IR2167 datasheet(16/30 Pages) IRF

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IR2167(S)

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is available over all ballast operating conditions. Bootstrap

diode (DBS) and supply capacitor (CBS) 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

HO, the first pulse from the output drivers comes from the

LO pin.

The Preheat mode oscillation frequency of the half-bridge

output is determined by the parallel combination of RPH and

RT with the values of CT, RDT and an internal circuit as

shown in Figure 3. Note that at the onset of Preheat mode

the initial startup frequency is much higher than the preheat

frequency. The half-bridge output frequency then ramps

down from this initial start-up frequency to the Preheat mode

frequency. This is to ensure that the instantaneous voltage

across the lamp during the first few cycles of operation does

not exceed the strike potential of the lamp

Ignition Mode

When the CPH pin charges up to 4.0V, ignition mode be-

gins. At this time, the output of COMP2 (figure 3) goes low,

4.0V

5.1V

9.5V

3.0uA

2.0V

CT = IRT

4.0V

2.0V

CPH

RPH

RUN

R2 Q

QUICK

RESTART

LOGIC

RAMP

RUN

Fault signal

COMP1

COMP2

Figure 3: Oscillator section block diagram with external component connection

M1 turns off and CRAMP begins to charge. CRAMP deter-

mines the time it takes for the oscillator to ramp down from

the Preheat frequency to the Ignition Mode frequency. Once

the voltage on the RPH lead reaches 2.0V, external resistor

RPH has no effect on the frequency that is now determined

by external components RT, CT and RDT. This is the mini-

mum frequency. By this time, the oscillator will have ramped

down toward the resonance of the load circuit causing the

lamp to ignite.

Run Mode

When the voltage on the CPH pin reaches 5.1V, the IC en-

ters Run mode. At this time, the output of COMP1 (figure 3)

goes high which turns M2 on and pulls the RUN pin to COM.

The frequency is now controlled by external components RT,

RRUN, CT and RDT. In certain cases it is necessary to have

the run frequency higher than the ignition frequency to con-

trol the power used by the load. Figure 4 shows the ballast

control sequence explained in the previous paragraphs

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