M51996AP データシートの表示（PDF） - MITSUBISHI ELECTRIC

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M51996AP

SWITCHING REGULATOR CONTROL

MITSUBISHI ELECTRIC  

MITSUBISHI (Dig./Ana. INTERFACE)

M51996AP/FP

SWITCHING REGULATOR CONTROL

Start-up circuit section

The start-up current is such low current level as typical 100µ

A,as shown in Fig.3,when the Vcc voltage is increased

from low level to start-up voltage Vcc(START).

In this voltage range,only a few parts in this IC,which has the

function to make the output voltage low level,is alive and

Icc current is used to keep output low level.The large voltage

difference between Vcc(START) and Vcc(STOP) makes start-up

easy,because it takes rather long duration from Vcc(START) to

Vcc(STOP).

Icco

~ 11mA

IccL

~ 100µA

Vcc Vcc

(STOP) (START)

~ 9.9V ~ 16.2V

SUPPLY VOLTAGE Vcc(V)

Fig.3 Circuit current vs.supply voltage

Oscillator section

The oscillation waveform is the triangle one.The ON-duration

of output pulse depends on the rising duration of the triangle

waveform and dead-time is decided by the falling duration.

The rising duration is determined by the product of external

resistor RON and capacitor CF and the falling duration is mainly

determined by the product of resistor ROFF and capacitor CF.

(1)Oscillator operation when SOFT circuit does

not operate

Fig.4 shows the equivalent charging and discharging circuit

diagram of oscillator.

The current flows through RON from the constant voltage source

of 5.8V.CF is charged up by the same amplitude as RON

current,when internal switch SW1,SW2 is switched to "charging

side".The rise rate of CF terminal is given as

~ VT - ON

RON X CF

(V/s)

................................................(1)

~ where VT - ON 4.5V

The maximum on duration is approximately given as

~ (VOSCH-VOSCL) X

VT - ON

RON

X

CF

(s)........................(2)

~ where VOSCH 4.4V

~ VOSCL 2.0V

CF is discharged by the summed-up of ROFF current and one

sixteenth (1/16) of RON current by the function of Q2,Q3 and Q4

when SW1,SW2 are switched to "discharge side".

RON

T-ON

5.8V

Q4

Q1

1/16

Q3

CHARGING

SW1

ROFF

CF

T-OFF

CF

M51996A

FROM

VF SIGNAL

Vz ~ 4.2V

SWITCHED BY

CHARGING AND

DISCHARGING

SIGNAL

SW2

Q2

DISCHARGING

Fig.4 Schematic diagram of charging and discharging

control circuit for OSC.capacitor CF

VOSCH

~ 4.4V

VOSCL

~ 2.0V

VOH

VOL

Fig.5 OSC.waveform at normal condition (no-

operation of intermittent action and OSC.control

circuit)

So fall rate of CF terminal is given as

~ VT - OFF

ROFF X CF

+

16

VT - ON

X RON X

CF

(V/s)

.....................(3)

The minimum off duration approximately is given as

~ (VOSCH-VOSCL) X CF

VT-OFF + VT-ON

(s) .....................................(4)

ROFF 16 X RON

~ where VT - OFF 3.5V

The cycle time of oscillation is given by the summation of

Equations 2 and 4.

The frequency including the dead-time is not influenced by the

temperature because of the built-in temperature compensating

circuit.

( 10 / 22 )

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