MCP1642B datasheet(13/32 Pages) MICROCHIP

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 2014 Microchip Technology Inc.

DS20005253A-page 13

MCP1642B/D

4.0

DETAILED DESCRIPTION

4.1

Device Option Overview

The MCP1642B/D family of devices is capable of low

start-up voltage and delivers high efficiency over a wide

load range for single-cell, two-cell, three-cell alkaline,

Ultimate Lithium, NiMH, NiCd and single-cell Li-Ion

battery inputs. A high level of integration lowers total

system cost, eases implementation and reduces board

area.

The devices feature low start-up voltage, fixed and

adjustable output voltage, PWM mode operation,

integrated synchronous switch, internal compensation,

low noise anti-ringing control, inrush current limit and

soft start.

There are two shutdown options for the MCP1642B/D

family:

• True Output Disconnect mode (MCP1642B)

• Input-to-Output Bypass mode (MCP1642D)

4.1.1

TRUE OUTPUT DISCONNECT

MODE OPTION

The MCP1642B device incorporates a true output

disconnect feature. With the EN pin pulled low, the

output of the MCP1642B is isolated or disconnected

from the input by turning off the integrated P-Channel

switch and removing the switch bulk diode connection.

This removes the DC path that is typical in boost

converters, which allows the output to be disconnected

from the input. During this mode, less than 1 µA of

current is consumed from the input (battery). True

output disconnect does not discharge the output.

4.1.2

INPUT-TO-OUTPUT BYPASS MODE

OPTION

The

MCP1642D

device

incorporates

the

Input-to-Output Bypass shutdown option. With the EN

input pulled low, the output is connected to the input

using the internal P-Channel MOSFET. In this mode,

the current drawn from the input (battery) is less than

1 µA with no load. The Input-to-Output Bypass mode is

used when the input voltage is high enough for the load

to operate (e.g. PIC MCU operating in sleep mode).

When a higher regulated output voltage and load

current are necessary, the EN pin must be pulled high,

enabling the boost converter.

4.1.3

ADJUSTABLE OUTPUT VOLTAGE

OPTION

For the MCP1642B/D ADJ option, the output voltage is

adjustable with a resistor divider over a 1.8V minimum

to 5.5V maximum range. The middle point of the

resistor divider connects to the VFB pin. High-value

resistors are recommended to minimize quiescent

current to keep efficiency high at light loads. The

reference voltage is VFB = 1.21V.

4.1.4

FIXED OUTPUT VOLTAGE OPTION

For the fixed output voltage option of the MCP1642B/D

devices, the VFB pin is not connected. There is an

internal feedback divider which minimizes quiescent

current to keep efficiency high at light loads.

The value of the internal divider is 815 k

 typical.

The fixed set values are: 1.8V, 3.0V, 3.3V and 5.0V.

TABLE 4-1:

PART NUMBER SELECTION

BY SHUTDOWN OPTION

Part Number

True Output

Disconnect

Input-to-Output

Bypass

MCP1642B-ADJ

(or -18; 30; 33; 50)

X—

MCP1642D-ADJ

(or -18; 30; 33; 50)

—X

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