RS2042 Orister Corporation, RS2042 Datasheet - Page 5

• Manufacturer Part Number: RS2042
• Description: Green-power Pwm Controller With Freq. Jiggling
• Manufacturer: Orister Corporation

Page No. : 5/8
The threshold voltage decreases if the current IIN increases. A small threshold voltage will force the output GATE drive to terminate earlier,
thus reducing total PWM turn-on time, and making the output power equal to that of the low line input. This proprietary internal compensation
feature ensures a constant output power limit over a wide range of AC input voltages (90VAC to 264VAC).
VDD Over-voltage Protection
VDD over-voltage protection has been built in to prevent damage due to over voltage conditions. When the voltage VDD exceeds the
internal threshold due to abnormal conditions, PWM output will be turned off. Over-voltage conditions are usually caused by open feedback
loops.
Limited Power Control
The FB voltage will increase every time the output of the power supply is shorted or over-loaded. If the FB voltage remains higher than a
built-in threshold for longer than TLPS, PWM output will then be turned off. As PWM output is turned off, the supply voltage VDD will also
begin decreasing.
When VDD goes below the turn-off threshold (eg, 12.4V) the controller will be totally shut down. VDD will be charged up to the turn-on
threshold voltage of 16.5V through the start-up resistor until PWM output is restarted. This protection feature will continue to be activated as
long as the over-loading condition persists. This will prevent the power supply from overheating due to over loading conditions.
Thermal Protection
An external NTC thermistor can be connected from the RT pin to ground. A fixed current IRT is sourced from the RT pin. Because the
impedance of the NTC will decrease at high temperatures, when the voltage of the RT pin drops below 1.065V, PWM output will be disabled.
The RT pin output current is related to the PWM frequency programming resistor RI.
Noise Immunity
Noise from the current sense or the control signal may cause significant pulse width jitter, particularly in continuous-conduction mode. Slope
compensation helps alleviate this problem. Good placement and layout practices should be followed. The designer should avoiding long
PCB traces and component leads. Compensation and filter components should be located near the RS2042. Finally, increasing the power-
MOS gate resistance is advised.
DS-RS2042-03
Dec, 2007
www.Orister.com