ncp1597 ON Semiconductor, ncp1597 Datasheet - Page 6

• Manufacturer Part Number: ncp1597
• Description: 1 Mhz, 2.0 A Synchronous Buck Regulator
• Manufacturer: ON Semiconductor

Undervoltage Lockout (UVLO)
from switching when the input voltage is too low to power
the internal power supplies and reference. Hysteresis must
be incorporated in the UVLO comparator to prevent IxR
drops in the wiring or PCB traces from causing ON/OFF
cycling of the controller during heavy loading at power up
or power down.
Overcurrent Protection (OCP)
compares to a voltage level representing the overcurrent
threshold limit. If the current through high side FET exceeds
the overcurrent threshold limit, overcurrent protection is
triggered. The system ignores the overcurrent signal for the
leading edge blanking time at the beginning of each cycle to
avoid any turn−on noise glitches.
cycle after a propagation delay. This cycle−by−cycle current
limit circuit limits peak current to 3.0 A during overload and
short circuit conditions.
protection even during soft start period. A short circuit
counter accumulates 7 consecutive current limit signal then
triggers the hiccup mode. During hiccup mode, both FETs
The under voltage lockout feature prevents the controller
NCP1597/A detects high side switch current and then
Then the high side MOSFET is turned−off for the rest of
An extra short circuit protection circuit provides robust
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PROTECTIONS
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are turned off and soft−start capacitor and COMP Pin is
discharged. The hiccup time is 2 ms typical. After the hiccup
timer is up, the short circuit timer is reset. After reset, normal
soft start is attempted. This scheme reduces input supply
current and power dissipation during short circuit. It also
allows for much improved system up−time, allowing
auto−restart upon removal of a temporary short−circuit.
Pre−Bias Startup
switching when it’s output capacitors are charged anywhere
from slightly above 0 V to just below the regulation voltage.
This situation occurs for a number of reasons: the
converter’s output capacitors may have residual charge on
them or the converter’s output may be held up by a low
current standby power supply. NCP1597/A supports
pre−bias start up by holding Low side FETs off till soft start
ramp reaches the FB Pin voltage.
Thermal Shutdown
internal thermal monitoring circuit. If the junction
temperature exceeds the thermal shutdown threshold the
voltage at the COMP pin will be pulled to GND and both the
upper and lower MOSFETs will be shut OFF.
In some applications the controller will be required to start
The NCP1597/A protects itself from over heating with an