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19-1143; Rev 0; 10/96
KIT ATION EVALU E AILABL AV
Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers
____________________________Features
o High Speed: 250MHz Small-Signal -3dB Bandwidth 135MHz Full-Power -3dB Bandwidth o 70MHz 0.1dB Gain Flatness o 1250V/s Slew Rate o 12ns to 0.1% Settling Time o 0.03/0.06% Differential Phase/Gain Error o 2pF Input Capacitance o 3ns Channel-Switching Time o 120mVp-p Channel-Switching Transient o Three-State Output Allows Large Switch Arrays o Directly Drives 50 or 75 Back-Terminated Cables
_______________General Description
The MAX498/MAX499 are high-speed, quad/triple, single-pole/double-throw video switches with on-board closed-loop buffer amplifiers. The buffer amplifiers feature +6dB gain (AVCL = 2V/V), 250MHz -3dB bandwidth, 70MHz 0.1dB gain flatness, and 1250V/s slew rate. Fast switching time (3ns) and fast settling time (12ns for a 4V step) make these devices excellent choices for a wide variety of video applications. The low differential gain/phase errors (0.03%/0.06) and wide bandwidth make them ideal for both composite-video and RGB applications. The amplifiers are capable of delivering 2.5V into back-terminated 50 or 75 cables, and they deliver 2V to a 75 load, allowing multiple cables to be driven from a single output. For implementation of large switch arrays, a low-power disable mode places the amplifier outputs in a highimpedance state. Channel selection and output enable/disable are controlled by four TTL/CMOScompatible logic inputs. Each video input is isolated by an AC-ground pin, which minimizes channel-to-channel capacitance and reduces crosstalk to 90dB at 10MHz. The four-channel MAX498 dissipates 390mW (typical) from 5VDC power supplies with all output buffers enabled. Power consumption is reduced to 130mW with all buffers disabled. The corresponding dissipation for the three-channel MAX499 is 300mW enabled and 100mW disabled.
MAX498/MAX499
______________Ordering Information
PART MAX498CWI MAX499CWG TEMP. RANGE 0C to +70C 0C to +70C PIN-PACKAGE 28 SO 24 SO
________________________Applications
Video Switching and Routing Broadcast-Quality Composite-Video Multiplexing Workstations Video Editing Broadcast and High-Definition TV Systems Multimedia Products Medical Imaging
_________________Pin Configurations
TOP VIEW
IN1A 1 GND 2 IN2A 3 GND 4 IN3A 5 VCC 6 VEE 7 IN1B 8 GND 9 IN2B 10 GND 11 IN3B 12 24 GND 23 LE 22 EN 21 A0
MAX499
20 CS 19 OUT1 18 VCC 17 VEE 16 OUT2 15 N.C. 14 OUT3 13 N.C.
SO MAX498 appears at end of data sheet.
________________________________________________________________ Maxim Integrated Products
1
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Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers MAX498/MAX499
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC to VEE)................................................+12V Voltage on IN_ _ to GND ..................(VEE - 0.3V) to (VCC + 0.3V) Voltage on Digital Inputs (LE, EN, A0, CS) .........................................-0.3V to (VCC + 0.3V) Voltage on OUT_ (disabled) ..................................................4V Output Short-Circuit Duration to -4V OUT_ +4V ..................................................Continuous Continuous Power Dissipation (TA = +70C) 24-Pin SO (derate 11.76mW/C above +70C).............941mW 28-Pin SO (derate 12.5mW/C above +70C)......................1W Operating Temperature Range .................................0C to +70 Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering, 10sec) .............................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
DC ELECTRICAL CHARACTERISTICS
