feature

Ballast Control and Half-Bridge Driver Transformerless Lamp Power Sensing in One Integrated Circuit

Closed Loop Lamp Power Control

Closed loop preheat current control

Programmable warm-up time

Programmable Preheat Current

Lamp ignition detection

Programmable fire-to-dark time

0.5 to 5VDC dimming control input

Minimum and maximum lamp power adjustment

Programmable minimum frequency

Internal current sense blanking

Full light failure protection

brown protection

automatic restart

Micropower start

Zener clamp Vcc

Overheating protection

16-pin dip and SOIC package types

illustrate

Description: The IR21592 //IR21593 are complete dimming ballast controller and 600V half bridge driver all in one IC. The schysical includes phase control for trans \ 2formerless lamp power sensing and regulation which minimizes changes needed to adaptive non-scaled ballasts, external programmable characteristics of warm-up time and current, ignition-to-dim time, and a complete dimming interface Min Max settings provide high flexibility for ballast design engineers to protect against lamp failure, filament failure, thermal protection from overload or lamp failure during normal operation, as well as an automatic recovery function, which has been included in the design. The heart of the control IC is a voltage\2 controlled oscillator with an externally programmable minimum frequency. The IR21592IR21593 Available in both 16 PIN DIP and 16 PIN narrow body soil packages

Absolute Maximum Ratings

Absolute Maximum Ratings represent the lasting limits to which device damage may occur. The full voltage parameter is the absolute voltage referenced to COM, and all currents are defined as being positively charged into any lead. Thermal resistance and power dissipation ratings are measured with board mounted and still air conditions

Note 1: This IC contains a Zener clamp structure between chip VCC and COM, which has a nominal fault voltage of 15.6V (VCLAMP). Note that this supply pin should not be driven by a low impedance DC power supply greater than the diode clamp voltage specified in the Electrical Characteristics (VCLAMP section.

Recommended Operating Conditions

For proper operation, the equipment should be used under the recommended conditions.

Note 2: Sufficient current should be supplied to the VCC lead to maintain the internal 15.6V Zener clamp diode regulation voltage, VCLAMP, on this lead.

Note 3: The largest lead is a voltage controlled current source. For best weak interface current mirror performance, this current should be kept between 0 and 750 µA.

Electrical Characteristics

VCC=VBS=VBIAS=14V/-0.25V, VCS=0.5V, VSD=0.0V, RFMIN=40k, CVCO=10NF, VDIM=0.0V, RMAX=33k, RMIN=56k, VCPH=0.0V, CLO, HO=1000pF, TA=25oC unless otherwise specified

Phase control

To understand phase control, a simplified model uses the ballast output stage (Figure 1). The lamp and filament are replaced with resistors, and the lamp is inserted between the filament resistors (R1, R2, R3 and R4).

During warm-up and ignition (Figure 2), the circuit is a high-Q series LC with strong input current from +90 to -90 degrees of phase reversal of the input voltage at the resonant frequency. For operating frequencies slightly above resonance and higher, the phase is fixed at -90 degrees for preheat and ignition during this time. During dimming, the circuit is an L in series with a parallel R and C, with a weak phase inversion at high power and a strong phase inversion at low lamp power.

In the time domain (Figure 3), the input current is the voltage during warm-up and firing when moving -90 degrees from the input half-bridge, and firing when operating between 0 and -90 degrees. Zero phase shift corresponds to maximum power.

When calculating and plotting the phase of the lamp power (Figure 4), the result is a linear dimming curve, even to ultra-low light levels, the resistance of the lamp can change sequentially by orders of magnitude.

The IR21592/IR21593 undervoltage lockout is designed to keep ultra-low quiescent current less than 200uA while keeping the IC output drivers active on both the high and low side. Figure 5 shows the current from the ballast output stage (R1, C1, C2, D1 and D2) using the effective supply voltage IR21592/IR21593 to start.

