BD7682FJ-LB Datasheet, PDF (14/30 Pages) Rohm – This is the product guarantees long time support in the Industrial market

BD768xFJ-LB Series
Datasheet
(5) Soft Start Operations
Normally, a large current starts flowing to the AC/DC power supply when the AC power supply is turned ON.
BD768xFJ includes a soft start function to prevent large changes in the output voltage and output current during
startup.
This function is reset when the VCC pin voltage is at V_UVLO2 (7.5V typ) or below, or when the BO pin is at the B.O.
detection voltage (1.00V typ) or below (that is, when the AC power supply is unplugged), and soft start is
performed again at the next AC power-ON.
During a soft start, the following post-startup operations are performed. ( See turn OFF described above in section
4 (a)).
・Start to 1ms => Set to 25% of normal CS limiter value
・ 1ms to 4ms => Set to 50% of normal CS limiter value
・ > 4 ms… => Normal operation
(6) Over Load Protection Function
The overload protection function monitors the overload status of the secondary output current at the FB pin, and
fixes the OUT pin at low level when overload status is detected.
During overload status, current no longer flows to the photo-coupler, so the FB pin voltage rises.
When this status continues for the T_FOLP time (128ms typ), it is considered an overload and the OUT pin is fixed at
low level.
Once the FB pin voltage exceeds V_FOLP1 (2.8V typ), if it drops to lower than V_FOLP2 (2.6V typ) within the T_FOLP time
(128ms typ), the overload protection timer is reset.
At startup, the FB voltage is pulled up to the internal voltage by a pull-up resistor and operation starts once the
voltage reaches V_FOLP1 (2.8V typ) or above. Therefore, the design must be set the FB voltage at V_FOLP2 (2.6V typ)
or below within the t_FOLP (128ms typ) time.
In other words, the secondary output voltage start time must be set to within T_FOLP (128ms typ) after IC startup.
To release latching after selecting latch mode, first unplug the power supply, and then set V_CC< V_LATCH (typ= V_UVLO2
-3.5V)
(7) ZT Pin OVP (Over Voltage Protection)
ZT OVP (Over Voltage Protection) function is built in for ZT pin.
When the ZT pin voltage reaches V_ZTL (typ = 3.5V), overvoltage status is detected. ZT pin OVP protection is
performed in latch mode.
A mask time defined as T_LATCH (typ = 150µs) is built in for the ZT pin OVP function. When ZT OVP status continues
within 150 µs, overvoltage is detected. This function masks any surges (etc.) that occur at the pin. See the
illustration in Figure 12.
(A similar T_LATCH (typ = 150µs) is VCCOVP)
∆t₁ <t_LATCH (typ=150µs)
∆t₂ <t_LATCH (typ=150µs)
∆t₁
∆t₂
V_ZTL
(TYP=5.0V)
Figure 12. ZTOVP and Latch Mask Function
A: DC/DC pulse operation, ZT pin also has pulse operation
B: ZT pin voltage > V_ZTL (typ = 3.5V)
C: ZT pin voltage > V_ZTL (typ = 3.5V) status is within t_LATCH (typ = 150µs) period, so DC/DC normal operations are
reset
D: ZT pin voltage > V_ZTL (typ = 3.5V)
E: ZT pin voltage > V_ZTL (typ = 3.5V) status continues for t_LATCH (typ = 150µs), so latching occurs and DC/DC OFF
is set
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TSZ22111・15・001
14/27
TSZ02201-0F1F0A200050-1-2
17.Apr.2015. Rev.001