MCP16301 MICROCHIP [Microchip Technology], MCP16301 Datasheet - Page 13

• Manufacturer Part Number: MCP16301
• Description: High Voltage Input Integrated Switch Step-Down Regulator
• Manufacturer: MICROCHIP [Microchip Technology]

4.2.2
The MCP16301 integrates a Peak Current Mode
Control architecture, resulting in superior AC regulation
while minimizing
compensation
integration. Peak Current Mode Control takes a small
portion of the inductor current, replicates it and
compares this replicated current sense signal with the
output of the integrated error voltage. In practice, the
inductor current and the internal switch current are
equal during the switch-on time. By adding this peak
current sense to the system control, the step-down
power train system is reduced from a 2
order. This reduces the system complexity and
increases its dynamic performance.
For Pulse-Width Modulation (PWM) duty cycles that
exceed 50%, the control system can become bimodal
where a wide pulse followed by a short pulse repeats
instead of the desired fixed pulse width. To prevent this
mode of operation, an internal compensating ramp is
summed into the current shown in
4.2.3
The internal oscillator periodically starts the switching
period, which in MCP16301’s case occurs every 2 µs
or 500 kHz. With the integrated switch turned on, the
inductor current ramps up until the sum of the current
sense and slope compensation ramp exceeds the inte-
grated error amplifier output. The error amplifier output
slews up or down to increase or decrease the inductor
peak current feeding into the output LC filter. If the reg-
ulated output voltage is lower than its target, the invert-
ing error amplifier output rises. This results in an
increase in the inductor current to correct for errors in
the output voltage. The fixed frequency duty cycle is
terminated when the sensed inductor peak current,
summed with the internal slope compensation,
exceeds the output voltage of the error amplifier. The
PWM latch is set by turning off the internal switch and
preventing it from turning on until the beginning of the
next cycle. An overtemperature signal, or boost cap
undervoltage, can also reset the PWM latch to asyn-
chronously terminate the cycle.
© 2011 Microchip Technology Inc.
PEAK CURRENT MODE CONTROL
PULSE-WIDTH MODULATION
(PWM)
components, and their
the
number
Figure
of
nd
voltage loop
order to a 1
4-1.
size, for
st
4.2.4
The MCP16301 features an integrated high-side
N-Channel MOSFET for high efficiency step-down
power conversion. An N-Channel MOSFET is used for
its low resistance and size (instead of a P-Channel
MOSFET). The N-Channel MOSFET gate must be
driven above its source to fully turn on the transistor. A
gate-drive voltage above the input is necessary to turn
on the high side N-Channel. The high side drive voltage
should be between 3.0V and 5.5V. The N-Channel
source is connected to the inductor and Schottky diode,
or switch node. When the switch is off, the inductor cur-
rent flows through the Schottky diode, providing a path
to recharge the boost cap from the boost voltage
source, typically the output voltage for 3.0V to 5.0V out-
put applications. A boost-blocking diode is used to pre-
vent current flow from the boost cap back into the
output during the internal switch-on time. Prior to
startup, the boost cap has no stored charge to drive the
switch. An internal regulator is used to “pre-charge” the
boost cap. Once pre-charged, the switch is turned on
and the inductor current flows. When the switch turns
off, the inductor current free-wheels through the
Schottky diode, providing a path to recharge the boost
cap. Worst case conditions for recharge occur when
the switch turns on for a very short duty cycle at light
load, limiting the inductor current ramp. In this case,
there is a small amount of time for the boost capacitor
to recharge. For high input voltages there is enough
pre-charge current to replace the boost cap charge. For
input voltages above 5.5V typical, the MCP16301
device will regulate the output voltage with no load.
After starting, the MCP16301 will regulate the output
voltage until the input voltage decreases below 4V. See
Figure 2-16
voltage, output voltage and load.
4.2.5
For 3.0V to 5.0V output voltage applications, the boost
supply is typically the output voltage. For applications
with 3.0V < V
can be used.
Alternative boost supplies can be from the input, input
derived, output derived or an auxiliary system voltage.
For low voltage output applications with unregulated
input voltage, a shunt regulator derived from the input
can be used to derive the boost supply. For
applications with high output voltage or regulated high
input voltage, a series regulator can be used to derive
the boost supply.
HIGH SIDE DRIVE
ALTERNATIVE BOOST BIAS
for device range of operation over input
OUT
< 5.0V, an alternative boost supply
MCP16301
DS25004A-page 13