(VCC = +5V, VEE = -5V, VIN_ _ = 0V, RL = 150, LE = EN = CS = 0V, TA = 0C to +70C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER Input Voltage Range Voltage Gain Input Offset Voltage Input Offset Voltage Drift Input Bias Current Input Resistance Input Capacitance Output Short-Circuit Current Output Current On Output Resistance On Output Impedance Off Output Resistance Operating Supply-Voltage Range Positive Power-Supply Rejection Negative Power-Supply Rejection Logic Low Voltage Logic High Voltage Logic Input Current PSR+ PSRVINLL VINLH IINL 0V VINL VCC EN = 0 Positive Supply Current ICC EN = 1 EN = 0 Negative Supply Current IEE EN = 1 Note 1: 2 Limited by package power dissipation. MAX498 MAX499 MAX498 MAX499 MAX498 MAX499 MAX498 MAX499 -10 40 31 14 11 38 29 12 9 4.50V VCC 5.50V, VEE = -5.0V -5.50V VEE -4.5V, VCC = +5.0V SYMBOL VIN AV VOS TCVOS IB RIN CIN IOUT(SC) IOUT_ ROUT f = 10MHz -2.50V VOUT +2.50V 1.0 4.50 55 55 0.8 2 130 52 41 17 14 50 39 15 12 mA mA 72 72 -1.25V VIN +1.25V Channel on or off -3.5V OUT_ +3.5V (Note 1) -2.0V VOUT_ +2.0V, RL = 75 27 200 RL = 150, -1.25V VIN +1.25V RL = 75, -1.0V VIN +1.0V CONDITIONS MIN 1.25 1.985 1.965 2 50 1 700 2 120 40 0.15 3.0 1.2 5.50 7 TYP 1.70 2.030 2.030 9 MAX UNITS V V/V mV V/C A k pF mA mA k V dB dB V V A
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Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers
AC ELECTRICAL CHARACTERISTICS
(VCC = +5V, VEE = -5V, VIN_ _ = 0V, RL = 100, LE = EN = CS = 0V, TA = +25C, unless otherwise noted.) PARAMETER Small-Signal, -3dB Bandwidth 0.1dB Gain Flatness Full-Power, -3dB Bandwidth Slew Rate Settling Time Input Voltage Noise Density Input Current Noise Density Total Harmonic Distortion Spurious-Free Dynamic Range Adjacent-Channel Crosstalk All-Hostile Crosstalk Off-Isolation Differential Gain Differential Phase Diff Gain THD SFDR FPBW SR ts SYMBOL BW-3dB CONDITIONS VIN 100mVp-p VIN 100mVp-p VOUT = 2V VOUT = 4V step 0.1%, VOUT = 4V step f = 100kHz f = 100kHz f = 10MHz fC = 3MHz f = 10MHz (Note 2) f = 10MHz (Note 3) EN = 1, f = 10MHz (Note 4) f = 3.58MHz (Note 5), RL = 150 Diff Phase f = 3.58MHz (Note 5), RL = 150 MIN TYP 250 70 135 1250 12 7.8 2.6 -50 -66 90 62 81 0.03 0.06 MAX UNITS MHz MHz MHz V/s ns nV/Hz pA/Hz dB dBc dB dB dB % degrees
MAX498/MAX499
TIMING CHARACTERISTICS
(VCC = +5V, VEE = -5V, VIN_ _ = 0V, RL = 150, LE = EN = CS = 0V, TA = 0C to +70C. Typical values are at TA = +25C, unless otherwise noted.) PARAMETER A0/EN to CS Setup Time A0/EN to CS Hold Time CS Pulse Width Channel-Switching Propagation Delay Channel-Switching Time Channel-Switching Transient Enable/Disable Switching Transient Amplifier-Disable Time Amplifier-Enable Time Note 2: tOFF tON SYMBOL tSU tH tCS tPD tSW CONDITIONS LE = high (Note 6) LE = high (Note 6) (Note 6) (Note 7) (Note 8) VINA = VINB = 0V VINA = VINB = 0V (Note 9) (Note 10) Positive Negative Positive Negative 15 20 3 70 50 10 150 16 24 MIN 8 4 TYP MAX UNITS ns ns ns ns ns mV mV ns ns
Test-channel input grounded through a 50 resistor. Adjacent channel driven to a 2Vp-p output with a 10MHz sine wave (Figure 9). Note 3: Same as Note 2, except all channels but the test channel are driven to a 2Vp-p output with a 10MHz sine wave (Figure 9). Note 4: Test-channel input connected to a 2Vp-p sine wave at 10MHz. The test channel's output is measured with the outputs disabled (Figure 9). Note 5: Input test signal is a 3.58MHz sine wave of 40IRE amplitude, superimposed on a 0IRE to 100IRE linear ramp (Figure 10). Note 6: Guaranteed by design. Note 7: VINA = +1V, VINB = -1V, delay from CS to 10% of VOUT. Note 8: VINA = +1V, VINB = -1V, delay from CS to 10% of VOUT. Note 9: Delay from EN to 90% of VOUT. Note 10: Delay from EN to 10% of VOUT.
