Datasheet

MCP16331
DS20005308B-page 12  2014 Microchip Technology Inc.
4.0 DETAILED DESCRIPTION
4.1 Device Overview
The MCP16331 is a high input voltage step-down
regulator, capable of supplying 500
mA to a regulated
output voltage from 2.0V to 24V. Internally, the trimmed
500 kHz 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
(C
BOOST
) whose energy is supplied from a fixed
voltage ranging between 3.0V and 5.5V, typically the
input or output voltage of the converter. For
applications with an output voltage outside of this
range, 12V for example, the boost capacitor bias can
be derived from the output using a simple Zener diode
regulator.
4.1.1 INTERNAL REFERENCE VOLTAGE
V
REF
An integrated precise 0.8V reference combined with an
external resistor divider sets the desired converter out
-
put voltage. The resistor divider range can vary without
affecting the control system gain. High-value resistors
consume less current, but are more susceptible to
noise.
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. To add the proper amount
of slope compensation, the inductor value changes
along with the output voltage (see
Table 5-1).
4.1.3 EXTERNAL COMPONENTS
External components consist of:
• input capacitor
• output filter (inductor and capacitor)
• freewheeling diode
• boost capacitor
• boost blocking diode
• resistor divider
The selection of the external inductor, output capacitor,
input capacitor and freewheeling diode is dependent
upon the output voltage, input voltage and the
maximum output current.
4.1.4 ENABLE INPUT
Enable input is used to disable the device, while
connected to GND. If disabled, the MCP16331 device
consumes a minimal current from the input.
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 UNDERVOLTAGE LOCKOUT
An integrated Undervoltage Lockout (UVLO) prevents
the converter from starting until the input voltage is high
enough for normal operation. The converter will typically
start at 4.1V and operate down to 3.6V. Hysteresis is
added to prevent starting and stopping during start-up
as a result of loading the input voltage source.
4.1.7 OVERTEMPERATURE
PROTECTION
Overtemperature protection limits the silicon die
temperature to +160°C by turning the converter off. The
normal switching resumes at +130°C.