MCP1623 datasheet(12/26 Pages) MICROCHIP

12 / 26 page

MCP1623/24

DS41420A-page 12

 2010 Microchip Technology Inc.

4.2.2

PWM MODE OPERATION

In normal PWM operation, the MCP1623/24 operates

as a fixed frequency, synchronous boost converter. The

switching frequency is internally maintained with a

oscillator typically set to 500 kHz. The MCP1623

device will operate in PWM-only mode even during

periods of light load operation. By operating in

PWM-only mode, the output ripple remains low and the

frequency is constant. Operating in fixed PWM mode

results in lower efficiency during light load operation

(when compared to PFM mode (MCP1624).

Lossless current sensing converts the peak current sig-

nal to a voltage to sum with the internal slope compen-

sation. This summed signal is compared to the voltage

error amplifier output to provide a peak current control

command

for

the

PWM

signal.

The

slope

compensation is adaptive to the input and output

voltage. Therefore, the converter provides the proper

amount of slope compensation to ensure stability, but is

not excessive, which causes a loss of phase margin.

The peak current limit is set to 425 mA typical.

4.2.3

PFM MODE OPERATION

The MCP1624 device is capable of operating in normal

PWM mode and PFM mode to maintain high efficiency

at all loads. In PFM mode, the output ripple has a vari-

able frequency component that changes with the input

voltage and output current. With no load, the quiescent

current draw from the output is typically 19 µA. The

PFM mode can be disabled in selected device options.

PFM operation is initiated if the output load current falls

below an internally programmed threshold. The output

voltage is continuously monitored. When the output

voltage drops below its nominal value, PFM operation

pulses one or several times to bring the output back

into regulation. If the output load current rises above

the upper threshold, the MCP1624 transitions smoothly

into PWM mode.

4.2.4

ADJUSTABLE OUTPUT VOLTAGE

The MCP1623/24 output voltage is adjustable with a

resistor divider over a 2.0V minimum to 5.5V maximum

range. High value resistors are recommended to mini-

mize quiescent current to keep efficiency high at light

loads.

4.2.5

ENABLE/OUTPUT DISCONNECT

The enable pin is used to turn the boost converter on

and off. The enable threshold voltage varies with input

voltage. To enable the boost converter, the EN voltage

level must be greater than 90% of the VIN voltage. To

disable the boost converter, the EN voltage must be

less than 20% of the VIN voltage.

The MCP1623/24 devices incorporate a true output

disconnect feature. With the EN pin pulled low, the

output of the MCP1623/24 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.

4.2.6

INTERNAL BIAS

The MCP1623/24 gets its start-up bias from VIN. Once

the output exceeds the input, bias comes from the

output.

Therefore,

once

started,

operation

completely independent of VIN. Operation is only

limited by the output power level and the input source

series resistance. Once started, the output will remain

in regulation down to 0.35V typical with 1 mA output

current for low source impedance inputs.

4.2.7

INTERNAL COMPENSATION

The error amplifier, with its associated compensation

network, completes the closed loop system by com-

paring the output voltage to a reference at the input of

the error amplifier, and feeding the amplified and

inverted signal to the control input of the inner current

loop. The compensation network provides phase leads

and lags at appropriate frequencies to cancel exces-

sive phase lags and leads of the power circuit. All nec-

essary

compensation

components

and

slope

compensation are integrated.

4.2.8

SHORT CIRCUIT PROTECTION

Unlike most boost converters, the MCP1623/24 allows

its output to be shorted during normal operation. The

internal current limit and overtemperature protection limit

excessive stress and protect the device during periods

of short circuit, overcurrent and overtemperature.

4.2.9

LOW NOISE OPERATION

The MCP1623/24 integrates a low noise anti-ring

switch that damps the oscillations typically observed at

the switch node of a boost converter when operating in

the Discontinuous Inductor Current mode. This

removes the high frequency radiated noise.

4.2.10

OVERTEMPERATURE

PROTECTION

Overtemperature protection circuitry is integrated in the

MCP1623/24. This circuitry monitors the device junction

temperature and shuts the device off if the junction

temperature exceeds the typical +150oC threshold. If

this threshold is exceeded, the device will automatically

restart once the junction temperature drops by 10oC.

The soft start is reset during an overtemperature

condition.

MCP1623 датащи(PDF) 12 Page - Microchip Technology

MCP1623 датащи(HTML) 12 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

датащи скачать

ссылки URL