ALTAIR04-900 Datasheet, PDF (5/29 Pages) STMicroelectronics – Off-line all-primary-sensing switching regulator

ALTAIR04-900
Pin connection
Table 1. Pin functions (continued)
N.
Name
Function
Transformer’s demagnetization sensing for quasi-resonant operation. Input/output voltage
monitor. A negative-going edge triggers MOSFET’s turn-on. The current sourced by the pin
during ON-time is monitored to get an image of the input voltage to the converter, in order to
compensate the internal delay of the current sensing circuit and achieve a CC regulation
independent of the mains voltage. If this current does not exceed 50µA, either a floating pin
6
ZCD/FB
or an abnormally low input voltage is assumed, the device is stopped and restarted after Vcc
has dropped below 5V. Still, the pin voltage is sampled-and-held right at the end of
transformer’s demagnetization to get an accurate image of the output voltage to be fed to the
inverting input of the internal, transconductance-type, error amplifier, whose non-inverting
input is referenced to 2.5V. Please note that the maximum I_ZCD/FB sunk/sourced current has
to not exceed ±2 mA (AMR) in all the Vin range conditions. No capacitor is allowed between
the pin and the auxiliary transformer.
Output of the internal transconductance error amplifier. The compensation network is placed
7
COMP between this pin and GND to achieve stability and good dynamic performance of the voltage
control loop.
8-11
12
13 to 16
N.A
N.C
DRAIN
Not available. These pins must be left not connected
Not internally connected. Provision for clearance on the PCB to meet safety requirements.
Drain connection of the internal power section. The internal high-voltage start-up generator
sinks current from this pin as well. Pins connected to the internal metal frame to facilitate
heat dissipation.
Doc ID 18211 Rev 2
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