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Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers MAX498/MAX499
__________________________________________Typical Operating Characteristics
(VCC = +5V, VEE = -5V, RL = 100, TA = +25C, unless otherwise noted.)
SMALL-SIGNAL GAIN vs. FREQUENCY
MAX498/499-01
GAIN FLATNESS vs. FREQUENCY
MAX498/499-02
LARGE-SIGNAL GAIN vs. FREQUENCY
7 6 GAIN (dB) 5 4 3 2 1 0 VOUT = 2Vp-p
MAX498/499-03
8 7 6 5 GAIN (dB) 4 3 2 1 0 -1 1M 10M 100M VIN = 20mVp-p
6.2 6.1 6.0 5.9 GAIN (dB) 5.8 5.7 5.6 5.5 5.4 5.3 VIN = 20mVp-p
8
1G
1M
10M
100M
1G
1M
10M
100M
1G
FREQUENCY (Hz)
FREQUENCY (Hz)
FREQUENCY (Hz)
LARGE-SIGNAL GAIN vs. FREQUENCY
7 6 GAIN (dB) GAIN (dB) 5 4 3 2 1 0 1M 10M 100M 500M FREQUENCY (Hz) -0.06 -0.10 1M 0.06 0.02 -0.02 RL = 50 VOUT = 2Vp-p
MAX498/499-04
LARGE-SIGNAL GAIN vs. FREQUENCY
VOUT = 2Vp-p 0.10 OUT0-OUT1 OUT0-OUT3 IMPEDANCE ()
MAX498/499-05
OUTPUT IMPEDANCE vs. FREQUENCY
MAX498/499 TOC-06
8
0.14
1000
100
10
1
OUT0-OUT2
0.1
0.01 10M FREQUENCY (Hz) 100M 10k 100k 1M 10M 100M FREQUENCY (Hz)
OFF-ISOLATION vs. FREQUENCY
MAX498/499-07
CROSSTALK vs. FREQUENCY
0 -20 CROSSTALK (dB) PSR (dB) -40 -60 ADJACENT -80 -100 -120 -140 ALL HOSTILE VOUT = 2Vp-p
MAX498/499-08
POWER-SUPPLY REJECTION vs. FREQUENCY
-25 -35 -45 -55 -65 PSR+ -75 -85 -95 PSRMAX498/499-09
-20 -30 OFF-ISOLATION (dB) -40 -50 -60 -70 -80 -90 -100 1M 10M 100M
20
-15
1G
1M
10M FREQUENCY (Hz)
100M
30k 0.1M
1M
10M
100M
FREQUENCY (Hz)
FREQUENCY (Hz)
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Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers
____________________________Typical Operating Characteristics (continued)
(VCC = +5V, VEE = -5V, RL = 100, TA = +25C, unless otherwise noted.)
