an8011s Panasonic Corporation of North America, an8011s Datasheet - Page 11

• Manufacturer Part Number: an8011s
• Description: 2-channel Step-down, Step-up, Or Inverting Use Dc-dc Converter Control Ic
• Manufacturer: Panasonic Corporation of North America

Voltage Regulators
[2] Function descriptions (continued)
[3] The time constant setting method for timer latch type short-circuit protection circuit
4. Timer latch short-circuit protection circuit
5. Low input voltage malfunction prevention circuit (U.V.L.O.)
6. PWM comparator block
7. Output block
8. Remote circuit
compares the output voltage of error amplifier V
conditions of DC-DC converter output is stabilized, there is no fluctuation of error amplifier output, and the short-
circuit protection comparator also keeps the balance. At this moment, the switch SW1 will be in the off state, and the
latch terminal voltage will be kept at approximately 0.9 V typical.
error amplifier to the noninverted input of the short-circuit protection comparator, the short-circuit protection com-
parator outputs the high-level signal. This signal turns on the switch SW1, and the charging to the capacitor C
connected externally to the latch terminal is started with a current of 80 A typical.
voltage lock-out circuit (U.V.L.O.) is enabled, thereby the ouput drive transistor is cut off and the dead-time is set to
100%.
supply is switched off.
Application Notes (continued)
destruction or deterioration if overload or short-circuit of power supply output lasts for a certain time.
the ouput level of either one or both of the error amplifiers exceeds 1.85 V typical, the timer circuit is actuated, and
initiates charging the external capacitor for protection enable.
this capacitor reaches 1.25 V, it sets the latch circuit, cuts off the ouput drive transistor, and sets the dead time to
100%.
supply voltage reduction in the transient state of power on or off.
supply voltage level, and cuts off the output drive transistor by resetting the latch circuit, thereby setting the dead-
time to 100% and keeping the latch terminal low.
of output pulse in accordance with the input voltage. It turns on the output transistor during the period when the
triangular wave of C
capacitor in parallel with the external resistor R
of the ouput pulse by the RC time constant when the power supply is turned on starts to work.
GND. The breakdown voltage of the collector ouput terminal is 34 V and it is possible to obtain up to 100 mA
ouput current.
lowered to a value below approximately 0.8 V, the internal reference voltage goes down, thereby the IC control
is stopped and the circuit current is decreased to 5 A or less. When the on/off terminal voltage is increased to a
value higher than approximately 2.0 V, the internal reference voltage raises and the control operation is started.
Figure 3 shows the block diagram of the protection latch circuit. The comparator for short-circuit protection
When the load conditions suddenly change, and high-level signal (1.85 V typical of higher) is inputted from the
When the external capacitor C
Once the under-voltage lock-out circuit (U.V.L.O.) is enabled, the latch circuit will not be reset unless the power
This circuit protects the external main swiching devices, switching diodes, choke coils, and etc. from
The timer latch type short-circuit protection circuit detects the output level of each error amplifier, and when
If the ouput of the error amplifier does not return to a normal voltage range by the time when the voltage of
This circuit protects the system from destruction or deterioration due to control malfunction caused by the
The low input voltage malfunction prevention circuit detects the internal reference voltage according to the
The PWM comparators, each has one inverted input, and two noninverted inputs, and controls the on-period
The dead-time is set by the addition of a resistor between the DTC terminal and GND. By the addition of a
The ouput drive transistor is of open-collector type output connected in Darlington circuit of emitter common
It is possible to switch on/off the IC control by an external control signal. When the on/off terminal voltage is
T
terminal is lower than either the error amplifier ouput voltage or the DTC terminal voltage.
S
is charged up to approximately 1.25 V typical, the latch circuit is set and the under-
FB
with the reference voltage (1.85 V) at all the time. When the load
DTC
, the soft start function which gradually extends the on-period
AN8011S
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