TOP242R POWERINT [Power Integrations, Inc.], TOP242R Datasheet - Page 8

• Manufacturer Part Number: TOP242R
• Description: TOPSwitch -GX Family Extended Power, Design Flexible, EcoSmart, Integrated Off-line Switcher
• Manufacturer: POWERINT [Power Integrations, Inc.]

CURRENT LIMIT (X) pin (Y, R or F package) or MULTI-
FUNCTION (M) pin (P or G package) and the rectified DC
high voltage bus, the current limit is reduced with increasing
line voltage, allowing a true power limiting operation against
line variation to be implemented. When using an RCD clamp,
this power limiting technique reduces maximum clamp
voltage at high line. This allows for higher reflected voltage
designs as well as reducing clamp dissipation.
The leading edge blanking circuit inhibits the current limit
comparator for a short time after the output MOSFET is turned
on. The leading edge blanking time has been set so that, if a
power supply is designed properly, current spikes caused by
primary-side capacitances and secondary-side rectifier reverse
recovery time should not cause premature termination of the
switching pulse.
The current limit is lower for a short period after the leading
edge blanking time as shown in Figure 52. This is due to
dynamic characteristics of the MOSFET. To avoid triggering
the current limit in normal operation, the drain current wave-
form should stay within the envelope shown.
Line Under-Voltage Detection (UV)
At power up, UV keeps TOPSwitch-GX off until the input line
voltage reaches the under voltage threshold. At power down,
UV prevents auto-restart attempts after the output goes out of
regulation. This eliminates power down glitches caused by
the slow discharge of large input storage capacitor present in
applications such as standby supplies. A single resistor
connected from the LINE-SENSE pin (Y, R or F package) or
MULTI-FUNCTION pin (P or G package) to the rectified DC
high voltage bus sets UV threshold during power up. Once the
power supply is successfully turned on, the UV threshold is
lowered to 40% of the initial UV threshold to allow extended
Figure 10. Synchronization Timing Diagram.
8
TOP242-250
X, L or M Pin (STOP)
G
1/02
Enable from
Oscillator
(SAW)
D MAX
input voltage operating range (UV low threshold). If the UV
low threshold is reached during operation without the power
supply losing regulation the device will turn off and stay off
until UV (high threshold) has been reached again. If the power
supply loses regulation before reaching the UV low threshold,
the device will enter auto-restart. At the end of each auto-
restart cycle (S7), the UV comparator is enabled. If the UV high
threshold is not exceeded the MOSFET will be disabled during
the next cycle (see Figure 8). The UV feature can be disabled
independent of OV feature as shown in Figures 19 and 23.
Line Overvoltage Shutdown (OV)
The same resistor used for UV also sets an overvoltage thresh-
old which, once exceeded, will force TOPSwitch-GX output
into off-state. The ratio of OV and UV thresholds is preset at
4.5 as can be seen in Figure 11. When the MOSFET is off, the
rectified DC high voltage surge capability is increased to the
voltage rating of the MOSFET (700 V), due to the absence of
the reflected voltage and leakage spikes on the drain. A small
amount of hysteresis is provided on the OV threshold to
prevent noise triggering. The OV feature can be disabled
independent of the UV feature as shown in Figures 18 and 32.
Line Feed Forward with DC
The same resistor used for UV and OV also implements line
voltage feed forward which minimizes output line ripple and
reduces power supply output sensitivity to line transients. This
feed forward operation is illustrated in Figure 7 by the
different values of I
age). Note that for the same CONTROL pin current, higher
line voltage results in smaller operating duty cycle. As an added
feature, the maximum duty cycle DC
78% (typical) at a voltage slightly higher than the UV thresh-
old to 38% (typical) at the OV threshold (see Figures 7 and
11). Limiting DC
MAX
L
at higher line voltages helps prevent trans-
(Y, R or F package) or I
MAX
Reduction
MAX
is also reduced from
Time
M
(P or G Pack-
PI-2637-060600