MCP16251_16 datasheet(10/32 Pages) MICROCHIP

Part #	MCP16251

Description	Low Quiescent Current, PFM/PWM Synchronous Boost Regulator with True Output Disconnect or Input/Output Bypass Option

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Manufacturer	MICROCHIP [Microchip Technology]

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MCP16251/2

DS20005173B-page 10

 2013 - 2016 Microchip Technology Inc.

4.0

DETAILED DESCRIPTION

4.1

Device Overview

The MCP16251/2 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 quiescent current, low start-up voltage,

adjustable output voltage, PWM/PFM mode operation,

integrated synchronous switch, internal compensation,

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

start. There are two options for the MCP16251/2 family:

True Output Disconnect and Input-to-Output Bypass

(see Table 4-1).

4.1.1

PFM/PWM OPERATION

The MCP16251/2 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, a controlled 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, which is called Sleep period, 1 µA is typically

consumed from the input source, which keeps power

efficiency high at light load. PWM/PFM mode has

higher output ripple voltage than PWM mode, and

variable frequency. The PFM mode frequency is a

function of input voltage, output voltage and load. While

in PFM mode, the boost converter periodically pumps

the output with a fixed switching frequency of 500 kHz.

Figure 2-17 represents the load current versus input

voltage for the PFM-to-PWM threshold.

4.1.2

TRUE OUTPUT DISCONNECT

OPTION

The MCP16251 device incorporates a true output

disconnect feature. With the EN pin pulled low, the

output of the MCP16251 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 0.6 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.

4.1.3

INPUT BYPASS OPTION

The MCP16252 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 draw

from the input (battery) is less than 0.6 µA with no load.

The Input Bypass mode is used when the input voltage

range is high enough for the load to operate in Standby

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.

In this mode, the current through the P-Channel

MOSFET must not be higher than 400 mA.

TABLE 4-1:

PART NUMBER SELECTION

Part

Number

True Output

Disconnect

Input-to-Output

Bypass

MCP16251

✓

—

MCP16252

—

✓

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