ALTAIR04-900 Datasheet, PDF (4/29 Pages) STMicroelectronics – Off-line all-primary-sensing switching regulator

Pin connection
2
Pin connection
ALTAIR04-900
Figure 2. Pin connection (top view)
SOURCE 1
SOURCE 2
Vcc 3
GND 4
IREF 5
ZCD/FB 6
COMP 7
N.A. ⁸
16 _DRAIN
15 DRAIN
14 DRAIN
13 _DRAIN
12 N.C.
11 N.A.
10 _N.A.
9 N.A.
Note:
The copper area for heat dissipation has to be designed under the drain pins
Table 1. Pin functions
N.
Name
Function
Power section source and input to the PWM comparator. The current flowing in the MOSFET
is sensed through a resistor connected between the pin and GND. The resulting voltage is
1, 2
SOURCE
compared with an internal reference (0.75V max.) to determine MOSFET’s turn-off. The pin
is equipped with 250 ns blanking time after the gate-drive output goes high for improved
noise immunity. If a second comparison level located at 1V is exceeded the IC is stopped and
restarted after Vcc has dropped below 5V.
Supply voltage of the device. An electrolytic capacitor, connected between this pin and
ground, is initially charged by the internal high-voltage start-up generator; when the device is
3
Vcc
running the same generator keeps it charged in case the voltage supplied by the auxiliary
winding is not sufficient. This feature is disabled in case a protection is tripped. Sometimes a
small bypass capacitor (0.1 µF typ.) to GND might be useful to get a clean bias voltage for
the signal part of the IC.
Ground. Current return for both the signal part of the IC and the gate drive. All of the ground
4
GND connections of the bias components should be tied to a trace going to this pin and kept
separate from any pulsed current return.
CC regulation loop reference voltage. An external capacitor has to be connected between
5
IREF
this pin and GND. An internal circuit develops a voltage on this capacitor that is used as the
reference for the MOSFET’s peak drain current during CC regulation. The voltage is
automatically adjusted to keep the average output current constant.
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Doc ID 18211 Rev 2