The startup capacitor (C1) is charged by the current through the resistor (R1) minus the startup current drawn by the IC. Typically this resistor is chosen to provide 2 times the maximum start-up current on the low line to guarantee worst case start-up conditions. Once the capacitor voltage reaches the start-up threshold, and the voltage on pin VDC is above 5.1V (see brown protection), the IC turns on and the HO and LO begin to oscillate. This capacitor begins to discharge the IC operating current due to the increase (Figure 6).

During the discharge cycle, the rectified current flows from the charge pump to the upper capacitor to charge the device's minimum operating voltage and the charge pump and the internal 15.6V Zener clamp as the supply voltage. The start-up capacitor and snubber capacitor must be selected to satisfy worst-case IC conditions. A bootstrap diode (D3) and supply capacitor (C3) include the high-side driver circuit. Ensure that the high-side power supply pulses on the first pin HO, and the first pulse driver of the output comes from the LO pin. During UV exposure, the high-side and low-side driver outputs are low, pin VCO is internally pulled up to 5V, resetting the maximum startup frequency, and pin CPH is internally shorted to COM, resetting the warm-up time.

brown protection

In addition to the voltage on VCC above the start-up threshold pin VDC must also be above 5.1V, HO and LO start to oscillate. A voltage divider (R3, RVDC) from the rectified AC is connected to the line at pin VDC to measure the AC line input voltage of the rectified ballast and program on and off the line voltage. The filter capacitor (CVDC) also connected to pin VDC must be chosen low enough for ripple, the low turn-off threshold of 3V is not crossed under normal line conditions. This is due to the possibility of the lamp going out under low line conditions before the IC resets properly. If a brown output is present, the DC bus may drop to the minimum level required by the tank circuit to maintain the necessary lamp voltage. This detection will ensure that the DC bus drops too low and resets properly when the line returns and the IC goes into preheat mode. Preheat (PH) The IR21592/IR21593 enters preheat mode when VDC exceeds 5.1V when VCC exceeds the UVLO+ threshold. HO and LO start to oscillate at the maximum operating frequency with a 50% duty cycle, with an internally set dead time of 2us (IR21592) or 1 microsecond (IR21593). Pin CPH is linear with COM and an internal 1uA current source (Figure 7) for external charging of the timing capacitor on CPH.

The internal 1uA current source slowly discharges the external capacitance on pin VCO and the voltage starts to decrease at pin VCO. This reduces the frequency and, for operating frequencies above resonance, increases the load current. When a peak voltage is measured on pin CS, generated by a portion of the load current through an external sense resistor (RCS), exceeding the voltage level on pin IPH, an internal 60uA current source is connected to pin VCO and the capacitor is charged (Fig. 8). This forces an increase in frequency and a decrease in load current. When the voltage on pin CS drops below the voltage on pin IPH, the 60uA current supply is disconnected and the frequency is reduced again.

This feedback keeps the peak preheat current regulated to a user programmable pin setting using IPH during the preheat time. A resistor connected to the external internal current source pin IPH provides the peak preheat current. The warm-up time continues until the voltage on pin CPH exceeds 5 volts. Ignition (IGN) The voltage on pin CPH exceeds 5V when the IR21592/IR21593 enters ignition mode. The peak current regulation reference voltage is set on pin IPH with a user programmable disconnect and connected to a higher internal threshold of 1.6V (Figure 9).

