ncp1593 ON Semiconductor, ncp1593 Datasheet - Page 6

• Manufacturer Part Number: ncp1593
• Description: 1 Mhz, 3 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 the high side FET
exceeds the overcurrent threshold limit for seven
consecutive switching cycles, overcurrent protection is
triggered.
engages. First, hiccup mode, turns off both FETs and
discharges the internal compensation network at the output
of the OTA. Next, the IC waits typically 4 x t
resets the overcurrent counter. After this reset, the circuit
attempts another normal soft−start. Hiccup mode reduces
input supply current and power dissipation during a short
circuit. It also allows for much improved system up−time,
allowing auto−restart upon removal of a temporary
short−circuit.
The under voltage lockout feature prevents the controller
NCP1593 detects high side switch current and then
Once the overcurrent protection occurs, hiccup mode
SS
ms and then
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PROTECTIONS
6
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. NCP1593 supports pre−bias
start up by holding Low side FETs off till soft start ramp
reaches the FB Pin voltage.
Power Good
pull−up resistor. It is actively held low in soft−start, standby,
and shutdown. PG releases when the FB voltage and thus the
output voltage rises above 90% of nominal regulation point.
The PG goes low when the FB voltage falls below 85% of
the regulation point.
Thermal Shutdown
internal thermal monitoring circuit. If the junction
temperature exceeds the thermal shutdown threshold both
the upper and lower MOSFETs will be shut OFF.
In some applications the controller will be required to start
Power Good (PG) is an open-drain output that requires a
The NCP1593 protects itself from over heating with an