ncp1589l ON Semiconductor, ncp1589l Datasheet - Page 6

• Manufacturer Part Number: ncp1589l
• Description: Ncp1589l Low Voltage Synchronous Buck Controller With Light Load Efficiency And Transient Enhancement
• Manufacturer: ON Semiconductor

Overcurrent Protection (OCP)
MOSFET and used this information to determine if there is
excessive output current. The voltage across the low side
MOSFET is measured from the LX pin when it is conducted,
and is referenced to ground. The overcurrent measurement
is timed to occur at the end of the low side MOSFET
conduction period.
the overcurrent protection threshold, then an internal
counter is triggered and incremented. If the voltage drop
does not exceed the threshold for the next cycle, the internal
counter will be reset. The NCP1589L will latch the over
current protection fault condition after 4 consecutive cycles
of overcurrent events.
fault, both the high side and low side MOSFETs are turned
off. To reset the overcurrent protection fault, the power to the
V
varying the R
to ground. During power on reset, after the V
pins both pass the undervoltage lockout threshold, the
NCP1589L will source a 10 mA current from LG pin through
the R
be sampled and locked by the device as the overcurrent
protection threshold. For example, if R
the 10 mA of current will yield a 100 mV threshold, and if
the voltage across the low side MOSFET exceeds 100 mV
at the end of the its conduction period, an overcurrent event
will be detected. The OCP threshold is only associated with
power on reset, and won’t be wiped out by pulling COMP
pin down (disabling the part).
protection threshold will max out at 640 mV. The
recommended range for R
yields a threshold voltage range of 50 mV to 600 mV.
Internal Soft−Start
NCP1589L uses a calibrated current source with an internal
soft−start capacitor to ramp the reference voltage from 0 V
to 800 mV over a period of around 4 ms. The soft−start ramp
generator will reset if the input power supply voltages reach
the undervoltage lockout threshold, or if the NCP1589L is
disabled by having the COMP pin pulled low.
Startup into a Precharged Load
charge on the output capacitors. Instead of fully discharging
the capacitors, the soft−start will begin from the precharged
output voltage level. For example, if the NCP1589L is
configured to provide a regulated output voltage of 2.5 V, the
normal soft−start sequence will ramp the output voltage
CC
The NCP1589L monitors the voltage across the low side
If the voltage drop across the bottom MOSFET exceeds
When the NCP1589L latches an overcurrent protection
The overcurrent threshold can be set externally, by
If the R
To prevent excess inrush current during startup, the
During a startup, the NCP1589L will detect the residual
pin must be cycled.
OCSET
OCSET
resistor and produce a voltage. This voltage will
OCSET
resistor is not present, the overcurrent
resistor shunted from low side gate pin
OCSET
is 5 kW to 60 kW which
OCSET
APPLICATIONS INFORMATION
CC
is set to 10 kW,
and BOOT
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6
from 0 to 2.5 V in 4.2 ms; however if the output capacitors
already has 1.2 V voltage, the NCP1589L will not discharge
the capacitors, instead the soft−start sequence will begin at
1.2 V and then ramp the output up to 2.5 V.
Power Good
active high output to signal the condition of the converter.
PGOOD is pulled low during soft−start cycle, and if there is
overvoltage or undervoltage fault. If the voltage on the FB
pin is within ±10% of V
will not be pulled low. The PGOOD pin does not have an
internal pull-up resistor.
Overvoltage Protection (OVP)
threshold (1000 mV, 125% of V
latch an overvoltage fault. During an overvoltage fault event
the UG pin will be pulled low, and the LG pin will stay high
until the voltage on the FB pin goes below V
If the overvoltage fault condition stays, the NCP1589L will
continue drive the LG pin, LG will go high if FB exceeds
1000 mV, then go low when FB is below 400 mV. The power
of the NCP1589L needs to be cycled up to clear the
overvoltage fault.
Undervoltage Protection (UVP)
threshold after the soft−start cycle completes, then the
NCP1589L will latch an undervoltage fault. During an
undervoltage fault, both the UG and LG pins will be pulled
low. Toggling power or COMP pin will reset the
undervoltage protection unit.
VORPM (RPM threshold)
frequency is controlled by COMP ripple voltage and RPM
threshold. The VORPM pin is connected to the output
voltage through an external divider. This voltage value is
proportional to the output voltage and sets the RPM
threshold voltage internally with input voltage information
obtained through the switch node. The internal RPM
threshold voltage (DTH) is a function of both V
VORPM pin V
the offset voltage of the threshold.
voltage, an internal ramp signal is started and UG is driven
high. When the internal ramp intercepts with COMP
voltage, the UG pin is reset low. The NCP1589L system
operates at pseudo-fixed frequency in continuous current
The PGOOD pin is an open drain connection, with an
If the voltage on the FB pin exceeds the overvoltage
The NCP1589L runs in RPM mode, its switching
Where R9/R10 (Figure 1) is the input voltage divider of
Each time when COMP voltage exceeds RPM threshold
If the voltage on the FB pin falls below the undervoltage
DTH +
ramp
V
out
is the internal ramp amplitude, V
V
in
R10)R9
ref
R9
(800 mV) then the PGOOD pin
V
ramp
ref
), the NCP1589L will
) V
offset
ref
/2 (400 mV).
out
and V
(eq. 1)
offset
in
is
.