TEA5170 데이터 시트보기 (PDF) - STMicroelectronics

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TEA5170

SWITCH MODE POWER SUPPLY SECONDARY CIRCUIT

STMicroelectronics 

Figure 3

UNSYNCHRONIZED

MODE

Vct

Vtsy

SYNCHRONIZED MODE

TEA5170

UNSYNCHRONIZED

MODE

Vrt

Wtrig- Wtrig+

Remark : In case of an application between

TEA5170 and TEA2164, to optimize the

synchronization windows of these

circuits, the following relations have to

be

used

:

Tm

=

T1S.Y0N6CTe

=

Tm

1.223

with Te : Free period of the TEA2164

oscillator, and Tm : Free period of the

TEA5170 oscillator.

BLOCK DESCRIPTION

The error voltage amplifier inverting-input and out-

put are accessible to use different feed-back net-

work and allowing parasitic filtering network. The

non-inverting input is internaly connected to 2V

reference voltage.

The RC oscillator is designed to work at high

frequency (up to 250kHz). RT sets the capacitor

charging current Io = 2/RT.

The capacitor CT is loaded from V1 ≈ 1V to V2 = 2V

during

T1

=

CT RT

1.985

and

then

down

loaded

through

an integrated resistor R2 ≈ 1kΩ during T2 = 1300 CT

The ramp is used to limit the duty cycle. Then the

maximum duty cycle is

DONMAX

=

T1

1

+

T2

(0.73

T1

+

T2)

The output level is VCC independant when VCC is

over 8V.

The VCC monitoring switches the circuit on when

VCC is over 4V and switches it off when under 3.8V.

This function insures a proper starting procedure

(made by the primary side circuit).

SYNCHRONIZATION

(see Figures 4 and 5)

Figure 4 : Triggering Schematic

VCC

7

Ct

1kΩ

from logic

Network

8

Rt

2.7V

2.7V

+

- towards logic

Figure 5 : Typical Waveforms

Vct

Vrt 2.7V

2V

1V

TtrigP

5/9

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