MAX498 SUPPLY CURRENT vs. TEMPERATURE
MAX498/499-10
MAX498/MAX499
DISABLED SUPPLY CURRENT vs. TEMPERATURE
EN = HIGH (OUTPUTS DISABLED) 14 CURRENT (mA) 13 12 11 10 9 IEE ICC
MAX498/499-11
GAIN vs. TEMPERATURE
MAX498/499-12
50
15
2.0200
SUPPLY CURRENT (mA)
45 ICC 40 IEE 35
SUPPLY CURRENT (mA)
2.0175 VIN = +1V 2.0150 VIN = -1V
2.0125
30 -55 -35 -15 5 25 45 65 85 TEMPERATURE (C)
8 -55 -35 -15 5 25 45 65 85 TEMPERATURE (C)
2.0100 -55 -35
-15
5
25
45
65
85
TEMPERATURE (C)
INPUT OFFSET VOLTAGE vs. TEMPERATURE
MAX498/499-13
INPUT BIAS CURRENT vs. TEMPERATURE
8 INPUT BIAS CURRENT (A) 6 4 2 0 -2 -4 -6 -8 -10
MAX498/499-14
12 10 8 6 4 VOS (mV) 2 0 -2 -4 -6 -8 -10 -12 -55 -35 -15 5 25 45 65
10
85
-55
-35
-15
5
25
45
65
85
TEMPERATURE (C)
TEMPERATURE (C)
LARGE-SIGNAL PULSE RESPONSE
MAX498/499 TOC-16
LARGE-SIGNAL PULSE RESPONSE (CL = 47pF)
MAX498/499 TOC-17
LARGE-SIGNAL PULSE RESPONSE (CL = 100pF)
+1 IN 0 VOLTAGE (V) -1
MAX498/499 TOC-18
+1 IN 0 VOLTAGE (V) -1
+1 IN 0 VOLTAGE (V) -1
+2 OUT 0 -2 TIME (10ns/div)
+2 OUT 0 -2 TIME (10ns/div)
+2 OUT 0 -2 TIME (10ns/div)
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Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers MAX498/MAX499
____________________________Typical Operating Characteristics (continued)
(VCC = +5V, VEE = -5V, RL = 100, TA = +25C, unless otherwise noted.)
SMALL-SIGNAL PULSE RESPONSE
MAX498/499 TOC-19
SMALL-SIGNAL PULSE RESPONSE (CL = 47pF)
+100 IN VOLTAGE (mV) 0 -100
MAX498/499 TOC-20
SMALL-SIGNAL PULSE RESPONSE (CL = 100pF)
+100 VOLTAGE (mV) IN 0 -100
MAX498/499 TOC-21
+100 IN VOLTAGE (mV) 0 -100
+200 0 -200 TIME (10ns/div)
+200 0 -200 TIME (10ns/div)
+200 0 -200 TIME (10ns/div)
OUT
OUT
OUT
CHANNEL SWITCHING
MAX498/499 TOC-22
ENABLE/DISABLE SWITCHING
MAX498/499 TOC-23
CHANNEL-SWITCHING TRANSIENT
+5 A0 VOLTAGE (V) 0
MAX498/499 TOC-24
+2 VOLTAGE (V) OUT_ 0 -2 +5 A0 0 TIME (10ns/div) IN_A = -1V IN_B = +1V
+2 VOLTAGE (V) OUT 0 +5
+100m OUT_ 0 -100m
ENABLE 0 TIME (10ns/div)
TIME (50ns/div)
ENABLE/DISABLE SWITCHING TRANSIENT
MAX498/499 TOC-25
BANDWIDTH vs. INPUT VOLTAGE
280 260 BANDWIDTH (MHz) 240 220 200 180 160
MAX498/499-26
300
+5 ENABLE VOLTAGE (V) 0
+100m 0 OUT_ -100m
TIME 50ns/div
140 120 0.01 0.1 1 10
INPUT VOLTAGE (Vp-p)
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Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers
______________________________________________________________Pin Description
PIN NAME MAX498 1, 3, 5, 11, 13, 19 2 4 6 7, 22 8 9, 21 10 12 14 15, 17 16 18 20 23 24 MAX499 2, 4, 9, 11, 24 1 3 5 6, 18 -- 7, 17 8 10 12 13, 15 14 16 19 -- 20 GND IN1A IN2A IN3A VCC IN0B VEE IN1B IN2B IN3B N.C. OUT3 OUT2 OUT1 OUT0 CS Analog Ground. All ground pins are internally connected. Connect all ground pins externally to ground to minimize impedance. Signal Input 1, Channel A Signal Input 2, Channel A Signal Input 3, Channel A Positive Power-Supply Voltage. Connect VCC to +5V. VCC pins are internally connected. Connect both pins externally to +5V to minimize supply impedance. Bypass each pin to ground with a 0.1F ceramic capacitor. Signal Input 0, Channel B Negative Power-Supply Voltage. Connect VEE to -5V. VEE pins are internally connected. Connect both pins to -5V externally to minimize supply impedance. Bypass each pin to ground with a 0.1F ceramic capacitor. Signal Input 1, Channel B Signal Input 