ISL59442EVAL1 Evaluation Board User’s Guide ® Application Note April 19, 2005 AN1185.0 Introduction High Frequency Layout Considerations The ISL59442EVAL1 evaluation board contains all the circuitry needed to characterize critical performance parameters of the ISL59442 single 4:1 MUX-amplifier, over a variety of applications. At frequencies of 500MHz and higher, circuit board layout may limit performance. The following layout guidelines are implemented on the evaluation board: The ISL59442 is a single-output 4:1 MUX-amp. The output amplifier unity-gain bandwidth is 1GHz. The device contains logic inputs for channel selection (S0, S1), and a three-state output control (HIZ) for individual selection of MUX amps that share a common video output line. The evaluation board circuit and layout is optimized for either 50Ω or 75Ω terminations, and implements a basic single 4:1 video MUX-amp. The board is supplied with 75Ω input signal terminations and a 75Ω back-termination resistor on each of the 3 outputs, making it suitable for driving video cable. The user has the option of replacing the 75Ω resistors with 50Ω resistors for other applications. The control lines contain 50Ω resistors to match the 50Ω output impedance of high speed pulse generators. Control line termination resistors are recommended for rise and fall times under 10ns to minimize unwanted transients. If DC is used for the control logic, the resistors may be removed; or the applied DC voltage can be reduced to 2.5V to reduce the dissipation in the termination resistor. The layout contains component options to include an output series resistor (RS) followed by a parallel resistor (RL) capacitor (CL) network to ground. This option allows the user to select several different output configurations. Examples are shown in Figures 2A, 2B, and 2C. The evaluation board is supplied with the 75Ω back termination resistors shown in Figure 2C. • Signal I/O lines are the same lengths and widths to match propagation delay and trace parasitics. • No series connected vias are used in signal I/O lines, as they can add unwanted inductance. • Signal trace lengths are minimized to reduce transmission line effects and the need for strip-line tuning of the signal traces. • High frequency decoupling caps are placed as close to the device power supply pin as possible - without series vias between the capacitor and the device pin. Power Sequencing Proper power supply sequencing is -V first, then +V. In addition, the +V and -V supply pin voltage rate-of-rise must be limited to ±1V/µs or less. The evaluation board contains parallel-connected low VON Schottky diodes on each supply terminal to minimize the risk of latch up due to incorrect sequencing. In addition, extra 10µF decoupling capacitors are added to each supply to aid in reducing the applied voltage rate-of-rise. Reference Documents • ISL59442 Data Sheet, FN7452 EN0 S0 EN1 IN0 IN1 Amplifier Performance and Output Configurations DECODE EN2 S1 The ISL59442 output amplifier is sensitive to capacitance at the output. For best AC performance, a series output resistor is required to reduce excessive gain peaking, particularly when long PB board traces are used. The output amplifier is ideally suited for driving high impedance high speed selectable-gain buffers when gain compensation is needed. GBW decreases slightly at the lower output load impedances typical of back-terminated cable driving applications. Reference data sheets for additional performance data. 1 EN3 IN2 OUT IN3 HIZ FIGURE 1. ISL59442 FUNCTIONAL BLOCK DIAGRAM CAUTION: These devices are sensitive to electrostatic discharge; follow proper IC Handling Procedures. 1-888-INTERSIL or 1-888-352-6832 | Intersil (and design) is a registered trademark of Intersil Americas Inc. Copyright Intersil Americas Inc. 2005. All Rights Reserved All other trademarks mentioned are the property of their respective owners. Application Note 1185 TABLE 1. LOGIC TABLE ISL59442 VIN 50Ω OR 75Ω S0 S1 HIZ OUT 0 0 0 IN0 1 0 0 IN1 0 1 0 IN2 1 1 0 IN3 - - 1 High Z Cb1 ~0.5pF TEST EQUIPMENT ISL59442 RS, 0Ω RS VIN *Cb2 ~3pF * Cb1, Cb2 are approximate PCB trace capacitances. 50Ω OR 75Ω FIGURE 2B. TEST CIRCUIT FOR 50Ω OR 75Ω TERMINATIONS ISL59442 50Ω OR 75Ω ~0.5pF 50Ω OR 75Ω * Cb1 is approximate PCB trace capacitance. FIGURE 2A. TEST CIRCUIT WITH OPTIMAL OUTPUT LOAD VIN 475Ω Cb1 RL 50Ω OR 75Ω RL 500Ω RS 50Ω OR 75Ω Cb1 ~0.5pF TEST EQUIPMENT 50Ω OR 75Ω * Cb1 is approximate PCB trace capacitance. FIGURE 2C. BACK-TERMINATED TEST CIRCUIT FOR CABLE APPLICATION ISL59442EVAL1 Top View 2 AN1185.0 April 19, 2005 Application Note 1185 ISL59442EVAL1 Schematic Diagram ISL59442 IN0 R2 75Ω IN1 R10 75Ω 1 IN0 V+ 14 2 GND S0 13 3 IN1 S1 12 HIZ 11 4 GND IN2 OUT 10 5 IN2 JS0 S0 JS1 R19 - 49.9Ω S1 JHIZ R18 - 49.9Ω HIZ R12 - 49.9Ω OUT RS - 75Ω R11 75Ω NIC 9 6 GND V- 8 7 IN3 IN3 C10 R21 R1 75Ω D1 C2 C1 C3 10µF 0.1µF 10nF C7 1nF + D2 GND V- + C5 C4 C6 10µF 0.1µF 10nF C8 1nF V+ ISL59442EVAL1 Components Parts List DEVICE # DESCRIPTION COMMENTS C7, C8 CAP, SMD, 0603, 1000pF, 25V, 10%, X7R Power Supply Decoupling C1, C4 CAP, SMD, 0603, 0.01µF, 25V, 10%, X7R Power Supply Decoupling C2, C5 CAP, SMD, 0603, 0.1µF, 25V, 10%, X7R Power Supply Decoupling C3, C6 CAP, SMD, 0805, 10µF, 6.3V, 10%, X5R Power Supply Decoupling D1, D2 Diode-Schottky, 2 Pin, 45V, 7.5A MBR0550T (Motorola) Reverse Polarity Protection Resistor, SMD, 0603, 75Ω, 1/10W, 1% Signal Input/output Termination Resistor, SMD, 0603, 49.9Ω, 1/16W, 1% Logic Input Termination C10 Resistor, SMD, 0603 Optional, not populated R21 Resistor, SMD, 0603 Optional, not populated U1 ISL59442 - 1GHz Multiplexing Amplifier, 14P, QSOP Device Under Test R1, R2, R10, R11, RS R12, R18, R19 Intersil Corporation reserves the right to make changes in circuit design, software and/or specifications at any time without notice. Accordingly, the reader is cautioned to verify that the Application Note or Technical Brief is current before proceeding. For information regarding Intersil Corporation and its products, see www.intersil.com 3 AN1185.0 April 19, 2005