Datasheet

5
UCC2305
UCC3305
DIVPAUSE: The QOUT and QOUT outputs can be used
to switch lamp polarity in an AC ballast. It is important to
stop polarity switching when the lamp is being lit, so that
the arc across the electrodes can form in the correct
place. Pulling high on DIVPAUSE stops the internal di
-
vider which generates the QOUT and QOUT
signals, and
thereby freezes the QOUT and QOUT
signals.
To stop the divider when the lamp is being lit and start af
-
ter the lamp has lit, connect a resistor from NOTON to
DIVPAUSE and a capacitor from DIVPAUSE to GND.
FLTC: The voltage on VOUTSENSE is proportional to
lamp voltage. If that voltage is too high or too low, the
lamp is either open, shorted, or not yet running. During
normal operation, there is a capacitor connected to
FLTC, and this capacitor is discharged to 0V by a current
source inside the UCC3305.
The UCC3305 monitors the voltage on VOUTSENSE
and compares it to an internal 83mV lower threshold and
a 2V upper threshold. If the voltage is outside this win
-
dow, then the IC will pull up on FLTC with a current of ap-
proximately 250nA. If the fault remains long enough to
charge the external FLTC capacitor over 5V, the control-
ler declares a catastrophic fault and shuts the IC down.
The IC will stay shut down until power is removed from
BOOST.
If the fault clears before the FLTC capacitor reaches 5V,
the capacitor discharges down to 0V. This discharge cur-
rent is approximately 50nA, representing a five times lon-
ger discharge rate than charge rate.
FLT: If the voltage on the FLTC pin exceeds 5V, indicat
-
ing a severe fault, then a latch in the UCC3305 sets and
PWM drive is halted. In addition, the FLT output goes
high to VCC, indicating a serious system fault.
FB: Differences between commanded lamp power and
desired lamp power are amplified by an error amplifier.
This amplifier senses the difference between the voltage
at FB and 2.5V, and drives COMP with an amplified error
voltage.
GND: Ground for all functions is through this pin.
ISENSEIN: The power regulating algorithm in the
UCC3305 HID Controller computes a function of lamp
current and lamp voltage and commands the appropriate
battery current to keep lamp power constant. This appro
-
priate battery current is sensed by a connection from
I-SENSEIN to a current sense resistor. This current
sensed pulse width modulation scheme is often referred
to as current mode control.
In addition to this current regulation, the UCC3305 con
-
tains peak input current limiting. This limiting is set to
0.2V across the ISENSEIN resistor during normal opera
-
tion and 0.4V during starting. The transition from starting
to normal operation is accomplished by the rise of the
WARMUPC capacitor.
Current mode control has an advantage over voltage
mode control in that a current mode loop is easier to
compensate. Current mode control has a disadvantage
compared to voltage mode control in that the loop can
enter into chaotic oscillations at high duty cycles. These
chaotic oscillations can be prevented using slope com
-
pensation. The UCC3305 contains internal slope com
-
pensation in the form of a current proportional to OSC
voltage on ISENSEIN. This current combined with an ex
-
ternal resistor from ISENSEIN to the current sense resis
-
tor creates a voltage drop proportional to OSC voltage,
which gives slope compensation.
ISET: Many functions inside the UCC3305 require pre
-
cise currents to give well controlled performance. These
controlled currents are programmed by a resistor from
ISET to GND. A resistor of 100k programs the IC to nor
-
mal operating current. Lower resistor values increase the
internal currents. Some of the functions which are influ-
enced by this resistor are WARMUPC charging and dis-
charging, SLOPEC charging and discharging, FLTC
charging and discharging, and error amplifier bandwidth
LOADISENSE: Just as ISENSEIN is normally connected
to a current sense resistor which monitors battery cur-
rent, LOADISENSE is normally connected to a resistor
which monitors lamp current. Lamp current is then regu-
lated by the controller such that the correct lamp power is
supplied at every lamp temperature, in conjunction with
the lamp voltage sensed by VOUTSENSE.
LPOWER: LOADISENSE directly drives one input of an
op amp in the UCC3305. This amplifier amplifies the dif
-
ference between the desired load current and the actual
load current, and generates an output signal on
LPOWER which feeds the error amplifier.
NOTON: While the lamp is in a fault condition, such as
excessively high or low lamp voltage, NOTON is pulled
high to VCC, indicating that the arc is not yet correct.
When the voltage on VOUTSENSE is within the 83mV to
2V window, NOTON is pulled low.
OSC: The fixed frequency PWM in the UCC3305 oper
-
ates at the frequency programmed by the OSC pin.
Typically, a a 200pF capacitor from OSC to GND pro
-
grams the PWM frequency at 100kHz. In addition, this
programs the charge pump at 50kHz and the QOUT
and
QOUT signals at 192Hz. The actual oscillator frequency
is a function of both the capacitor from OSC to GND and
the resistor from ISET to GND.
PUMPOUT: Although the UCC3305 is powered from the
VCC input, most functions of the device operate from a
supply voltage of approximately 10V connected to
BOOST. In normal operation, this 10V supply is gener
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PIN DESCRIPTIONS (cont.)