MCP1661 datasheet(14/34 Pages) MICROCHIP

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MCP1661

DS20005315B-page 14

 2014-2015 Microchip Technology Inc.

4.2.7

ENABLE PIN

The MCP1661 device is enabled when the EN pin is set

high. The device is put into Shutdown mode when the

EN pin is set low. To enable the boost converter, the EN

voltage level must be greater than 85% of the VIN

voltage. To disable the boost converter, the EN voltage

must be less than 7.5% of the VIN voltage.

In Shutdown mode, the MCP1661 device stops

switching and all internal control circuitry is switched

off. On boost configuration, the input voltage will be

bypassed to output through the inductor and the

Schottky diode. In the SEPIC converter, Shutdown

mode acts as output disconnect.

4.2.8

INTERNAL COMPENSATION

The error amplifier, with its associated compensation

network, completes the closed-loop system by

comparing the output voltage to a reference at the

input of the error amplifier and by feeding the amplified

and inverted error voltage to the control input of the

inner current loop. The compensation network

provides phase leads and lags at appropriate

frequencies to cancel excessive phase lags and leads

of the power circuit. All necessary compensation

components and slope compensation are integrated.

4.2.9

OUTPUT OVERVOLTAGE

PROTECTION (OVP)

An internal VFB fault signal turns off the PWM signal

(VEXT) and prevents the output from going out of

regulation in the event of:

• short circuit of the feedback pin to GND

• disconnection of the feedback divider from VOUT

In any of the above events, for a regular integrated

boost circuit (IC) without any protection implemented, if

the VFB voltage drops to ground potential, its N-channel

transistor will be forced to switch at full duty cycle and

VOUT rises. This Fault event may cause the SW pin to

exceed its maximum voltage rating and may damage

the boost regulator IC, the external components and

the load. To avoid all these, MCP1661 has

implemented an overvoltage protection (OVP) which

turns off PWM switching when an overvoltage condition

is detected. There is an overvoltage comparator with

80 mV reference which monitors the VFB voltage.

The OVP comparator is disabled during start-up

sequences and thermal shutdown.

If OVP occurs with the input voltage below the

UVLOSTART threshold and VFB remains under 80 mV

due to a low input voltage or overload condition, the

device latches its output and resumes after restart.

4.2.10

OVERCURRENT LIMIT

The MCP1661 device uses a 1.3A cycle-by-cycle

inductor peak current limit to protect the N-channel

switch. There is an overcurrent comparator which

resets the drive latch when the peak of the inductor

current reaches the limit. In current limitation, the

output voltage starts dropping.

4.2.11

OUTPUT SHORT CIRCUIT

CONDITION

Like all non-synchronous boost converters, the MCP1661

inductor current will increase excessively during a short

circuit on the converter’s output. Short circuit on the

output will cause the diode rectifier to fail and the

inductor’s temperature to rise. When the diode fails, the

SW pin becomes a high-impedance node, it remains

connected only to the inductor and the excessive resulted

ringing will damage the MCP1661 device.

4.2.12

OVERTEMPERATURE

PROTECTION

Overtemperature protection circuitry is integrated into

the MCP1661 device. This circuitry monitors the device

junction temperature and shuts the device off if the

junction temperature exceeds the typical +150°C

threshold. If this threshold is exceeded, the device will

automatically restart when the junction temperature

drops by 15°C. The output overvoltage protection

(OVP) is reset during an overtemperature condition.

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