The ignition ramp is then initiated as the capacitor on the pin VCO discharges linearly through the internal 1uA current source. This frequency reaches the resonant frequency stage of the high-Q ballast output, resulting in an increase in lamp voltage and load current (Figure 10). The frequency continues to drop until the lamp is lit or the current limit of the IR21592/IR21593 is reached. If the current limit is reached, the IR21592/IR21593 goes into failure mode. The 1.6 volt threshold and a sense resistor on the external current contact pin CS determine the maximum allowable peak ignition current (and therefore, the ballast's peak ignition voltage output stage. The peak ignition current must not exceed the maximum allowable current rating of the output stage MOSFETs or IGBTs, Also, the resonant inductor must not be at any time. To prevent ignition at low brightness settings, the ignition detection circuit measures the CS pin and compares it to the voltage on the IPH pin. During the ignition ramp up the IPH pin is higher than it is is 20% higher in preheat mode. When the CS pin exceeds this voltage, the voltage on the IPH pin decreases to VIPH preheat +10%, and then the ignition detection circuit activates (see Figure 10). When the lamp is ignited When the voltage is turned on, then the CS pin will be lower than the IPH pin and the IC goes into dark mode and the phase control loop is closed. In order for the ignition detection circuit to work properly to enter the dimming mode, the voltage on the CS pin must rise for the first time Above VIPH preheat +20% the ignition ramp of the start-up circuit, then below VIPH preheat +10%, the lamp will ignite.

Ignition to Dashboard Integrated Module (Ignition to Dashboard Integrated Module) The phase control loop is closed when the IR21592/IR21593 enters dimming mode to adjust the load current input pin size according to user control. To control changing the dim setting from maximum brightness to user setting (IGN-to-DIM time, Figure 11), when the IR21592/IR21593 enters dimming mode. The resistor on this pin DIM (RDIM) discharges the capacitor on pin CPH down to the user size setting. The resistor can choose a time constant that quickly minimizes the amount of flash visible on the lamp after ignition, or a long time constant that ramps the brightness smoothly down to the user setting. The ignition time should be too fast, but the loop reacts faster than the ionization causing the VCO to overshoot. This results in a frequency brightness frequency higher than the minimum, which can turn off the light. The capacitor on pin CPH serves multiple functions by setting the warm-up time, stroke post-fire rate (along with resistor RDIM), and, as a filter capacitor on the pin when dimmed to increase high frequency noise immunity and minimize number of components.

Dimming (DIM) In order to adjust the power of the lamp, the current in the reference phase and the output phase forces the VCO to turn the frequency in the correct direction, the function of the output stage is determined by the transfer, so that the error is forced to zero. An internal 15uA current source is connected to pin VCO in dimming mode (Figure 12) to discharge the VCO capacitor and reduce the locking frequency.

Once locked, the phase detector (PDET) outputs a short pulse to the open-drain PMOS through an internal resistor (RFB) each time a false pulse occurs (Figure 13). This action "pushes" the input of the integrator VCO to keep the output stage current in line with ref.

IR21592/IR21593 includes a dimming analog lamp power control interface. This size pin input requires a voltage of 0.5 to 5VDC, with 5V corresponding to the minimum phase shift (maximum lamp power). The voltage at the output dim interface is pin MIN, which is compared with the internal time capacitor (CT) to produce a frequency independent digital reference phase voltage (Figure 14).

The CT charging time from 1V to 5.1V determines the turn-on time of the output gate driver HO and the possible phase shift (negative dead time) of the LO corresponding to the -180 degree load current. The voltage on pin MIN is limited to 1V over the range of 0 to 90 degrees and 3V using the min and max pins. The minimum phase shift reference (maximum lamp power) of the external resistor in the pin MAX program corresponds to the pin size of 5V, and there is an external resistor MIN on the pin to set the maximum phase shift (minimum lamp power) corresponding to the pin adjustment of 0.5V. dark. Current Sensing During dimming, a current sensing circuit (Figure 15) detects possible overcurrents during hard switching (see the Faults section), as well as measures the zero-crossing load current of the total phase. To reject any switching noise that may occur in the turn-on position of the low-side MOSFET or IGBT, a digital current-sense blanking circuit causes the zero-crossing signal to disappear from low to "high" after 400ns of the sense comparator (Figure 16).

The internal blanking time reduces the dimming range slightly (Figure 16) phase shift (maximum lamp power) during minimum operation. The programming resistor on the external pin MAX must be selected so that the minimum phase shift is set by a safety margin during the blank time. One needs a series resistor (R1) to limit the amount when the voltage across the RCS is below -0.7V. Filter capacitors may be required for other possible reasons for the asynchronous noise source system present in the pin CS ballast.