Datasheet

 2014 Microchip Technology Inc. DS20005308B-page 13
MCP16331
FIGURE 4-1: MCP16331 Block Diagram.
4.2 Functional Description
4.2.1 STEP-DOWN OR BUCK
CONVERTER
The MCP16331 is a non-synchronous, step-down or
buck converter capable of stepping input voltages
ranging from 4.4V to 50V down to 2.0V to 24V for
V
IN
> V
OUT
.
The integrated high side switch is used to chop or
modulate the input voltage using a controlled duty cycle
for output voltage regulation. High efficiency is
achieved by using a low-resistance switch, low forward
drop diode, low equivalent series resistance, inductor
and capacitor. When the switch is turned on, a DC
voltage is applied across the inductor (V
IN
- V
OUT
),
resulting in a positive linear ramp of inductor current.
When the switch turns off, the applied inductor voltage
is equal to -V
OUT
, resulting in a negative linear ramp of
inductor current (ignoring the forward drop of the
Schottky diode).
For steady-state, continuous inductor current
operation, the positive inductor current ramp must
equal the negative current ramp in magnitude. While
operating in steady state, the switch duty cycle must be
equal to the relationship of V
OUT
/V
IN
for constant
output voltage regulation, under the condition that the
inductor current is continuous, or never reaches zero.
For discontinuous inductor current operation, the
steady-state duty cycle will be less than V
OUT
/V
IN
to
maintain voltage regulation. The average of the
chopped input voltage or SW node voltage is equal to
the output voltage, while the average of the inductor
current is equal to the output current.
Schottky
Diode
C
OUT
C
BOOST
Slope
Comp
PWM
Latch
+
-
Overtemp
Precharge
R
Comp
Amp
+
-
C
COMP
R
COMP
HS
Drive
CS
V
REG
BG
REF
SS
V
REF
OVERTEMP
Boost
Pre
Charge
500 kHz OSC
S
V
OUT
V
OUT
R
SENSE
GND
Boost Diode
V
IN
EN
R
TOP
R
BOT
BOOST
SW
GND
FB
V
REF
SHDN all blocks
+
-
C
IN
+
+
L
Note: EN has an internal pull up, so the device will start even if the EN pin is left floating.