Datasheet LT6559 (Analog Devices) - 10

LT6559
TYPICAL APPLICATIONS 3-Input Video MUX Cable Driver Using the LT6559 to Drive LCD Displays
The application on the fi rst page of this data sheet shows Driving a variety of XGA and UXGA LCD displays can be a low cost, 3-input video MUX cable driver. The scope a diffi cult problem because they are usually a capacitive photo below (Figure 4) displays the cable output of a load of over 300pF, and require fast settling. 30MHz square wave driving 150Ω. In this circuit the ac- The LT6559 is particularly well suited for driving these LCD tive amplifi er is loaded by the sum of RF and RG of each displays because it can drive large capacitive loads with a disabled amplifi er. Resistor values have been chosen to small series resistor at the output, minimizing settling time. keep the total back termination at 75Ω while maintaining As seen in Figure 6, at a gain of +3 with a 16.9Ω output a gain of 1 at the 75Ω load. The switching time between series resistor and a 330pF load, the LT6559 is capable any two channels is approximately 32ns when both enable of settling to 0.1% in 30ns for a 6V step. pins are driven (Figure 5). When building the board, care was taken to minimize trace lengths at the inverting inputs. The ground plane was also pulled a few millimeters away from RF and RG on both sides of the board to minimize stray capacitance. EN A EN B OUTPUT 200mV/DIV OUTPUT 6559 F04 6559 F05 R V 20ns/DIV L = 150Ω 5ns/DIV S = ±5 R V F = RG = 301Ω INA = VINB = 2VP-P f = 10MHz at 3.58MHz
Figure 4. Square Wave Response Figure 5. 3-Input Video MUX Switching Response (AV = 2)
VIN VOUT 6559 F06 20ns/DIV VS = ±5 RG = 150Ω CL = 330pF RF = 301Ω RS = 16.9Ω
Figure 6. Large-Signal Pulse Response
6559f 10