MCP1601_13 datasheet(11/24 Pages) MICROCHIP

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DS21762B-page 11

MCP1601

4.2

Cross-Conduction Timing

Proper timing between turning on the P-Channel, high-

side MOSFET and turning off the N-Channel, low-side

MOSFET (and vice versa) is critical to obtaining high

efficiency. This delay between transitions is what limits

the maximum duty cycle obtainable by the MCP1601.

The delay between transitions leads to more time when

the external inductor current is freewheeling through

the internal N-Channel body diode and leads to a

decrease in efficiency. If the timing delay is too short

and both the internal P-Channel MOSFET and N-

Channel MOSFET conduct, high peak currents will be

observed shooting through the device. This will also

reduce the operating efficiency. The MCP1601 inset

timing is integrated to optimize efficiency for the entire

line and load operating range of the device.

4.3

Integrated Protection Features

4.3.1

SHUTDOWN

By placing a logic low on the SHDN pin of the

MCP1601, the device will enter a low quiescent current

shutdown mode. This feature turns off all of the internal

bias and drivers within the MCP1601 in an effort to min-

imize the quiescent current. This feature is popular for

battery-operated, portable power applications. The

shutdown low quiescent current is typically 1 µA.

4.3.2

INTERNAL OSCILLATOR AND

SYNCHRONIZATION CAPABILITY

The internal oscillator is completely integrated and

requires no external components. The frequency is set

nominally to 750 kHZ in an effort to minimize the exter-

nal inductor and capacitor size needed for the BUCK

topology. In addition to the internal 750 kHz oscillator,

the MCP1601 is capable of being synchronized to an

external oscillator. The external oscillator frequency

must be greater than 850 kHz and less than 1 MHz. For

proper synchronization, the duty cycle of the external

synchronization clock must be between 10% and 90%.

The minimum low voltage level should be below 15% of

VIN and the high level of the clock should be above

45% of VIN. Rise and fall time requirements for the

external synchronization clock must be faster than

100 ns from 10% to 90%. When synchronizing to an

external clock, the MCP1601 will always operate in the

PWM mode in an effort to eliminate multiple switching

frequency’s and their harmonics.

4.3.3

INTERNAL SOFT START

The MCP1601 completely integrates the soft start func-

tion and requires no external components. The soft

start time is typically 0.5 ms and is reset during over-

current and over-temperature shutdown.

4.3.4

OVER-TEMPERATURE

PROTECTION

The MCP1601 protects the internal circuitry from over-

temperature conditions by sensing the internal device

temperature and shutting down when it reaches

approximately 160°C. The device will shut down, the

temperature will cool to approximately 150°C, soft start

will be enabled and normal operation will resume with

no external circuit intervention.

4.3.5

UNDER-VOLTAGE LOCKOUT

Protection from operating at sustained input voltages

that are out of range is prevented with the integrated

Under-Voltage Lockout feature. When the input voltage

dips below 2.5V (typically), the MCP1601 will shutdown

and the soft start circuit will be reset. Normal operation

will resume when the input voltage is elevated above

2.7V, maximum. This hysteresis is provided to prevent

the device from starting with too low of an input voltage.

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