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參數(shù)資料
| 型號： | TPS68000DBTRG4 |
| 廠商： | TEXAS INSTRUMENTS INC |
| 元件分類： | 穩(wěn)壓器 |
| 英文描述： | FLUORESCENT LIGHT CONTROLLER, 100 kHz SWITCHING FREQ-MAX, PDSO30 |
| 封裝： | GREEN, PLASTIC, TSSOP-30 |
| 文件頁數(shù)： | 6/25頁 |
| 文件大小： | 981K |
| 代理商： | TPS68000DBTRG4 |
www.ti.com
Oscillator
Dimming
Startup
SLVS524A – OCTOBER 2005 – REVISED FEBRUARY 2006
DETAILED DESCRIPTION (continued)
For additional protection there is a standalone comparator implemented. It can be used to monitor any voltage in
the system. The switching threshold is set to the VREF voltage.
. This comparator monitors a voltage at its input and compares it with the internal reference voltage. As soon as
the input voltage of the comparator exceeds the reference voltage the comparator asserts FAULT at its output.
Negative voltages can be applied at that pin but there is no rectification. Since the input of the overcurrent
comparator is directly accessible at a pin it can be connected to any part of the circuit. It must not necessarily
use the shunt resistor used for current regulation. Monitoring the current in the secondary winding or any other
DC voltage in the system may be a desired approach as well.
Finally the device has an internal temperature sensor to monitor the IC temperature. If the temperature gets too
high FAULT is asserted as well. For detailed values for threshold and hysteresis of the thermal protection please
check the electrical characteristics table.
The device is operating at a fixed frequency which is generated by a built in PLL circuit. The frequency is
programmed with a resistor at SET. It also can be synchronized to an external frequency at SYNC. When
synchronizing to an external clock two modes are possible. One is to synchronize directly to the external clock,
the other is to synchronizeto the external clock but phase shifted. This helps to minimize the RMS input current
of the complete power converter application in a multi controller topology. This phase shift is programmed with a
DC voltage of 0 V to 2 V at PH for a phase shift of 0
° to 180°.
To dimm the lamp, two basic methods of dimming are supported. The first is to control the lamp current directly,
called analog dimming. The second is to turn the lamp on and off at a low frequency with a certain duty cycle,
called burst dimming. Analog dimming, is done by just providing a DC voltage at ABR. The lamp current will be
regulated propotional to that voltage. The maximum lamp current in burst dimming is also programmed with this
voltage at ABR.
Turning the lamp on and off, burst dimming, needs some more information. A low frequency must be generated
and duty cycle information for the on time needs to be provided. The simplest burst dimming mode, independent
burst dimming, is to program the low frequency with an external capacitor at BF. Applying a DC voltage at BBR
sets the duty cycle of the burst pulse. The burst duty cycle will be programmed proportional to the DC voltage at
BBR.
If the burst dimming frequency and duty cycle must be synchronized to an external PWM signal this external
signal can be connected to BC. The bursts follow the PWM signal directly. A PWM signal detected at BC has
priority to any internally generated burst signal. To force the device to take the BC PWM signal BBR can be tied
high (V5).
To minimize RMS input current in a multiple controller application the burst signal can be phase shifted to the
external PWM connected to BC, which is called Distributed Dimming
. Frequency and duty cycle stay the same.
The phase shift information is derived from the voltage at PH. Voltages of 0 V to 2 V at PH generate burst phase
shifts of 0
° to 360°. For this mode of operation the internal low frequency oscillator is used. It is operated as a
PLL synchronized to the PWM frequency at BC and its center frequency has to be programmed at BF. The
compensation of the low frequency PLL is done with and R - C network connected at BBR.
When the device is enabled or the device is powered up with EN tied high, the device enters lamp strike mode.
In this mode no dimming and synchronization is possible. During the strike procedure the lamp current which
should flow when the lamp has turned on is programmed at ABR.
The device starts operating at double the programmed operating frequency and sweeps down to half of the
nominal frequency. During this sweep it can cross the self resonance frequency of the system with its maximum
voltage gain. As soon as the lamp current has reached its programmed value the device stops sweeping and
switches to the nominal operating frequency. The device will continue to regulate the lamp current and all other
control features like synchronization and burst dimming are enabled and will be used. If during this sweep the
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