2, Channel B Signal Input 3, Channel B No Connect. Not internally connected; connect to GND. Output 3 Output 2 Output 1 Output 0 Chip-Select Input. When CS is low, the A0 and EN latches are transparent. The data present at A0 is latched when CS goes high. LE's status determines whether EN is latched along with A0, or if the EN latch remains transparent independently of CS. Address Input. A0 = 0 selects channel A, and A0 = 1 selects channel B if CS is low. A0 is latched on CS's low-to-high transition. Output Buffer-Enable Input. EN = 0 enables the output buffer amplifiers, and EN = 1 disables the output buffers if CS is low. EN is latched during CS's low-to-high transition if LE is high. EN is not latched if LE is low. Latch-Enable Input. With LE = 1, EN is latched along with A0 when CS goes high. When LE = 0, the EN latch is transparent independently of CS's state. Signal Input 0, Channel A FUNCTION
MAX498/MAX499
25
21
A0
26
22
EN
27 28
23 --
LE IN0A
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Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers MAX498/MAX499
1 GND IN0A 28
2
IN1A
LE
27
3
GND
EN
26
4
IN2A
A0
25
5
GND
CS
24
6
IN3A
MAX498
OUT0
23
+5VDC 10F 0.1F
7
VCC
VCC
22 0.1F
+5VDC
8
IN0B
VEE
21 0.1F
-5VDC
-5VDC 10F 0.1F
9
VEE
OUT1
20
10
IN1B
GND
19
11
GND
OUT2
18
12
IN2B
N.C.
17
13
GND
OUT3
16
14
IN3B EIGHT-IN/FOUR-OUT VIDEO MUX AMP
N.C.
15
NOTE: ALL RESISTORS ARE 50 OR 75
Figure 1a. MAX498 Typical Application Circuit
8 _______________________________________________________________________________________
Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers MAX498/MAX499
1
IN1A
GND
24
2
GND
LE
23
3
IN2A
EN
22
4
GND
A0
21
5
IN3A
CS
20
+5VDC 10F 0.1F
6
VCC
MAX499
OUT1
19
+5VDC 10F 0.1F
7
VEE
VCC
18 0.1F
+5VDC
8
IN1B
VEE
17 0.1F
-5VDC
9
GND
OUT2
16
10
IN2B
N.C.
15
11
GND
OUT3
14
12
IN3B
N.C.
13
SIX-IN/THREE-OUT VIDEO MUX AMP
NOTE: ALL RESISTORS ARE 50 OR 75
Figure 1b. MAX499 Typical Application Circuit
_______________________________________________________________________________________ 9
Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers MAX498/MAX499
______________ Detailed Description
The MAX498/MAX499 are quad/triple video switches with high-speed, closed-loop, voltage-feedback amplifiers set to a 2V/V gain. Figure 1 shows typical application circuits. The amplifiers use a unique two-stage, voltage-feedback architecture that combines the benefits of conventional voltage-feedback and currentfeedback topologies to achieve wide bandwidths and high slew rates while maintaining precision. Figure 2 is a simplified block diagram of the MAX498/ MAX499. All four amplifier/switch blocks are identical to that shown for Ch_0. A common control logic block accepts external logic inputs A0, EN, CS, and LE, and controls the status of switches S1, S2, and S3 of each amplifier in parallel, as described in the Digital Interface section. S3 is open in the enabled state, and if Ch_A is selected, S1 is connected to IN_A and S2 is connected to GND. If Ch_B is selected, S1 is connected to GND and S2 is connected to IN_B. Connecting the deselected GM_ block to GND ensures minimum feedthrough. S3 is closed in the disabled state, and both S1 and S2 are connected to GND. Disconnecting both inputs and connecting the amplifier's inputs to GND significantly improves off-isolation.
