Fairchild Smart LED Lamp Driver IC with PFC Function Data Manual (1)
Summary
This smart LED lamp driver IC is a high-efficiency PWM controller designed for sophisticated buck converters requiring PFC function. It automatically handles both AC and DC input sources while providing advanced features like soft-start protection and UVLO for reliable operation. This guide details every aspect of the FL7701, including its complex operating modes, internal phase tracking, output frequency programming, and critical PCB layout guidelines. Ideal for electrical engineers developing next-generation LED lighting fixtures that demand high power factor correction in varied environments.
Page 1 Text Content
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AN-9744 Smart LED Lamp Driver IC with PFC Function Introduction The FL7701 is a PWM peak current controller for a buck The internal DAC_OUT reference signal is dependent on converter topology operating in Continuous Conduction the VCC voltage. Using the DAC_OUT signal and internal
Mode (CCM) with an intelligent PFC function using a clock, CLK_GEN; the FL7701 automatically makes a digital control algorithm. The FL7701 has an internal self- digital reference signal, DAC_OUT. If the FL7701 cannot biasing circuit that is a current source using a high-voltage detect the ZCD_OUT signal, the IC has an abnormal switching device. When the input voltage is applied to the internal reference signal. In this situation, this phenomenon HV pin is over 25V to 450V, the FL7701 maintains a causes a lighting flicker.
15.5VDC at the VCC pin. The FL7701 also has a UVLO block for stable operation. When the VCC voltage reaches higher than VCCST+, the UVLO block starts operation.hen the VCC drops below the VCCST-, IC operation stops. Hysteresis is provided for stable operation of the IC when input the voltage is in noisy circumstances or unstable conditions. The FL7701 has a “smart” internal block for AC input condition. If an AC source with 50Hz or 60Hz is applied, the IC automatically changes the internal reference to adjust to input conditions with an internal fixed transient time. When a DC source connects to the IC, the internal reference immediately changes to DC waveform.
Iline
LED Load
Figure 2. FL7701 Operation
FL7701 Soft-Start Function
VSUP_SEN HV HVVCC
Device The FL7701 has an internal soft-start to reduce inrush current at IC startup. When the IC starts operation, the
DSG DSG: Digital Sine-Wave Generator ZCD_OUT HV Device : High-Voltage Device
internal reference of the IC slowly increases up to a fixed
DAC_OUT
Driver level for around seven cycles. After settling down this OUT
transient period, the internal reference is fixed at a certain
Reference
DC level. In this time, the IC continually tries to find input
phase information from the VCC pin. If the IC succeeds in
getting phase information from the VCC, the IC automatically follows a similar shape reference, which it
Figure 1. Basic Block of FL7701
made during the transient times, seven periods. If not, the IC has a DC reference level.
© 2011 Fairchild Semiconductor Corporation www.fairchildsemi.com Rev. 1.0.0 • 10/11/11
Page Summary Contents For Fairchild Smart LED Lamp Driver IC with PFC Function Data Manual (1)
Manual Details
| Brand | Fairchild |
|---|---|
| Pages | 9 |
| File Size | 1.05 MB |
| Published | July 06, 2026 |
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Frequently Asked Questions
How do I ensure stable operation in noisy input conditions?
Add a small capacitor with values below 100pF to both the RT and ADIM pins for increased system reliability.
Can this IC operate using both AC and DC power sources?
Yes, the internal block automatically senses the input condition, adjusting its reference signal whether it detects 50Hz/60Hz AC or a DC waveform.
Is the ZCD pin required for startup?
The FL7701 cannot start operating if the Zero Crossing Detection (ZCD_OUT) signal is not connected to the chip.