MCP1631 datasheet(17/34 Pages) MICROCHIP

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DS22063B-page 17

MCP1631/HV/MCP1631V/VHV

4.0

DETAILED DESCRIPTION

4.1

Device Overview

The MCP1631/MCP1631V device family combines the

analog functions to develop high frequency switch

mode power systems while integrating features for

battery charger and LED current source applications.

With the integration of a MOSFET driver, voltage

sense, current sense and over voltage protection, the

MCP1631/MCP1631V is a highly integrated, high-

speed analog pulse width modulator.

The MCP1631/MCP1631V output (VEXT) is used to

control the switch of the power system (on and off

time). By controlling the switch on and off time, the

power system output can be regulated. With the

oscillator and reference voltage as inputs, a simple

interface to a microcontroller is available with the

MCP1631/MCP1631V to develop intelligent power

systems. A good example of an intelligent power

system is a battery charger, programmable LED driver

current source or programmable power supply.

The MCP1631/MCP1631V is a combination of

specialty analog blocks consisting of a Pulse Width

Modulator (PWM), MOSFET Driver, Current Sense

Amplifier

(A2),

Voltage

Sense

Amplifier

(A3),

Overvoltage Comparator (C2) and additional features

(Shutdown, Undervoltage Lockout, Overtemperature

Protection). For the HV options, an internal low dropout

regulator is integrated for operation from high voltage

inputs (MCP1631HV/MCP1631VHV).

4.2

Pulse Width Modulator (PWM)

The internal PWM of the MCP1631/MCP1631V is

comprised of an error amplifier, high-speed comparator

and latch. The output of the amplifier is compared to

either the MCP1631 CS (primary current sense input)

or the MCP1631V VRAMP (voltage mode ramp input) of

the high speed comparator. When the CS or VRAMP

signal reach the level of the error amplifier output, the

on cycle is terminated and the external switch is

latched off until the beginning of the next cycle (high to

low transition of OSCIN).

4.3

VEXT MOSFET Driver

The MCP1631/MCP1631V output can be used to drive

the external MOSFET directly for low side topology

applications. The VEXT is capable of sourcing up to

700 mA and sinking up to 1A of current from a PVDD

source of 5V. Typical output power using the VEXT

output to directly drive the external MOSFET can

exceed 50W depending upon application and switching

frequency.

4.4

Current Sense Amplifier (A2)

The A2 current sense amplifier is used to sense current

in the secondary side of a SEPIC converter or

freewheeling current in a Buck converter. The inverting

amplifier has a built in voltage gain of ten with low offset

and high speed.

4.5

Voltage Sense Amplifier (A3)

The A3 voltage sense amplifier is used to sense battery

voltage. In battery powered applications, it is important

to minimize the steady stage load current draw on the

battery. The voltage sense amplifier (A3) is used to

buffer a high impedance series divider used to reduce

the battery pack voltage to a level that can be read

using an analog to digital converter. The voltage sense

amplifier draws a very low quiescent current and

remains functional when the MCP1631/MCP1631V is

shutdown making it possible to read battery voltage

without turning on the charger.

4.6

Overvoltage Comparator(C2)

The C2 overvoltage comparator is used to prevent the

power system from being damaged when the load

(battery) is disconnected. By comparing the divided

down power train output voltage with a 1.2V internal

reference voltage, the MCP1631/MCP1631V VEXT

output switching is interrupted when the output voltage

is above a pre-set value. This limits the output voltage

of the power train, the 0V comparator’s hysteresis will

operate as a ripple regulator.

4.7

Shutdown Input

The MCP1631/MCP1631V shutdown feature is used to

disable the device with the exception of the voltage

sense amplifier A3 to minimize quiescent current draw.

While shutdown, A3 remains operational while the

device draws 4.4 µA from the input.

4.8

Protection

The MCP1631/MCP1631V has built in Undervoltage

Lockout (UVLO) that ensures the output VEXT pin is

forced to a known state (low) when the input voltage or

AVDD is below the specified value. This prevents the

main MOSFET switch from being turned on during a

power up or down sequence.

The

MCP1631/MCP1631V

provides

thermal

shutdown protection feature, if the internal junction

temperature of the device becomes high, the

overtemperature protection feature will disable (pull the

VEXT output low) and shut down the power train.

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