TDA4605 Datasheet, PDF (3/21 Pages) STMicroelectronics – CONTROL CIRCUIT FOR SWITCH MODE POWER SUPPLIES USING MOS TRANSISTORS

TDA 4605
Pin Definitions and Functions
Pin No.
1
2
3
4
5
6
7
8
Function
Regulating Voltage: Information input concerning secondary voltage.
By comparing the regulating voltage - obtained from the regulating winding ot the
transformer - with the internal reference voltage, the output impulse width on pin 5
is adapted to the load ot the secondary side (normal, overload, short-circuit, no
load).
Primary Current Simulation: Information input regarding the primary current.
The primary current rise in the primary winding is simulated at pin 2 as a voltage
rise by means ot external RC-element. When a value is reached that is derived
from the regulating voltage at pin 1, the output impulse at pin 5 is terminated. The
RC-element serves to set the maximum power at the overload point set.
Input for Primary Voltage Monitoring: In the normal operation V₃ is moving
between the thresholds V_3H and V_3L (V_3H > V₃ > V_3L).
V₃ < V_3L: SMPS is switched OFF (line voltage too low).
V₃ > V_3H : Compensation of the overload point regulation (controlled by pin 2)
starts at V_3H : V_3L = 1.7.
Ground
Output: Push-pull-output provides ± 1 A for rapid charge and discharge of the
gate capacitance ot the power MOS-transistor.
Supply Voltage Input: A stable internal reference voltage V_REF is derived from
the supply voltage also the switching thresholds V_6A , V_6E , V_{6 max} and V_{6 min} for
the supply voltage detector. If V₆ > V_6E then V_REF is switched on and swiched off
when V₆ < V_6A . In addition the logic is only enable for V_{6 min} < V₆ < V_{6 max}.
Soft-Start: Input for soft-start. Start-up will begin with short pulses by connecting
a capacitor from pin 7 to ground.
Zero Detector: Input tor the oscillation feedback. After starting oscillation, every
zero transit of the feedback voltage (falling edge) triggers an output impulse at
pin 5. The trigger threshold is at + 50 mV typical.
Semiconductor Group
35