MB39C015 datasheet(8/43 Pages) CYPRESS

8 / 43 page

MB39C015

Document Number: 002-08364 Rev. *A

Page 8 of 43

5. Function of Each Block

■ PWM Logic control circuit

The built-in P-ch and N-ch MOS FETs are controlled for synchronization rectification according to the frequency (2.0 MHz) oscillated

from the built-in oscillator (square wave oscillation circuit).

■ IOUT Comparator circuit

This circuit detects the current (ILX) which flows to the external inductor from the built-in P-ch MOS FET. By comparing VIDET obtained

through I-V conversion of peak current IPK of ILX with the Error Amp output, the built-in P-ch MOS FET is turned off via the PWM Logic

Control circuit.

■ Error Amp phase compensation circuit

This circuit compares the output voltage to reference voltages such as VREF. This IC has a built-in phase compensation circuit that

is designed to optimize the operation of this IC.This needs neither to be considered nor addition of a phase compensation circuit and

an external phase compensation device.

■ VREF circuit

A high accuracy reference voltage is generated with BGR (bandgap reference) circuit. The output voltage is 1.30 V (Typ).

■ Voltage Detection (VDET) circuit

The voltage detection circuit monitors the voltage at the VDET pin. Normally, use the XPOR pin through pull-up with an external

resistor. When the VDET pin voltage reaches 0.6 V, it reaches the H level.

Timing chart example : (XPOR pin pulled up to VIN)

■ Protection circuit

This IC has a built-in over-temperature protection circuit. The over-temperature protection circuit turns off both N-ch and P-ch switching

FETs when the junction temperature reaches

 135 °C . When the junction temperature comes down to  110 °C , the switching FET

is returned to the normal operation. Since the PWM control circuit of this IC is in the control method in current mode, the current peak

value is also monitored and controlled as required.

VIN

CTLP

VDET

XPOR

VUVLO

VTHHPR

VTHLPR

VUVLO : UVLO threshold voltage

VTHHPR, VTHLPR : XPOR threshold voltage

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