MCP1640B-I View Datasheet(PDF) - Microchip Technology

Part Name

Description

Manufacturer

MCP1640B-I

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

Microchip Technology 

MCP1640/B/C/D

4.2 Functional Description

The MCP1640/B/C/D is a compact, high-efficiency,

fixed frequency, step-up DC-DC converter that

provides an easy-to-use power supply solution for

applications powered by either one-cell, two-cell, or

three-cell alkaline, NiCd, or NiMH, or one-cell Li-Ion or

Li-Polymer batteries.

VOUT

Figure 4-1 depicts the functional block diagram of the

MCP1640/B/C/D.

VIN

SW

EN

INTERNAL

BIAS

GATE DRIVE

AND

SHUTDOWN

CONTROL

LOGIC

DIRECTION

CONTROL

IZERO

SOFT-START

.3V

0V

ILIMIT

ISENSE

GND

OSCILLATOR

SLOPE

COMP.



PWM/PFM

LOGIC

FIGURE 4-1:

MCP1640/B/C/D Block Diagram.

4.2.1 LOW-VOLTAGE START-UP

The MCP1640/B/C/D is capable of starting from a low

input voltage. Start-up voltage is typically 0.65V for a

3.3V output and 1 mA resistive load.

When enabled, the internal start-up logic turns the

rectifying P-Channel switch on until the output

capacitor is charged to a value close to the input

voltage. The rectifying switch is current limited during

this time. After charging the output capacitor to the

input voltage, the device starts switching. If the input

voltage is below 1.6V, the device runs open-loop with a

fixed duty cycle of 70% until the output reaches 1.6V.

During this time, the boost switch current is limited to

1.21V

FB

EA

50% of its nominal value. Once the output voltage

reaches 1.6V, normal closed-loop PWM operation is

initiated.

The MCP1640/B/C/D charges an internal capacitor

with a very weak current source. The voltage on this

capacitor, in turn, slowly ramps the current limit of the

boost switch to its nominal value. The soft-start

capacitor is completely discharged in the event of a

commanded shutdown or a thermal shutdown.

There is no undervoltage lockout feature for the

MCP1640/B/C/D. The device will start up at the lowest

possible voltage and run down to the lowest possible

voltage. For typical battery applications, this may result

in “motor-boating” for deeply discharged batteries.

DS22234A-page 12

 2010 Microchip Technology Inc.

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