HVLED805 Datasheet, PDF (8/29 Pages) STMicroelectronics – Off-line LED driver with primary-sensing

Pin connection
HVLED805
Table 5. 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 typ.) 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 will keep 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 (100nF 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.
5
6
7
8-11
12
ILED
DMG
COMP
N.A
N.C
CC regulation loop reference voltage. An external capacitor will be connected between 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.
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 MOSFET’s 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 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_DMG 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 will be
placed between this pin and GND to achieve stability and good dynamic performance of the
voltage control loop.
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
13 to 16 DRAIN sinks current from this pin as well. Pins connected to the internal metal frame to facilitate heat
dissipation.
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