IN0A GM_A S1 X1 CC IN0B S2 GM_B X1 RFB S3 R0
MAX498 MAX499
CHANNEL 0 OUT0
RG
CHANNEL 1 CHANNEL 2 CHANNEL 3 S1 A0 EN CS LE CONTROL LOGIC S2 S3
__________Applications Information
Power Dissipation
The MAX498/MAX499's maximum output current is limited by the package's maximum allowable power dissipation. The maximum junction temperature should not exceed +150C. Power dissipation increases with load, and this increase can be approximated by one of the following equations: For VOUT > 0V: |VCC - VOUT| ILOAD OR For VOUT < 0V: |VEE - VOUT| ILOAD. These devices can drive 100 loads connected to each of the outputs over the entire rated output swing and temperature range. While the output is short-circuit protected to 120mA, this does not necessarily guarantee that under all conditions, the maximum junction temperature will not be exceeded. Do not exceed the derating values given in the Absolute Maximum Ratings section.
Figure 2. Block Diagram
Total Noise
The MAX498/MAX499's low 2.6pA/Hz input current noise and 7.8nV/Hz voltage noise provide for lower total noise compared to typical current-mode feedback amplifiers, which usually have significantly higher input current noise. The input current noise multiplied by the feedback resistor is the dominant noise source of current-mode feedback amplifiers.
Differential Gain and Phase Errors
Differential gain and phase errors are critical specifications for a buffer in composite (NTSC, PAL, SECAM) video applications, because these errors correspond directly to color changes in the displayed picture of composite video systems. The MAX498/MAX499's low differential gain and phase errors (0.03%/0.06) make them ideal in broadcastquality, composite video applications.
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Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers
MAX186/MAX188 FULL POWER-DOWN
14 12 10 8 GAIN (dB) 6 4 2 0 -2 -4 -6 1M 10M 100M 1G FREQUENCY (Hz) 0pF RISO = 0 100pF 47pF GAIN (dB) 14 12 10 8 6 4 2 0 -2 -4 -6 1M 10M 100M 1G FREQUENCY (Hz) 0pF
MAX186/MAX188 FULL POWER-DOWN
RISO = 6.8 150pF 100pF 47pF
MAX498/MAX499
Figure 3a. Small-Signal Gain vs. Frequency and Load Capacitor (RL = 100, RISO = 0)
Figure 3b. Small-Signal Gain vs. Frequency and Load Capacitor (RL = 100, RISO = 6.8)
VIN VOLTAGE (V)
+1 -1 VOLTAGE (mV) TIME (10ns/div)
+100 VIN -100
+2 VOUT -2
+200 VOUT -200
TIME (10ns/div)
Figure 4a. Large-Signal Pulse Response with CL = 100pF and RISO = 5.1
Figure 4b. Small-Signal Pulse Response with CL = 100pF and RISO = 5.1
Coaxial Cable Drivers
High-speed performance, excellent output current capability, and an internally fixed gain of +2 make the MAX498/MAX499 ideal for driving back-terminated 50 or 75 coaxial cables to 2.5V. In a typical application, the MAX498/MAX499 drive a back-terminated cable (Figure 1). The back-termination resistor, at the output, matches the impedance of the cable's driven end to the cable's impedance, eliminating signal reflections. This resistor, along with the loadtermination resistor, forms a voltage divider with the load impedance, which attenuates the signal at the cable's output by one-half. The MAX498/MAX499 operate with an internal +2V/V closed-loop gain to provide unity gain at the cable's output.
Capacitive-Load Driving
In most amplifier circuits, driving large capacitive loads increases the likelihood of oscillation. This is especially true for circuits with high loop gains, such as voltage followers. The amplifier's output resistance and the capacitive load form an RC filter that adds a pole to the loop response. If the pole frequency is low enough (as when driving a large capacitive load), the circuit-phase margin is degraded and oscillation may occur. The MAX498/MAX499 drive capacitive loads up to 100pF without sustained oscillation, although some peaking may occur (Figures 3a and 3b). When driving larger capacitive loads, or to reduce peaking, add an isolation resistor (RISO) between the output and the capacitive load (Figures 4a, 4b, and 5).
