IRS21571DSPBF International Rectifier, IRS21571DSPBF Datasheet - Page 20

• Manufacturer Part Number: IRS21571DSPBF
• Description: IC BALLAST CTRL 600V 16-SOIC
• Manufacturer: International Rectifier
• Type: Ballast Controllerr

Specifications of IRS21571DSPBF

• Frequency: 43.7 ~ 48.3 kHz
• Current - Supply: 10mA
• Current - Output: 180mA
• Voltage - Supply: 11.5 V ~ 15.6 V
• Operating Temperature: -40°C ~ 125°C
• Package / Case: 16-SOIC (0.154", 3.90mm Width)
• Package: 16-lead SOIC Narrow
• Circuit: Fluorescent Ballast IC
• Offset Voltage (v): 600
• Output Source Current Min (ma): 180
• Output Sink Current Min (ma): 260
• Pbf: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

www.irf.com
Sensing The DC Bus Voltage
The first of these protection pins senses the voltage on the DC bus by means of an external resistor divider and
an internal comparator with hysterisis.
When power is first supplied to the IC at system startup, 3 conditions are required before oscillation is initiated: 1.)
the voltage on the VCC pin must exceed the rising undervoltage lockout threshold (12.5V), 2.) the voltage at the
VDC pin must exceed 5.1V, and 3.) the voltage on the SD pin must be below approximately 1.85V. If a low dc bus
condition occurs during normal operation, or if power to the ballast is shut off, the dc bus will collapse prior to the
VCC of the chip (assuming the VCC is derived from a charge pump off of the output of the half-bridge). In this
case, the voltage on the VDC pin will shut the oscillator off, thereby protecting the power transistors from
potentially hazardous hard switching. Approximately 2V of hysterisis has been designed into the internal
comparator sensing the VDC pin, in order to account for variations in the dc bus voltage under varying load
conditions. When the dc bus recovers, the chip restarts from the beginning of the control sequence, as shown in
timing diagram Figure 11 below.
Lamp Presence Detection and Automatic Restart
The second protection pin, SD, is used for both unlatched shutdown and automatic restart functions. The SD pin
would normally be connected to an external circuit which senses the presence of the lamp (or lamps). A example
circuit for a single lamp is shown in Figure 12.
VDC
CT
CPH
LO
HO-VS
Figure 11: VDC pin fault and auto restart
5
3
15
15
4
8
RUN mode
20
Low VDC
Restart
© 2008 International Rectifier
IRS21571D