FA531X series
The detection threshold is -0.17V for FA5314/15 with respect to
ground as shown in Figure 17.
The operation is similar to that of FA5310B/11B/16/17 except
the threshold is minus voltage compared to that which is plus
voltage for FA5310B/11B/16/17.
Figure 18 is a timing chart which illustrates current limiting
operations.
6. Undervoltage lockout circuit
The IC incorporates a circuit which prevents the IC from
malfunctioning when the supply voltage drops. When the
supply voltage is raised from 0V, the IC starts operation with
VCC=VCC ON.
If the supply voltage drops, the IC shuts its output down when
VCC=VCC OFF. When the undervoltage lockout circuit operates,
the CS pin goes low to reset the IC.
7. Output circuit
As shown in Figure 19, the IC's totem-pole output can directly
drive the MOSFET. The OUT pin can source and sink currents
of up to 1.5A or 1.0A.
Fig. 17 Overcurrent limiting circuit for FA5314/15
If IC operation stops when the undervoltage lockout circuit
operates, the gate voltage of the MOSFET goes low and the
MOSFET is shut down.
CS pin voltage (3.6V)
DT voltage
Oscillator output
FB pin voltage
H
OUT pin output
L
IS ( – ) pin voltage
Comparator C4
Minus
detection
Reference
voltage (– 0.17V)
Bias voltage
OFF
Overcurrent limiting
Fig. 18 Overcurrent timing chart for FA5314/15
Fig. 19 Output circuit
8
FUJI [ FUJI ELECTRIC ]
