IR21571S International Rectifier, IR21571S Datasheet - Page 9

• Manufacturer Part Number: IR21571S
• Description: IC BALLAST CONTROL 16-SOIC
• Manufacturer: International Rectifier
• Type: Ballast Controllerr

Specifications of IR21571S

• Frequency: 45.5 ~ 50.5 kHz
• Current - Supply: 5.5mA
• Current - Output: 500mA
• Voltage - Supply: 11.4 V ~ 15.6 V
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 16-SOIC (3.9mm Width)
• Package: 16-lead SOIC Narrow
• Circuit: Fluorescent Ballast IC
• Offset Voltage (v): 625
• Output Source Current Min (ma): 250
• Output Sink Current Min (ma): 400
• Vcc Range (v): 10-25V with UVLO
• Output Voltage Min (v): 10
• Output Voltage Max (v): 25
• Special Ic: Fully Integrated
• Pbf: PbF Option Available
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: *IR21571S

The IR21571 uses the following control sequence
(Figure 3) to drive rapid start fluorescent lamps.
www.irf.com
The control sequence used in the IR21571 allows
the Run Mode operating frequency of the ballast to
be higher than the ignition frequency (i.e., fstart >
fph > frun > fign). This control sequence is
recommended for lamp types where the ignition
frequency is too close to the run frequency to ensure
proper lamp striking for all production resonant LC
component tolerances (please note that it is possible
to use the IR21571 in systems where fstart > fph >
fign > frun, simply by leaving the RUN lead open).
Six leads in the IC are used to control the Startup,
Preheat, Ignition Ramp, and Run modes of
operation, and to allow ballast and lamp engineers
the flexibility to optimize their designs for virtually
any lamp type.
V
V
V
f
f
f
f
The Control Sequence & Timing
Start
PH
Run
min
CPH
RPH
RUN
5V
2V
2V
Figure 3: IR21571 control sequence
Component Selection
Preheat mode
Ignition
Ramp
mode
Run mode
t
The heart of this controller is an oscillator which
resembles those found in many popular PWM voltage
regulator ICs. In its simplest form, this oscillator
consists of a timing resistor and capacitor connected
to ground. The voltage across the timing capacitor
CT is a sawtooth, where the rising portion of the ramp
is determined by the current in the R
falling portion of the ramp is determined by an external
deadtime resistor R
illustrates the relationship between the oscillator
capacitor waveform and the gate driver outputs.
The deadtime can be programmed by means of the
external R
capacitor values, using the graph shown in Figure 5.
The R
where the voltage is regulated to be approximately
2.0V. In order to maintain proper linearity between
the R
current, the value of the R
kept between 50µA and 500µA. The R
also be used as a feedback point for closed loop
control.
T
T
lead current and the C
input is a voltage-controlled current source,
DT
IR21571 (S) & (PbF)
resistor, given a certain range of CT
DT
. The oscillograph in Figure 4
Figure 4
T
lead current should be
T
capacitor charging
T
lead, and the
T
lead can
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