ISL1902 Datasheet, PDF (2/25 Pages) Intersil Corporation – Full-Featured, Dimmable AC Mains LED Driver with PFC

ISL1902
Pin Configuration
ISL1902
(24 LD QSOP
TOP VIEW
VDD 1
PRELOAD 2
OFFREF 3
VREF 4
IOUT 5
CS+ 6
CS- 7
REFIN 8
LPOUT 9
OC 10
FB2 11
FB1 12
24 OUT
23 PWMOUT
22 INRUSH
21 GND
20 AC
19 OVP
18 LOUT
17 LREF
16 LFB
15 RAMP
14 VERR
13 DELADJ
Pin Descriptions
PIN # SYMBOL
DESCRIPTION
1
VDD VDD is the power connection for the IC. To optimize noise immunity, bypass VDD to GND with a ceramic capacitor as close to the VDD
and GND pins as possible.
2 PRELOAD The output control signal to drive an external FET placed in parallel with the LED load. This feature allows the output capacitor to be
quickly discharged to prevent continued low level illumination of the LEDs due to stored energy in the output capacitor.
3 OFFREF Sets the reference level to disable the driver at light loading. The turn-off reference can be set at any level between 0V and 0.6V,
corresponding to 0% to 100% of output loading. This feature is normally used in triac-based wall dimmer applications to disable the
output before the dimmer becomes unstable due to insufficient holding current. OFFREF triggers PRELOAD to discharge the output
capacitance with an external FET.
4
VREF The 5.40V reference voltage output having ±100mV tolerance over line, load and operating temperature. Bypass to GND with a 0.1µF
to 3.3µF low ESR capacitor.
5
IOUT The output of the differential current sensing circuit. A pair of resistors and capacitors is placed on this output to form two low pass
filters. IOUT creates the current feedback signals for the control loop and is normally filtered and scaled prior to inputing at FB1 and
FB2 through separate input resistors to allow for different BWs.
6, 7 CS+, CS- The differential inputs for the current sense circuit. This circuit generates a DC feedback signal for the control loop as well as the
input to the CrCM circuit to determine the critical conduction operating point. CS± has a common mode range of -0.3V to 0.5V and
a differential input range of 0V to1.5V
8 REFIN The reference voltage input that sets the control loop reference. Normally connected to LPOUT or an external control reference.
9 LPOUT Output of the digital low-pass filter. The output ranges from 0V to 0.5V in proportion to the AC conduction angle. This output may be
used as is or manipulated (such as when used with an external light sensor or temperature monitor) and applied to REFIN to be used
as the reference for the control loop.
10
OC This is the input to the peak overcurrent comparator. The overcurrent comparator threshold is set at 600mV nominal. Peak OCP is
required for cycle-by-cycle protection. It also protects against low AC line conditions. OCP includes leading-edge-blanking (LEB), which
blocks the signal at the beginning of the OUT pulse for the duration of the blanking period, and also while the OUT pulse is low.
11, 12 FB2, FB1 FBx is the inverting input to the error amplifier (EAs). The current feedback signal is applied to EA1 and EA2. EA1 is the primary error
amplifier and is used for steady state operation. EA2 is the secondary control loop for operation during transients. Normally EA1 is
configured for low bandwidth operation, about 20Hz, to obtain power factor correction. EA2 is configured for higher BW to respond
to transients. Both error amplifiers are externally compensated to give the user complete flexibility.
13 DELADJ Sets delay before a new switching cycles starts. This adjustment allows the user to delay the next switching cycle until the switching
FET drain-source voltage reaches a minimum value to allow quasi-ZVS (Zero Voltage Switching) operation. A resistor to ground
programs the delay. Pulling DELADJ to VREF disables the CrCM oscillator.
14 VERR Output of the error amplifiers and the control voltage input to the inverting input of the PWM comparator. VERR requires an external
pull-up resistor to VREF.
15 RAMP This is the input for the sawtooth waveform for the PWM comparator. Using an RC from VREF, a sawtooth waveform is created for
use by the PWM. It is compared to the error amplifier output, VERR, to create the PWM control signal. The RAMP pin is shorted to
GND at the termination of the PWM signal.
16
LFB The inverting input to the uncommitted linear amplifier.
2
FN7981.2
March 20, 2013