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FAN7688 —Advanced Secondary Side LLC Resonant Converter Controller with Synchronous Rectifier Control
November 2015
FAN7688
Advanced Secondary Side LLC Resonant Converter
Controller with Synchronous Rectifier Control
Features
Secondary Side PFM Controller for LLC Resonant
Converter with Synchronous Rectifier Control
Charge Current Control for Better Transient
Response and Easy Feedback Loop Design
Adaptive Synchronous Rectification Control with
Dual Edge Tracking
Closed Loop Soft-Start for Monotonic Rising Output
Wide Operating Frequency (39 kHz ~ 690 kHz)
Green Functions to Improve Light-Load Efficiency
Description
The FAN7688 is an advanced Pulse Frequency
Modulated (PFM) controller for LLC resonant converters
with Synchronous Rectification (SR) that offers best in
class efficiency for isolated DC/DC converters. It
employs a current mode control technique based on a
charge control, where the triangular waveform from the
oscillator is combined with the integrated switch current
information to determine the switching frequency. This
provides a better control-to-output transfer function of
the power stage simplifying the feedback loop design
while allowing true input power limit capability. Closed-
loop soft-start prevents saturation of the error amplifier
and allows monotonic rising of the output voltage
regardless of load condition. A dual edge tracking
adaptive dead time control minimizes the body diode
conduction time thus maximizing efficiency.
-
Symmetric PWM Control at Light-Load to Limit
the Switching Frequency while Reducing
Switching Losses
-
Disabling SR at Light-Load Condition
Protection Functions with Auto-Restart
-
Over-Current Protection (OCP)
-
Output Short Protection (OSP)
-
NON Zero-Voltage Switching Prevention (NZS)
by Compensation Cutback (Frequency Shift)
Applications
Desktop ATX, Desktop-Derived Server, Blade
Server, and Telecom Power Supplies
Intelligent 100 W-2 kW+ Off-Line Power Supplies
High Efficiency Isolated DC-DC Converters
Large Screen Display Power
Industrial Power
-
Power Limit by Compensation Cutback
(Frequency Shift)
-
Overload Protection (OLP) with Programmable
Shutdown Delay Time
-
Over-Temperature Protection (OTP)
Programmable Dead Times for Primary Side
Switches and Secondary Side Synchronous
Rectifiers
V
DD
Under-Voltage Lockout (UVLO)
Wide Operating Temperature Range -40°C to
+125°C
Ordering Information
Part Number
FAN7688SJX
Note:
1.
All packages are lead free per JEDEC: J-STD-020B standard.
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