TDA4605 Datasheet, PDF (6/21 Pages) STMicroelectronics – CONTROL CIRCUIT FOR SWITCH MODE POWER SUPPLIES USING MOS TRANSISTORS

TDA 4605
Block Diagram
Pin 1
The regulating voltage forwarded to this pin is compared with a stable internal reference voltage V_R
in the regulating and overload amplifier. The output of this stage is ted to the stop comparator.
Pin 2
A voltage proportional to the drain current ot the switching transistor is generated there by the
external RC-combination in conjunction with the primary current transducer. The output of this
transducer is controlled by the logic and referenced to the internal stable voltage V_2B . If the voltage
V₂ exceeds the output voltage of the regulating amplifier, the logic is reset by the stop comparator
and consequently the output ot pin 5 is switched to low potential. Further inputs tor the logic stage
are the output for the start impulse generator with the stable reference potential V_ST and the
supply voltage monitor.
Pin 3
The down-divide primary voltage applied there stabilizes the overload point. In addition the logic is
disabled in the event of low voltage by comparison with the internal stable voltage V_V in the primary
voltage monitor block.
Pin 4
Ground
Pin 5
In the output stage the output signals produced by the logic are shifted to a leved suitable for MOS-
power transistors.
Pin 6
From the supply voltage V₆ are derived a stable internal reference V_REF and the switching threshold
V_6A , V_6E , V_{6 max} and V_{6 min} for the supply voltage monitor. All reference values (V_R , V_2B , V_ST) are
derived from V_REF . If V₆ > V_VE the V_REF is switched on and switched off when V₆ < V_6A . In addition,
the logic is released only for V_{6 min} < V₆ < V_{6 max} .
Pin 7
The output of the overload amplifier is connected to pin 7. A load on this output causes a reduction
in maximal impulse duration. This function can be used to implement a soft start, when pin 7 is
connected to ground by a capacitor.
Semiconductor Group
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