ISL1902FAZ-T7A Intersil, ISL1902FAZ-T7A Datasheet - Page 23

• Manufacturer Part Number: ISL1902FAZ-T7A
• Description: LED Lighting Drivers Dimmable AC Mains LED Driver PFC
• Manufacturer: Intersil

Specifications of ISL1902FAZ-T7A

• Rohs: yes
• Input Voltage: 4 V
• Operating Frequency: 320 Hz
• Maximum Supply Current: 14.5 mA
• Output Current: 1 A
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Package / Case: QSOP-24
• Minimum Operating Temperature: - 40 C

PRELOAD Signal
PRELOAD is a digital signal used to control an external FET that
discharges the output capacitance if AC is low for more than
~30ms, or if REFIN drops below the OFFREF threshold. This
feature prevents the output capacitor from providing load current
for an extended period of time after the converter is disabled.
Otherwise, the output will dim as the output capacitance slowly
discharges through the LEDs. This process can take a significant
amount of time, resulting in “afterglow”, unless supplemental
discharge methods are used. The advantage of PRELOAD over a
non-switched resistive load is efficiency improvement. Examples
of PRELOAD usage may be found on pages 5 through 7 in the
“Typical Applications”.
In-rush Control
The ISL1902 features a AC half-cycle-by-half-cycle in-rush control
signal. Due to the capacitive input of DC/DC converters operating
with a leading edge modulated AC line dimmer, there is an input
current spike every half-cycle when the AC line dimmer turns on,
particularly so when conduction begins near the AC peak. The
current spike is normally attenuated with a resistor in series with
the AC line. The resistor is always present and dissipates power
even at full dimmer conduction.
The ISL1902 provides a control signal, INRUSH, which may be
used to gate an external switch, such as a triac to bypass the
in-rush limiting resistor after the in-rush event is over. The signal
is low when the IC detects the absence of AC line voltage. When
enabled, approximately 150µs after AC voltage is detected,
IN-RUSH outputs an 80kHz square wave. This may be coupled
through a pulse transformer or other isolation device to allow
control of a level shifted device. Examples of using INRUSH can
be found in the “Typical Applications” on pages 5 and 7. Another
example is shown in Figure 33.
AC
FIGURE 33. INRUSH EXAMPLE USING A PHOTO-TRIAC
23
FILTER
EMI
INRUSH
ISL1902
Gate Drive
The ISL1902 output is capable of sourcing and sinking 1.5A. The
typical ON-resistance of the outputs is 12Ω. The OUT high level is
limited to the OUT clamp voltage or V
Thermal Protection
Internal die over-temperature protection is provided. An
integrated temperature sensor protects the device should the
junction temperature exceed +150°C. There is approximately
+25°C of hysteresis.
Ground Plane Requirements
Careful layout is essential for satisfactory operation of the device.
A good ground plane must be employed. V
be bypassed directly to GND with good high frequency
capacitance.
DD
, whichever is lower.
DD
and VREF should
March 20, 2013
FN7981.2