: 500kHz
• Duty Cycle: 98%
• Voltage - Supply: 9 V ~ 30 V
• Buck: No
• Boost: No
• Flyback: Yes
• Inverting: No
• Doubler: No
• Divider: No
• Cuk: No
• Isolated: Yes
• Operating Temperature: -25°C ~ 85°C
• Package / Case: 8-SOIC (3.9mm Width)
• Frequency-max: 500kHz
• Output Current: 1 A
• Switching Frequency: 500 KHz
• Mounting Style: SMD/SMT
• Maximum Operating Temperature: + 85 C
• Minimum Operating Temperature: - 25 C
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: FAN7554DTFTR; FAN7554DTF_NL; FAN7554DTF_NLTR; FAN7554DTF_NLTR

Gate Driver
The gate drive circuit has the totem-pole output configuration. The output has 1A peak current and 200mA average current
drive ability.
ON/OFF Control
The FAN7554 is able to use the feedback pin for ON/OFF control by placing NPN transistor between the cathode of the
KA431 and ground as shown in figure 19. When the transistor turns on, the current flows through the photo diode and
saturates the photo transistor. As a result, the feedback voltage is dropped to zero. When the feedback voltage is below 0.3V,
the soft start voltage starts to discharge by connecting the internal resistor 1k in parallel with the external capacitor Cs. When
the soft start voltage becomes less than 1.5V, all the blocks in the FAN7554 are turned off , with the exceptions of the UVLO
block and ON/OFF control block. The operation current is about 200uA. So the stand-by power is reduced and SMPS
efficiency is improved. When the feedback voltage exceeds 0.3V, the FAN7554 normally operates by turning on Vref block.
6V
6V
3V
3V
Vfb
Vfb
t1
t1
Slope (dv/dt) = 5uA / Cfb
Slope (dv/dt) = 5uA / Cfb
Shutdown
Shutdown
Shutdown
Clock
Clock
Clock
Q
Q
Q
Figure 17-B . Delayed Shutdown & Feedback Waveform
Figure 18. Gate Drive Circuit
FAN7554
FAN7554
FAN7554
7
7
7
t2
t2
6
6
6
OUT
OUT
OUT
Shutdown start point
Shutdown start point
DRAIN
DRAIN
FAN7554
t
t
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