Microchip Technology ADM00423 Data Sheet

© 2011 Microchip Technology Inc.

DS22285A-page 15

The MCP16321/2 is a high-input voltage, step-down
regulator, capable of supplying 1A/2A to a regulated
output voltage from 0.9V to 5V. Internally, the 1 MHz
oscillator provides a fixed frequency, while the Peak
Current Mode Control architecture varies the duty cycle
for output voltage regulation. An internal floating driver
is used to turn the high-side integrated N-Channel
MOSFET on and off. The power for this driver is
derived from an external boost capacitor whose energy
is replenished when the low-side N-Channel MOSFET
is turned on. When the maximum duty cycle
approaches 100%, the boost capacitor is replenished
for 240 ns after every 8 cycles.

4.1.1

INTERNAL REFERENCE VOLTAGE 
V

REF

 

For the adjustable version, an integrated precise 0.9V
reference combined with an external resistor divider
sets the desired converter output voltage. The resistor
divider can vary without affecting the control system
gain. High-value resistors consume less current, but
are more susceptible to noise. For the fixed version, an
integrated precise voltage reference is set to the
desired V

OUT

 value and is directly connected to V

OUT

.

4.1.2

INTERNAL COMPENSATION

All control system components necessary for stable
operation over the entire device operating range are
integrated, including the error amplifier and inductor
current slope compensation.

4.1.3

EXTERNAL COMPONENTS

External components consist of:
• Input capacitor
• Output filter (inductor and capacitor)
• Boost capacitor
• Resistor divider (adjustable version only)
The selection of the external inductor, output capacitor,
input capacitor and boost capacitor is dependent upon
the output voltage and the maximum output current.

4.1.4

ENABLE INPUT

The enable input (EN) is used to disable the device. If
disabled, the device consumes a minimal current from
the input. Once enabled, the internal soft start controls
the output voltage rate of rise, preventing high-inrush
current and output voltage overshoot. The EN is
internally pulled up or enabled; to disable the converter,
it must be pulled low.

4.1.5

SOFT START

The internal reference voltage rate of rise is controlled
during startup, minimizing the output voltage overshoot
and the inrush current.

4.1.6

OUTPUT OVER VOLTAGE 
PROTECTION

If the output of the regulator exceeds 103% of the
regulation voltage, the SW outputs will tri-state to
protect the device from damage. This check occurs at
the start of each switching cycle.

4.1.7

INPUT UNDER VOLTAGE LOCKOUT

An integrated Under Voltage Lockout (UVLO) prevents
the converter from starting until the input voltage is high
enough for normal operation. The converter will
typically start at 5.75V (typical) and operate down to
5.25V (typical). Hysteresis of 500 mV (typical) is added
to prevent starting and stopping during startup, as a
result of loading the input voltage source.

4.1.8

MINIMUM DUTY CYCLE

A minimum duty cycle of 70 ns typical prevents the
device from constant switching for high step-down
voltage ratios. Duty cycles less than this minimum will
initiate pulse skipping to maintain output voltage
regulation, resulting in higher output voltage ripple.
Duty cycle for continuous inductor current operation is
approximated by V

OUT

/V

IN

. For a 1 MHz switching

frequency or 1 µs period, this results in a 7% duty cycle
minimum. Maximum V

IN

 for continuous switching can

be approximated dividing V

OUT

 by the minimum duty

cycle or 7%. For example, the maximum input voltage
for continuous switching for a 1.5V output is equal to
approximately 21V.