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Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers MAX498/MAX499
COMPARATOR INPUT BIAS CURRENT vs. SUPPLY VOLTAGE
8 7 ISOLATION RESISTOR () 6 5 4 3 2 47 100 150 200 270 390 510 CAPACITANCE (pF) DISTORTION (dBc) -82 -84 -86 -88 -90 -92 -94 -96 -98 10 100 1k 10k FREQUENCY (Hz)
MAX186/MAX188 FULL POWER-DOWN
Figure 5. Isolation Resistor vs. Capacitive Load
Figure 6. Total Harmonic Distortion (Audio) vs. Frequency
Switching Audio Signals (Audio-Distortion Measurement)
When switching audio signals, distortion is the prime consideration in performance. Figure 6 shows total harmonic distortion vs. frequency, in the audio range, for the MAX498/MAX499.
Digital Interface
The MAX498/MAX499 multiplexer architecture ensures that no input channels are ever connected together. Select a channel by changing A0's state (A0 = 0 for channel A, and A0 = 1 for channel B) and pulsing CS low (see Tables 1a and 1b). Figure 7 shows the logic timing diagram. -- - When the enable input (EN) is driven to a TTL low state, - it -- enables the MAX498/MAX499 amplifier outputs. When EN is driven high, it disables the amplifier outputs. When disabled, the MAX498/MAX499 exhibit a 1.2k disabled output resistance due to their internal feedback resistors. -- - LE determines whether EN is latched by CS or operates independently. When the latch-enable input (LE) is con-- - nected to V+, CS becomes the latch-- control for the EN - input register. If CS is low, both the EN and A0 latches -- - are transparent; once CS returns high, both A0 and EN are latched. -- - When LE is connected to ground, the EN latch is transparent and independent of CS. This allows all MAX498/MAX499 devices to be shut down simultaneously, regardless of CS's input state. Simply connect -- - LE to ground and connect all E N inputs together (Figure 8a). Hard wire LE to V+ or ground (rather than driving LE with a gate) to prevent crosstalk from the digital inputs to IN0A.
Large Switch Arrays
Large crosspoint switch arrays are possible with the MAX498/MAX499 using the enable function EN. When the amplifiers are disabled, output impedance is typically 1.2k, due to the feedback and gain resistors. This limits the number of outputs that can be paralleled without a buffer. Since each output can drive 100, eight outputs can typically be connected together. If additional outputs must be connected in parallel, a MAX4178 (single), MAX496 (quad), or equivalent unitygain buffer can be used. Whether enabled or disabled, each input represents more than 200k of resistance. Capacitance is the prime consideration limiting the number of inputs that can be connected to a single output. Since each output can drive 100pF of capacitance without an isolation resistor, 50 inputs (CIN = 2pF, typical) can be driven by a single output. However, peaking will occur as inputs are added (Figure 3), which reduces the 0.1dB bandwidth.
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Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers
Another option for output disable is to connect LE to V+, parallel the outputs of several MAX498/MAX499s, and use -- - EN to individually disable all devices but the one in use (Figure 8b). When the outputs are disabled, off-isolation from the analog inputs to the amplifier outputs is typically 81dB at 10MHz.
MAX498/MAX499
Table 1a. Amplifier and Channel Selection with LE = V+ FUNCTION CS EN A0
0 0 0 1 0 0 1 X 0 1 X X Enables amplifier outputs. Selects channel A. Enables amplifier outputs. Selects channel B. Disables amplifiers. Outputs high-Z. Latches A0, EN. Outputs unchanged.
Grounding and Layout
The MAX498/MAX499 bandwidths are in the RF frequency range. Depending on the size of the PC board used and the frequency of operation, it may be necessary to use Micro-strip or Stripline techniques. To realize the full AC performance of these high-speed buffers, pay careful attention to power-supply bypassing and board layout. The PC board should have at least two layers (wire-wrap boards are too inductive, and bread boards are too capacitive), with one side a signal layer and the other a large, low-impedance ground plane. With multilayer boards, locate the ground plane on the layer that is not dedicated to a specific signal trace. The ground plane should be as free from voids as possible. Connect all ground pins to the ground plane. Connect both positive power-supply pins together and bypass with a 0.10F ceramic capacitor at each powersupply pin, as close to the device as possible. Repeat for the negative power-supply pins. The capacitor lead lengths should be as short as possible to minimize lead inductance; surface-mount chip capacitors are ideal. A large-value (10F or greater) tantalum or electrolytic bypass capacitor on each supply may be required for high-current loads. The location of this capacitor is not critical. The MAX498/MAX499's analog input pins are isolated with ground pins to minimize parasitic coupling, which can degrade crosstalk and/or amplifier stability. Keep signal paths as short as possible to minimize inductance. Ensure that all input channel traces are the same length, to maintain the phase relationship between the four channels. To further reduce crosstalk, connect the coaxial-cable shield to the ground side of the 75 terminating resistor at the ground plane, and terminate all unused inputs to ground and outputs with a 100 or 150 resistor to ground.
