ISL1902FAZ-T7A Intersil, ISL1902FAZ-T7A Datasheet - Page 17

• 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

The delay duration is set with a resistor from DELADJ to ground.
Figure 5 on page 12 presents the graphical relationship between
the delay duration and the value of the DELADJ resistance. The
relationship is linear for resistance values greater than ~ 20kΩ
and can be estimated using Equation 24.
t
Soft-Start Operation
Soft-start is not user adjustable and is fixed at ~350ms. Both the
duty cycle and control loop reference have soft-start. This
ensures a well behaved closed loop soft-start that results in
virtually no overshoot.
Biasing
The ISL1902 has a nominal V
15.5V and 7.1V, respectively. The wide hysteresis allows resistive
trickle charging from the high voltage input for start-up bias.
Operating bias is then supplied from another source, such as an
auxiliary transformer winding or in the case of a non-isolated
design, directly from the output or from a tap in the LED string.
The V
design. Unless there is a DC source available, such as the output,
the V
provide bias during the AC voltage valleys and, if used with a
dimmer, provide bias when the dimmer is blocking the AC
voltage each half-cycle.
delay
DD
DD
FIGURE 15. TRICKLE CHARGE START-UP W/AUX. WINDING
≈
73.33
FIGURE 14. QUASI-RESONANT NEAR-ZVS SWITCHING
capacitance must be able to store enough energy to
bypass capacitance value is critical to a successful
WINDING CURRENT
FET D-S VOLTAGE
+
RECTIFIED
RECTIFIED
10.2 R
AC+
AC-
⋅
DELADJ
CR1
C1
R1
CR2
DD
17
(
kΩ
1
start and stop threshold of
VDD
ISL1902
)
ns
24
(EQ. 24)
ISL1902
AC Detection and Reference Generation
The ISL1902 creates a 0V to -0.5V reference for the LED current
control loop (EA reference) by directly measuring the conduction
angle of the AC input voltage. The reference changes only with
conduction angle and is virtually unaffected by variation in either
voltage amplitude or frequency. The ISL1902 is compatible with
both leading and trailing edge modulated dimmers.
The ISL1902 detects the conduction angle using a divider
network across the AC line and connected to the AC pin, although
it can also be located after the AC bridge rectifier.
FIGURE 16. LINEAR REGULATOR START-UP W/AUX. WINDING
R E C TIFIE D
R E C TIFIE D
A C+
A C-
FILTER
EM I
VR 1
FIGURE 17. AC DETECTION
C R1
R 1
C 1
R2
Q 1
1
2
3
4
C R2
1
ISL1902
V D D
IS L1902
G ND
AC
24
23
22
21
20
19
24
March 20, 2013
FN7981.2