TDA4605 datasheet(4/6 Pages) STMICROELECTRONICS

4 / 6 page

ELECTRICAL CHARACTERISTICS (VCC = 10V, Tamb =25

oC, unless otherwise specified) (continued)

Symbol

Parameter

Test Conditions

Min.

Typ.

Max.

Unit

GENERALLY VALID DATA (V6 = 10V)

VOLTAGE OF THE ZERO Transition DETECTOR

V8P

Positive Clamping Voltage

I8 = 1mA

0.75

V8N

Negative Clamping Voltage

I8 = -1mA

-0.2

V8S

Threshold Value

TUL

Suppression of Transformer Ringing

3.8

4.5

µs

-I8

Input Current

V8 =0

µV

PUSH-PULL OUTPUT STAGE

SATURATION VOLTAGES

VSatU

Pin 5 Sourcing

I5 = -0.1A

1.5

2.0

VSatU

Pin 5 Sinking

I5 = +0.1A

1.0

1.2

VSatU

Pin 5 Sinking

I5 = +0.5A

1.4

1.8

OUTPUT SLOW RATE

+dV5/dt

Rising Edge

µs

-dV5/dt

Falling Edge

100

µs

REDUCTION OF CONTROL VOLTAGE

-I1

Current to reduce the Control Voltage

V7 =1V

µA

PROTECTION CIRCUIT

V6(Min.)

Undervoltage Protection for V6 :

Voltage at Pin 5 = V5(Min.) if V6 <V6(Min.)

7.0

7.25

7.5

V6(Max.)

Overvoltage Protection for V6 :

Voltage at Pin 5 = V5(Min.) if V6 >V6(Max.)

16.5

V3A

Undervoltage Protection for VAC :

Voltage at Pin 5 = V5(Min.) if V3 <V3A

V2 = 0V

970

1005

1040

Over Temperature : at the given chip temperature the

IC will switch V5 to V5(Min.)

150

V3Sat

Voltage at Pin 3 if one of the protection functions was

triggered ; (V3 will be clamped until V6 <V6A)

I3 = 750

µA

0.4

0.8

Current Drain during Burst Operation

V3 =V2 =0V

FUNCTIONAL DESCRIPTION

In free running fly-back converters, the TDA4605

assumes control of a MOS power transistor and all

necessary regulation and monitoring functions.

The serial circuit of power transistor and primary

winding of the flyback transformer is connected to

the input voltage. During the switch-on period of the

transistor, energy is stored in the transformer and

during the switch-off period it is fed to te load via

the secondary winding. By varing the switch-on

time of the power transistor, the IC controls each

portion of energy transferred to the secondary side

such that the output voltage remains nearly inde-

pendent of load variations.

The required control information is taken from the

input voltage during the switch-on period and from

a regulation winding during the switch-off period. A

new cycle begins as soon as the energy stored in

the transformer has been totally delivered to the

secondary side.

In different load ranges, the SMPS will behave as

follows :

- No-Load Operation : The power supply unit

oscillates in non continuous mode at a typical

frequency of 20 to 40kHz. Depending upon the

transformer winding and the regulated voltage

divider, the output voltage can be slightly above

the nominal value.

- Normal Operation : Starting from typ. 200kHz,

the switching frequency falls with increasing load

and decreasing AC voltage. The duty cycle de-

pends primarily on the AC voltage. The output

voltage is only slightly load-dependen t.

- OverloadPoint : Maximum output power is avail-

able at this point of the output characteristics

- Overload : The energy transferred per operation

cycle is limited at the top. Therefore, the output

voltage will fall with secondary oveloading.

TDA4605

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