Table 1b. Amplifier and Channel Selection with LE = GND FUNCTION CE EN A0
0 1 X 0 0 0 1 0 0 X X 1 Enables amplifier outputs. Selects channel A. Enables amplifier outputs. Latches A0 to output A or B, according to A0's -- - state at CS's last edge. Disables amplifiers. Outputs high-Z. A0 latch = channel A. Enables amplifier outputs. Selects channel B.
______________________________________________________________________________________
13
Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers MAX498/MAX499
CS
tCS
tSU tH
A0
tSU tH
EN
tPD
OUTPUTS
tOFF
tON
tSW
LE = V+
Figure 7. Logic Timing Diagram
EN AO LE CS
SHUTDOWN
EN
MAX498 MAX499
+5V LE
MAX498 MAX499
EN AO LE CS
MAX498 MAX499
EN NOTE: ISOLATION RESISTORS (IF REQUIRED) NOT SHOWN.
+5V LE
MAX498 MAX499
(a)
(b)
-- -- -- -- Figure 8. (a) Simultaneous Shutdown of all MAX498/MAX499s; (b) Enable (EN) Register Latched by CS
14
______________________________________________________________________________________
Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers MAX498/MAX499
MAX498/MAX499 MAX498/MAX499
50
100
50
100
VIN = 4Vp-p, f = 10MHz, RS = 75
50
100
50
100
50
100
50
100
50
100
VIN = 4Vp-p, f = 10MHz, RS = 75
50
100
a) ADJACENT CHANNEL
b) ALL HOSTILE
Figure 9. Test Circuits for Measuring Crosstalk: a) Adjacent Channel; b) All Hostile
75 CABLE
75 75 CABLE DUT SOURCE: TEKTRONIX 1910 DIGITAL GENERATOR 75 75 MEASUREMENT: TEKTRONIX VM700 VIDEO MEASUREMENT SET
MAX499
75
75 CABLE
Figure 10. Differential Phase and Gain Error Test Circuit
______________________________________________________________________________________
15
Quad/Triple, SPDT, RGB Switches with 250MHz Video Buffer Amplifiers MAX498/MAX499
____Pin Configurations (continued)
TOP VIEW
GND 1 IN1A 2 GND 3 IN2A 4 GND 5 IN3A 6 VCC 7 IN0B 8 VEE 9 IN1B 10 GND 11 IN2B 12 GND 13 IN3B 14 28 IN0A 27 LE 26 EN 25 A0
___________________Chip Information
SUBSTRATE CONNECTED TO: VEE TRANSISTOR COUNT: 813
MAX498
24 CS 23 OUT0 22 VCC 21 VEE 20 OUT1 19 GND 18 OUT2 17 N.C. 16 OUT3 15 N.C.
SO
________________________________________________________Package Information
DIM INCHES MAX MIN 0.104 0.093 0.012 0.004 0.019 0.014 0.013 0.009 0.299 0.291 0.050 0.419 0.394 0.050 0.016 MILLIMETERS MIN MAX 2.35 2.65 0.10 0.30 0.35 0.49 0.23 0.32 7.40 7.60 1.27 10.00 10.65 0.40 1.27
D 0- 8 A e B
0.101mm 0.004in.
A1
C
L
A A1 B C E e H L
DIM PINS
E
H
Wide SO SMALL-OUTLINE PACKAGE (0.300 in.)
D D D D D
16 18 20 24 28
INCHES MIN MAX 0.398 0.413 0.447 0.463 0.496 0.512 0.598 0.614 0.697 0.713
MILLIMETERS MIN MAX 10.10 10.50 11.35 11.75 12.60 13.00 15.20 15.60 17.70 18.10
21-0042A
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
16 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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