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UCC2305DW Datasheet(PDF) 6 Page - Texas Instruments |
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UCC2305DW Datasheet(HTML) 6 Page - Texas Instruments |
6 / 14 page 6 UCC2305 UCC3305 ated by a voltage doubler using the PUMPOUT pin as an AC signal and external diodes as switches. PUMP-OUT is a square wave which swings from VCC to GND at half of the OSC frequency. PWMOUT: The output of the pulse width modulator is a command signal to a power MOSFET switch. This sig- nal appears on PWMOUT. In normal systems, PWM-OUT can be directly connected to the gate of an N-channel power MOSFET such as the IRF540. If the lead between the UCC3305 and the MOSFET is longer than a few cm, a 10 ohm resistor from PWMOUT to gate may be required to dampen overshoot and under- shoot. QOUT: The UCC3305 is immediately configured for DC HID lamps. To operate with AC HID lamps, it is neces- sary to add a power H-bridge which will toggle lamp voltage. A practical switching frequency for this toggle function is the OSC frequency divided by 512, or 192Hz for a 100kHz oscillator. The QOUT pin is a logic output which toggles at the OSC frequency divided by 512, 180 degrees out of phase with the QOUT pin. QOUT: The QOUT pin is a logic output which toggles at the OSC frequency divided by 512, 180 degrees out of phase with the QOUT pin. SLOPEC: To track lamp warm-up and cool down, two capacitors connected to the UCC3305 charge and dis- charge. One is connected to SLOPEC. The other is con- nected to WARMUPC. The capacitor connected to SLOPEC charges up to 5V with a rate controlled by the resistor from ISET to GND. With a nominal 100k ISET resistor the charging current into SLOPEC is equivalent to the current from a 50Meg resistor to 5V. When power is removed from VCC, SLOPEC dis- charges at a constant current, nominally 100nA. VCC: VCC is the main supply input to the UCC3305. Many functions in the UCC3305 are powered by VCC, while others are powered by BOOST. VCC should be clamped to 6.8V by an external zener diode and kept as close to 6.8V as practical with a low value resistor to the input supply. VOUT-SENSE: The VOUTSENSE input is used to sense lamp voltage, commonly through a 120:1 voltage divider. For a normal, running HID lamp, the voltage across the lamp is between 60V and 110V. It takes higher than 300V to break down the lamp, and it is de- sirable to limit the voltage on the starter input to 600V maximum. A lamp voltage less than 10V is indicative of a shorted lamp. The UCC3305 regulates lamp power by commanding the correct lamp current for a given lamp voltage. In ad- dition, a comparator in the UCC3305 terminates a PWM cycle if VOUTSENSE reaches 5V, corresponding to 600V on the lamp. This regulates lamp voltage at 600V when the lamp is not lit. Comparators in the UCC3305 also compare VOUTSENSE to 83mV corresponding to 10V lamp voltage and 2V, corresponding to a 240V lamp voltage. When the VOUTSENSE voltage is out- side this window, the lamp is either not lit, shorted, or open. WARMUPC: In addition to the capacitor from SLOPEC to GND, lamp temperature is estimated by the voltage on a capacitor from WARMUPC to GND. This capacitor is charged by a 200nA current source to 4.2V and by a 100nA current source from 4.2V to 10V when the lamp is on, and discharged by 39nA current sink to 2.5V and 11nA current sink to GND when the lamp is off. WARMUPV: The voltage on WARMUPC is used to modulate the signal fed to the error amplifier through FB. However, the impedance on WARMUPC is too high to be directly used. The UCC3305 contains a buffer am- plifier which buffers the voltage on WARMUPC and pro- cesses it to WARMUPV, making a signal appropriate for driving FB. PIN DESCRIPTIONS (cont.) APPLICATIONS INFORMATION Typical Application This circuit shows the UCC3305 HID Lamp Controller IC in a flyback converter. The output of the converter is reg- ulated at constant power, so that lamp intensity is rela- tively constant regardless of small lamp manufacturing variations. Full Bridge Output Stage The output of the flyback converter is directed to the AC lamp through a full bridge inverter. The full bridge is switched at a low frequency (typically 195Hz), so that the average lamp voltage is zero. The low frequency switch- ing is derived from the PWM oscillator. It is desirable to switch lamp polarity when running, but switching lamp polarity can interfere with clean starting. The UCC3305 has a logic output called NOTON which is high when the lamp is not running (Not On) and low when the lamp is running. This output is connected to the DIVPAUSE input so that the low frequency switching stops until the lamp is fully lit. The UCC3305 HID Controller IC has two low frequency outputs, QOUT and QOUT. These outputs are capable of driving low-side MOSFETs directly at 195Hz, but high-side MOSFETs require a level-shifted drive. This |
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