TDA4605-2 Datasheet, PDF (8/23 Pages) Siemens Semiconductor Group – Control IC for Switched-Mode Power Supplies using MOS-Transistors

TDA 4605-2
Block Diagram
Pin 1
In the control and overload amplifier the control voltage applied to this pin is compared with a stable
internal reference voltage V. The output signal of this stage is fed to the "stop" comparator. If the
control voltage is rather small at pin 1 an additional current is added by means of current source
which is controlled according the level at pin 7. This additional current is virtually reducing the
control voltage present at pin 1.
Pin 2
A voltage proportional to the drain current of the switching transistor is generated by means of an
external RC-combination in conjunction with the internal functional block primary current / voltage
converter. The output of this converter is controlled by the internal functional block "logic" and is
also connected to the internal reference voltage V_2B . If the voltage V₂ exceeds the output voltage
of the "control and overload amplifier" the stop comparator will reset the control logic. Consequently
the output of pin 5 is switched to low potential. Further inputs for the logic stage are the outputs of
the start impulse generator with the stable reference potential V_ST , the supply voltage monitoring
circuit as well as the primary voltage supervision circuit.
Pin 3
The primary voltage applied here via a voltage divider is used to stabilize the fold-back point. In
addition the logic is disable if - in comparison with the internal reference voltage V_V - a mains
undervoltage condition is detected.
Pin 4
Ground
Pin 5
In the output stage the output signals from the "logic" block are converted into driving signals
suitable for power MOS-transistors.
Pin 6
From the supply voltage V₆ applied to this pin internally a stable reference voltage V_REF as well as
the switching threshold V_6A , V_6E , V_{6 max} and V_{6 min} , for the supply voltage monitor section of the IC.
All other inter reference value (V_R , V_2B , V_ST and V_v) are derived for V_REF . If V₆ > V_6E the V_REF
voltage source is switched on and the source is switched off if V₆ < V_6A . In addition the logic is
enable only if V_{6 min} < V₆ < V_{6 max} .
Version 2.0
8
1 Jul 2002