NCP6323, NCV6323
www.onsemi.com
9
DETAILED DESCRIPTION
General
The NCP/NCV6323 is a synchronous buck converter
which is optimized to supply different sub−systems of
portable applications powered by one cell Li−ion or three
cell Alkaline/NiCd/NiMH batteries. The devices are able to
deliver up to 2 A on an external adjustable voltage.
Operation with 3 MHz switching frequency allows
employing small size inductor and capacitors. Input supply
voltage feedforward control is employed to deal with wide
input voltage range. Synchronous rectification offer
improved system efficiency.
PWM Mode Operation
In medium and heavy load range, the inductor current is
continuous and the device operates in PWM mode with fixed
switching frequency, which has a typical value of 3 MHz. In
this mode, the output voltage is regulated by on−time pulse
width modulation of an internal P−MOSFET. An internal
N−MOSFET operates as synchronous rectifier and its
turn−on signal is complimentary to that of the P−MOSFET.
Undervoltage Lockout
The input voltage VIN must reach or exceed 2.5 V
(typical) before the NCP/NCV6323 enables the converter
output to begin the start up sequence. The UVLO threshold
hysteresis is typically 100 mV.
Enable
The NCP/NCV6323 has an enable logic input pin EN. A
high level (above 1.1 V) on this pin enables the device to
active mode. A low level (below 0.4 V) on this pin disables
the device and makes the device in shutdown mode. There
is an internal filter with 5 ms time constant. The EN pin is
pulled down by an internal 10 nA sink current source. In
most of applications, the EN signal can be programmed
independently to VIN power sequence.
Figure 19. Power Good and Active Discharge Timing Diagram
Power Good Output
The device monitors the output voltage and provides a
power good output signal at the PG pin. This pin is an
open−drain output pin. To indicate the output of the
converter is established, a power good signal is available.
The power good signal is low when EN is high but the output
voltage has not been established. Once the output voltage of
the converter drops out below 90% of its regulation during
operation, the power good signal is pulled low and indicates
a power failure. A 5% hysteresis is required on power good
comparator before signal going high again.
Soft−Start
A soft start limits inrush current when the converter is
enabled. After a minimum 300 ms delay time following the
enable signal, the output voltage starts to ramp up in 100 ms
(NCV6323) / 240 ms (NCP6323) (for external adjustable
voltage devices) or with a typical 10 V/ms slew rate (for
fixed voltage devices).
Active Output Discharge
An output discharge operation is active in when EN is low.
A discharge resistor (500 W typical) is enabled in this
condition to discharge the output capacitor through SW pin.
