FAN7631 Fairchild Semiconductor, FAN7631 Datasheet - Page 14

• Manufacturer Part Number: FAN7631
• Description: The FAN7631 is a pulse-frequency modulation controller for high-efficiency half-bridge resonant converters that includes a high-side gate drive circuit, an accurate current-controlled oscillator, and various protection functions
• Manufacturer: Fairchild Semiconductor

© 2011 Fairchild Semiconductor Corporation
FAN7631 • 1.0.2
5.5. Over-Voltage Protection (OVP)
When the LV
protection is used when auxiliary winding of the
transformer is utilized to supply V
5.6. Thermal Shutdown (TSD)
The thermal shutdown function is integrated to detect
abnormal over-temperature, such as abnormal ambient
temperature rising or over-driving of gate drive circuit. If
the junction temperature exceeds T
shutdown is triggered in Latch Mode.
5.7. Line-UVLO
FAN7631 includes a precise line-UVLO (or brownout)
function with programmable hysteresis voltage, as can
be seen in Figure 39. When the line voltage is recovered,
it starts up with soft-start, as shown in Figure 39. A
hysteresis voltage between the start and stop voltage is
programmable by I
operation, the comparator’s output is HIGH and I
disabled I
is LOW, introducing hysteresis.
If necessary, C
interference. Generally, hundreds of pico-farad to tens of
nano-farad is adequate depending on the level of noise.
The DC link input-voltages for start and stop are
calculated as:
V
V
DL START
DL STOP
,
,
LINE
Figure 40.


is activated when the comparator’s output
CC
V
V
LINE
DL STOP
Figure 39.
Filter
reaches 23V, OVP is triggered. This
,
LINE

R
and external resistor R1. In normal
can be used to reduce noise

1
Line UVLO Waveforms
R

I
2
LINE
R
2

Line-UVLO
R
1
CC
to the FAN7631.
SD
(130C), thermal
LINE
(8)
is
14
6. Simple Remote-On/Off
The power stage can be shut down with Latch Mode or
Auto-Restart Mode, as shown in Figure 41. For the Latch
Mode protection, the FI pin is used, which stops the
switching immediately once the voltage on FI pin is
pulled above V
an external protection with Auto-Restart Mode, an opto-
coupler can be used on the LS pin. When voltage on the
LS pin is pulled below V
When LS pin voltage is pulled HIGH, above 3V,
FAN7631 starts up softly.
7. Skip Cycle Operation
The FAN7631 provides the pulse-skip function to prevent
the switching frequency from increasing too much at no-
load condition. Figure 42 shows the internal block
diagram for the control (CON) pin and its external
configuration. The CON pin is typically connected to the
collector terminal of the opto-coupler and the FAN7631
stops switching when the CON pin voltage drops below
0.4V. FAN7631 resumes switching when the CON pin
voltage rises above 0.6V. The frequency that causes
pulse skipping is given as:
f
SKIP
Figure 41.

Figure 42.
(
(Top: Latch Mode, Bottom: A/R Mode)
5.8
R
FI
min
k
(4V) using an opto-coupler. To configure


External Protection Circuits
4.6
R
Pulse-Skipping Circuit
LINE
max
k

(3V), line UVLO is triggered.
) 100

kHz
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