IR2159S datasheet(15/25 Pages) IRF

15 / 25 page

IR21592/IR21593(S)

www.irf.com

-90.0

-85.0

-80.0

-75.0

-70.0

-65.0

-60.0

Lamp Pow er [Watts]

Figure 4, Lamp power vs. phase of output stage.

Under-voltage Lock-Out (UVLO)

The IR21592/IR21593 undervoltage lock-out is

designed to maintain an ultra low quiescent

current of less than 200uA, while guaranteeing

the IC is fully functional before the high and low

side output drivers are activated. Figure 5 shows

an efficient supply voltage using the start-up

current of the IR21592/IR21593 together with a

charge pump from the ballast output stage (R1,

C1, C2, D1 and D2).

COM

VCC

Rectified

AC Line

Half-Bridge

Output

RVDC

BUS (+)

RCS

BUS (-)

VDC

CVDC

DISCHARGE

TIME

INTERNAL

CLAMP VOLTAGE

VHYST

UVLO+

UVLO-

CHARGE PUMP

OUTPUT

R1 & C1 TIME

CONSTANT

DISCHARGE

Figure 6, Start-up capacitor (C1) voltage.

During the discharge cycle, the rectified current

from the charge pump charges the capacitor above

the minimum operating voltage of the device and

the charge pump and internal 15.6V zener clamp

of the IC take over as the supply voltage. The

start-up capacitor and snubber capacitor must be

selected such that worst case IC conditions are

satisfied. A bootstrap diode (D3) and supply

capacitor (C3) comprise the supply voltage for

the high side driver circuitry. To guarantee that

the high-side supply is charged up before the first

pulse on pin HO, the first pulse from the output

drivers comes from the LO pin. During UVLO,

the high and low side driver outputs are low, pin

VCO is pulled-up internally to 5V resetting the

starting frequency to the maximum, and pin CPH

is short-circuited internally to COM resetting the

preheat time.

Figure 5, Typical application of start-up circuitry.

The start-up capacitor (C1) is charged by current

through resistor (R1) minus the start-up current

drawn by the IC. This resistor is typically chosen

to provide 2X the maximum start-up current at

low line to guarantee start-up under the worst case

condition. Once the capacitor voltage reaches the

start-up threshold, and, the voltage on pin VDC is

above 5.1V (see Brown-out Protection), the IC

turns on and HO and LO begin to oscillate. The

capacitor begins to discharge due to the increase

in IC operating current (Figure 6).

IR2159S Datasheet(PDF) 15 Page - International Rectifier

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