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NCP1512 Datasheet(PDF) 6 Page - ON Semiconductor

Part No. NCP1512
Description  PWM Buck Converter
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Maker  ONSEMI [ON Semiconductor]
Homepage  http://www.onsemi.com
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NCP1512 Datasheet(HTML) 6 Page - ON Semiconductor

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NCP1512
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6
INTRODUCTION
The NCP1512 is a tri-mode regulator intended for use in
baseband supplies for portable equipment. Its unique
features provide an efficient power supply for a portable
device at full operating current, while also providing
extremely low standby current for idle mode operation.
When the system is idle, the user can activate the pulsed
mode function. In this mode, the regulator provides a
regulated low current output voltage keeping the system
biased. When the device is in its normal operating mode,
the regulator synchronizes to the system clock or uses an
internal 1.0 MHz clock and turns into a switching regulator.
This allows the regulator to provide efficient power to the
system. This circuit is patent pending.
Operation Description
The Buck regulator is a synchronous rectifier PWM
regulator with integrated MOSFETs. This regulator has a
Pulsed function for low power modes to conserve power.
The Tri PWM with external or internal oscillator/pulsed
mode is an exclusive Patent Pending circuit.
For the PWM Synchronization mode, the operating
frequency range for the NCP1512 is 450 to 1000 kHz. The
output current of the PWM is optimized for 100 mA with
a maximum current supply in excess of 300 mA for the 2.5
to 5.2 input voltage range.
If the Sync Pin is held low, the NCP1512 changes into the
Pulsed mode. The Pulsed function assures the user of an
extremely low input current and greatly reduced quiescent
current when the users system is in a sleep mode. Internally
to the NCP1512, the Synchronization pin has a pull down
resistor to force the part into Pulsed mode when a clock
signal is not present. The Pulsed mode supplies a current in
excess of 30 mA.
If the Sync Pin is held high, NCP1512 enters a PWM
mode with an internal 1.0 MHz oscillator. The PWM mode
has the same operational characteristics (current limit,
maximum output current, etc.) as the synchronized PWM
mode. The Sync Pin threshold is fixed as noted in the
Electrical Characteristics table.
Table 1. Sync Pin Input with Corresponding
Operational Mode of NCP1512
Sync Pin State
Operational Mode
Low
Low Iq Pulsed Mode Operation
High
PWM Using Internal Oscillator for the Clock
Clock
PWM Using Rising Edge of Clock Signal to
Turn On PFET Pass Element
PWM Mode with External Synchronization Signal
During normal operation, a synchronization pulse acts as
the clock for the DC/DC controller. The rising edge of the
clock pulls the gate of Q1 low allowing the inductor to
charge. When the current through Q1 reaches either the
current limit or feedback voltage reaches its limit, Q1 will
turn off and Q2 will turn on. Q2 replaces the free wheeling
diode typically associated with Buck Converters. Q2 will
turn off when either a rising edge sync pulse is present or
all the stored energy is depleted from the inductor.
The output voltage accuracy in the PWM mode is well
within 3% of the nominal set value. An overvoltage
protection circuit is present in the PWM mode to limit the
positive voltage spike due to fast load transient conditions.
If the OVP comparator is activated, the duty cycle will be
0% until the output voltage falls to the nominal level. The
PWM also has the ability to go to 100% duty cycle for
transient conditions and low input to output voltage
differentials.
The PWM mode operates as a forced-PWM converter.
Each switching cycle has a typical on-time of 75 nsec.
NCP1512 has two protection circuits that can eliminate the
minimum on time for the cycle. When tripped, the
overvoltage protection or the thermal shutdown overrides
the gate drive of the high side MOSFET.


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