ncp15889 ON Semiconductor, ncp15889 Datasheet - Page 7

• Manufacturer Part Number: ncp15889
• Description: Single Phase Buck Controller
• Manufacturer: ON Semiconductor

Overcurrent Protection (OCP)
the voltage at the LX, at the end of LG on time to an
internally generated fixed voltage. If the phase voltage is
lower than OCP trip voltage, an overcurrent condition
occurs and a counter is initiated.
PWM logic and both HS-FET and LS-FET are turned off.
Power has to be recycled to exit out of the overcurrent fault.
The minimum turn-on time of the LS-FET is set to be
500 ns.
Threshold ranging from 50 mV to 550 mV, simply by
adding a resistor (ROCSET) between LG and GND. During
a short period of time following V
threshold, an internal 10 mA current (IOCSET, trimmed to
$5%) is sourced from LG pin, determining a voltage drop
across ROCSET. This voltage drop will be sampled and
internally held by the device as OverCurrent Threshold. The
OC setting procedure overall time length is about 4.2 ms.
Connecting a ROCSET resistor between LG and GND, the
programmed threshold will be:
is not connected, the device switches the OCP threshold to
a fixed 640 mV value: an internal safety clamp on BG is
triggered as soon as LG voltage reaches 700 mV, enabling
the 640 mV fixed threshold and ending OC setting phase.
The current trip threshold tolerance is ±25 mV. The accuracy
of the set point is best at the highest set point. The accuracy
will decrease as the set point decreases.
The low-side R
When the counter completes after two clock cycles, the
NCP158x allows to easily program an Overcurrent
RSET values range from 5 kW to 55 kW. In case ROCSET
I
OCth
+
I
OCSET
DSon
R
DS(on)
@ R
sense is implemented by comparing
OCSET
CC
rising over UVLO
APPLICATIONS INFORMATION
NCP1588, NCP1589
http://onsemi.com
7
Internal Soft –Start
which reduces the inrush current and overshoot of the output
voltage. Figure 7. shows a typical soft-start sequence.
Soft-Start is achieved by ramping the internal reference
using the oscillator clock (64 steps from 0 V to 0.8 V of
V
OCP programming → Comp voltage reach the lower end of
the Ramp voltage (1.45 V). The typical soft-start time is
4.2 ms. The internal soft-start is held low when the part is
in UVLO or Disable mode.
Power Good
output can be pulled up high to the appropriate level with an
external resistor. It monitors the output voltage through the
VOS pin. The PGOOD is flagged low for ±10% of Vout for
OV/UV trip points respectively. The separate VOS input is
not slowed down by the compensation on the VFB pin. The
PGOOD output can deliver a max of 4 mA sink current at
0.4 V when de-asserted. The PGOOD pin is held low during
soft-start. Once soft-start is complete PGOOD goes high if
there are no faults without any delays associated to it.
Undervoltage Protection
device turns off both HS and LS MOSFETs, latching the
condition. This requires a POR to recover.
overvoltage protection turns off UG MOSFET and turns on
LG MOSFET. The LG MOSFET will be turned off as soon
as VOS goes below Vref/2 (0.4 V). The condition is latched,
and requires POR to recover. The device still controls the LG
MOSFET and can switch it on whenever VOS rises above
0.4 V.
Overvoltage Protection
ref
The NCP158x features an internal soft-start function,
Power Good is an open drain and active high output. This
If the voltage at VOS pin drops below UV threshold, the
If the voltage at VOS pin rises over OV threshold (1V typ),
). The order of startup sequence is as follows: UVLO →