DS3991
Low-Cost CCFL Controller
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Pin Description
PIN NAME I/O FUNCTION
1 SLOPE I
BRIGHT Slope Select. This digital input determines the slope of the BRIGHT input when
an analog DC voltage is used to control lamp brightness (PWM_EN = 0).
SLOPE = 0: positive slope (0V = minimum brightness, 3.3V = 100% brightness)
SLOPE = 1: negative slope (0V = 100% brightness, 3.3V = minimum brightness)
2, 3, 4 VCC Connect to Voltage Supply. These pins should be connected to the voltage supply pin, VCC.
5 LOSC O
Lamp Oscillator Resistor Adjust. A resistor (R
LOSC
) to ground on this pin sets the frequency
of the lamp oscillator (F
LOSC
). (R
LOSC
x F
LOSC
= 4.0E9).
6
POSC/
PWM
O/I
Burst-Dimming PWM Oscillator Resistor Adjust/PWM Digital Input. If PWM_EN = 0, a resistor
(R
POSC
) to ground on this pin sets the frequency (F
POSC
) of the burst-dimming PWM
oscillator (R
POSC
x F
POSC
= 4.0E6). If PWM_EN =1, a digital 80Hz to 300Hz PWM signal at
this input controls the lamp brightness.
7 BRIGHT I
Lamp-Brightness Control. If PWM_EN = 0, a 0V to 3.3V analog DC voltage at this input
controls the brightness of the lamp.
8 PWM_EN I
PWM Lamp-Brightness Control Enable. This digital input determines whether the BRIGHT or
POSC/PWM input is used to control lamp brightness.
PWM_EN = 0 = PWM disabled (analog DC voltage applied at the BRIGHT input)
PWM_EN = 1 = PWM enabled (digital PWM signal applied at the POSC/PWM input)
9 GA O MOSFET Gate Drive A. Drives a logic-level power MOSFET.
10 GB O MOSFET Gate Drive B. Drives a logic-level power MOSFET.
11 LCM I
Lamp Current Monitor Input. Lamp current is monitored by a resistor placed in series with
the low-voltage side of the lamp.
12 OVD I
Overvoltage Detection Input. Lamp voltage is monitored by a capacitor divider placed on
the high-voltage side of the lamp.
13 GND Signal Ground
14 VCC Voltage Supply, 4.5V to 5.5V
15 SVMH I
Supply Voltage Monitor High. The DC inverter-supply voltage is monitored by an external
resistor divider. The resistor-divider should be set such that it provides 2V at this pin for the
maximum allowable range of the DC inverter supply. Pulling this input above 2V turns the
lamps off and resets the controller. Connect to GND if not used.
16 SVML I
Supply Voltage Monitor Low. The DC inverter-supply voltage is monitored by an external
resistor divider. The resistor-divider should be set such that it provides 2V at this pin for the
minimum allowable range of the DC inverter supply. Pulling this input below 2V turns the
lamps off and resets the controller. Connect to VCC if not used.
