MCP1640 查看數據表（PDF） - Microchip Technology

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MCP1640

0.65V Start-up Synchronous Boost Regulator with True Output Disconnect or Input/Output Bypass Option

Microchip Technology 

4.0 DETAILED DESCRIPTION

4.1 Device Option Overview

The MCP1640/B/C/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, 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, adjustable

output voltage, PWM/PFM mode operation, low IQ,

integrated synchronous switch, internal compensation,

low noise anti-ring control, inrush current limit and soft

start. There are two feature options for the MCP1640/

B/C/D family: PWM/PFM mode or PWM mode only,

and “true output disconnect” or input bypass.

4.1.1 PWM/PFM MODE OPTION

The MCP1640/C devices use an automatic switchover

from PWM to PFM mode for light load conditions to

maximize efficiency over a wide range of output

current. During PFM mode, higher peak current is used

to pump the output up to the threshold limit. While

operating in PFM or PWM mode, the P-Channel switch

is used as a synchronous rectifier, turning off when the

inductor current reaches 0 mA to maximize efficiency.

In PFM mode, a comparator is used to terminate

switching when the output voltage reaches the upper

threshold limit. Once switching has terminated, the

output voltage will decay or coast down. During this

period, very low IQ is consumed from the device and

input source, which keeps power efficiency high at light

load. The disadvantages of PWM/PFM mode are

higher output ripple voltage and variable PFM mode

frequency. The PFM mode frequency is a function of

input voltage, output voltage and load. While in PFM

mode, the boost converter pumps the output up at a

switching frequency of 500 kHz.

4.1.2 PWM MODE ONLY OPTION

The MCP1640B/D devices disable PFM mode

switching, and operate only in PWM mode over the

entire load range. During periods of light load opera-

tion, the MCP1640B/D continues to operate at a con-

stant 500 kHz switching frequency keeping the output

ripple voltage lower than PFM mode. During PWM only

mode, the MCP1640B/D P-Channel switch acts as a

synchronous rectifier by turning off to prevent reverse

current flow from the output cap back to the input in

order to keep efficiency high. For noise immunity, the

N-Channel MOSFET current sense is blanked for

approximately 100 ns. With a typical minimum duty

cycle of 100 ns, the MCP1640B/D continues to switch

at a constant frequency under light load conditions.

Figure 2-12 represents the input voltage versus load

current for the pulse skipping threshold in PWM only

mode. At lighter loads, the MCP1640B/D devices begin

to skip pulses.

 2010 Microchip Technology Inc.

MCP1640/B/C/D

4.1.3

TRUE OUTPUT DISCONNECT

OPTION

The MCP1640/B devices incorporate a true output

disconnect feature. With the EN pin pulled low, the

output of the MCP1640/B 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 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 discon-

nect does not discharge the output; the output voltage

is held up by the external COUT capacitance.

4.1.4 INPUT BYPASS OPTION

The MCP1640C/D devices incorporate the input

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 draw

from the input (battery) is less than 1 µA with no load.

The Input Bypass mode is used when the input voltage

range is high enough for the load to operate in Sleep or

low IQ mode. When a higher regulated output voltage is

necessary to operate the application, the EN input is

pulled high enabling the boost converter.

TABLE 4-1: PART NUMBER SELECTION

Part

Number

PWM/

PFM

PWM True Dis Bypass

MCP1640

X

X

MCP1640B

X

X

MCP1640C

X

X

MCP1640D

X

X

DS22234A-page 11

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