TEA5170 데이터 시트보기 (PDF) - STMicroelectronics

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TEA5170

SWITCH MODE POWER SUPPLY SECONDARY CIRCUIT

STMicroelectronics 

TEA5170

STARTING

When VCC is under 4V, output pulses are not

allowed and the slave circuit keeps its own mode.

When VCC is going over 4V, output pulses are sent

via the pulse transformer (or an optical device) to

the slave circuit which is synchronizing and enter-

ing the slaved mode. Output pulses can be shut

down only if VCC goes below 3.8 Volt.

Figure 6 : Soft-Start Sequence

VCC (V)

12

SOFT START

Using Csf, it is possible to make a soft start se-

quence. When VCC grows from 0V to 4V, voltage

on Csf equals 0V. When VCC is higher than 4V, Csf

is loaded by a 3.7µA current, then TonMAX (Vcsf)

will vary linearly from Tonmin to Tonmax according

to Csfst bias.

When VCC will go low (3.8 Volt threshold), Csf will

be downloaded by an internal transistor.

4

VCSF (V)

3.2

2

Duty cycle

D on max.

t

t

maximum

D on min.

minimum

t

POWER OUTPUT STAGE

Figure 7 : Electrical Schematic

1mA

VCC

1mA

from logic

3 Pout

6/9

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