19-1398; Rev 4; 5/07 KIT ATION EVALU E L B A IL AVA Upstream CATV Amplifier Features The MAX3510 is a programmable power amplifier for use in CATV upstream applications. The device outputs up to 64dBmV (continuous wave) through a 2:1 (voltage ratio) transformer. It features variable gain controlled by a 3-wire digital serial bus. Gain control is available in 1dB steps. The device operates over a frequency range of 5MHz to 65MHz. ♦ Ultra-Low Power-Up/Down Transients, 7mV Typical at 59dBmV Output The MAX3510 offers a transmit-disable mode, which places the device in a high-isolation state for use between bursts in TDMA systems. In this mode the output stage is shut off, minimizing output noise. When entering and leaving transmit-disable mode, transients are kept to 7mV nominal at full gain. In addition, supply current is reduced to 25mA. Two power-down modes are available. Software-shutdown mode permits power-down of all analog circuitry while maintaining the programmed gain setting. Shutdown mode disables all circuitry and reduces current consumption to less than 10µA. The MAX3510 is available in a 20-pin QSOP package for the extended-industrial temperature range (-40°C to +85°C). ♦ Low Transmit Output Noise Floor: -47dBmV (160kHz BW) ♦ Single +5V Supply ♦ Output Level Ranges from <8dBmV to 64dBmV ♦ Gain Programmable in 1dB Steps ♦ Low Transmit-Disable Output Noise: -70dBmV ♦ Two Power-Down Modes Ordering Information PART TEMP RANGE PIN-PACKAGE MAX3510EEP -40°C to +85°C 20 QSOP MAX3510EEP+ -40°C to +85°C 20 QSOP +Denotes lead-free package. Applications Cable Modems CATV Set-Top Boxes Telephony-Over-Cable CATV Status Monitors Pin Configuration appears at end of data sheet. Typical Operating Circuit 12 CONTROL LOGIC SHDN GND2 TXEN VCC2 19 18 CEXT1 0.001µF 5 + 0.0033µF 6 0.1µF OUTPUT +5V MAX3510 +5V 2:1 16 ANTI-ALIAS FILTER – 0.1µF +5V 17 VIN+ VOUT+ INPUT 20 0.001µF 2 4 3 7 1 VIN- VOUT- 15 0.1µF 0.1µF VCC1 GND1 GND CEXT2 N.C. GND 14 13 11 10 SCLK GND GND SDA CS 9 8 CONTROL LOGIC ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX3510 General Description MAX3510 Upstream CATV Amplifier ABSOLUTE MAXIMUM RATINGS VCC (VCC1, VCC2), VOUT+, VOUT- ................... -0.5V to +10.0V Input Voltage Levels (all inputs), CEXT1, CEXT2.........................................-0.3V to (VCC + 0.3V) Continuous Input Voltage (VIN+, VIN-) ...............................2VP-P Continuous Current (VOUT+, VOUT-).................................80mA Continuous Power Dissipation (TA = +70°C) 20-Pin QSOP (derate at 12.3mW/°C above +70°C)....1067mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +165°C Lead Temperature (soldering, 10s) .................................+300°C 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 = +4.75V to +5.25V, TXEN = SHDN = high, D7 = 1, TA = -40°C to +85°C, unless otherwise noted. No input signal applied. Typical parameters are at TA = +25°C.) PARAMETER SYMBOL MAX UNITS 5.25 V 109 126 mA TXEN = low 26 30 mA ICC TXEN = low, D7 = 0 (Note 3) 1.4 mA Supply Current Shutdown Mode ICC SHDN = low, TXEN = low 1 µA Input High Voltage VINH TA = 25°C Input Low Voltage VINL TA = 25°C 0.8 V Input High Current IBIASH (Note 3) 100 µA Input Low Current IBIASL (Note 3) Supply Voltage VCC Supply Current Transmit Mode ICC Supply Current Transmit-Disable Mode ICC Supply Current SoftwareShutdown Mode CONDITIONS MIN TYP 4.75 2.0 V -100 µA AC ELECTRICAL CHARACTERISTICS (VCC = +4.75V to +5.25V, TXEN = SHDN = high, D7 = 1, VIN = 34dBmV differential, output impedance = 75Ω through a 2:1 transformer, TA = -40°C to +85°C, unless otherwise noted. Typical parameters are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN TYP Gain-control word = 1, TA = -40°C to +85°C Voltage Gain AV fIN = 5MHz to 42MHz (Note 3) fIN = 10MHz (Note 3) Bandwidth Output Step Size 2 Gain-control word = 63, TA = -40°C to 0°C 26 Gain-control word = 50, TA = -40°C to +85°C 16.7 P1dB VOUT = 60dBmV, fIN = 42MHz VOUT = 60dBmV, fIN = 65MHz AV = 26dB, 42MHz (Note 1) Gain Rolloff (Notes 1, 2) 1dB Compression Point 27 VOUT = 60dBmV, -3dB (Note 1) fIN = 5MHz to 42MHz (Note 3) UNITS -26 Gain-control word = 63, TA = 0°C to +85°C f3dB MAX dB 20.4 84 100 -1 -1.8 MHz 18.0 -0.9 -1.6 20.0 AV = -26dB to +27dB, TA = -0°C to +85°C 0.6 1 1.4 AV = -26dB to +26dB, TA = -40°C to 0°C 0.6 1 1.4 dB dBm dB _______________________________________________________________________________________ Upstream CATV Amplifier (VCC = +4.75V to +5.25V, TXEN = SHDN = high, D7 = 1, VIN = 34dBmV differential, output impedance = 75Ω through a 2:1 transformer, TA = -40°C to +85°C, unless otherwise noted. Typical parameters are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS Transmit Mode Noise (Note 1) BW = 160kHz, AV = -26dB Transmit-Disable Mode Noise Floor TXEN = low, BW = 160kHz, AV = +26dB, fIN = 5MHz to 65MHz (Note 1) Isolation in Transmit-Disable Mode TXEN low, gain control word = 61, fIN = 65MHz TXEN Transient Duration TXEN rise/fall time < 0.1µs, TA = +25°C (Note 1) TXEN Transient Step Size (Note 1) Gain = 26dB, TA = +25°C ⏐ZIN⏐ Output Impedance ZOUT Output Return Loss in Transmit-Disable Mode Two-Tone Third-Order Distortion (Note 1) 2nd Harmonic Distortion RL RL fIN = 5MHz to 65MHz, single-ended, TA = +25°C (Note 1) 36 fIN = 5MHz to 65MHz (Note 1) TXEN = low, fIN = 5MHz to 65MHz (Note 1) MAX dBc -46 dBmV -70 dBmV 45 3.2 dB 5 7 37 0.7 3.7 mVP-P kΩ 75 Ω TA = 0°C 8.0 13.5 TA = +25°C 8.7 13.5 TA = +85°C 8.9 13.9 TA = 0°C 7.1 12.0 TA = +25°C 7.7 12.2 TA = +85°C 9.7 12.7 -56 dB dB -53 IM3 HD3 µs 1.5 Input tones at 40MHz and 40.2MHz, VIN = 28dBmV/tone, VOUT = +54dBmV/tone, TA = +25°C HD2 UNITS -78 1.4 dBc Input tones at 65MHz and 65.2MHz, VIN = 28dBmV/tone, VOUT = 53dBmV/tone, TA = +25°C -54 -51 VOUT = +54dBmV -59 -53 VOUT = +59dBmV -55 -50 -54 -50 VOUT = +54dBmV -58 -53 VOUT = +59dBmV -54 -50 fIN = 65MHz, VOUT = +59dBmV, TA = +25°C (Note 1) -49 -44 fIN = 33MHz, (Note 3) TA = -40°C to +85°C fIN = 65MHz, VOUT = +59dBmV, TA = +25°C (Note 1) 3rd Harmonic Distortion TYP 47 Gain = 2dB or lower, TA = +25°C Input Impedance Output Return Loss in Transmit Mode MIN BW = 160kHz, AV = 26dB fIN = 22MHz, TA = -40°C to +85°C dBc dBc dBc AM to AM AM/AM AV = 26dB, VIN swept from 34dBmV to 38dBmV (Note 1) 0.1 dB AM to PM AM/PM AV = 26dB, VIN swept from 34dBmV to 38dBmV (Note 1) 1 degrees _______________________________________________________________________________________ 3 MAX3510 AC ELECTRICAL CHARACTERISTICS (continued) TIMING CHARACTERISTICS (VCC = +4.75V to +5.25V, TXEN = SHDN = high, D7 = 1, TA = +25°C, unless otherwise noted.) PARAMETER SYMBOL COMMENT MIN TYP MAX UNITS CS to SCK Rise Setup Time tSENS 10 ns CS to SCK Rise Hold Time tSENH 20 ns SDA to SCK Setup Time tSDAS 10 ns SDA to SCK Hold Time tSDAH 20 ns SDA Pulse-Width High tDATAH 50 ns SDA Pulse-Width Low tDATAL 50 ns SCK Pulse-Width High tSCKH 50 ns SCK Pulse-Width Low tSCKL 50 ns Note 1: Guaranteed by design and characterization. Note 2: Reference to 5MHz. Note 3: Parameters <25°C guaranteed by design and characterization ±3. Typical Operating Characteristics (VCC = +5V, VIN = +34dBmV, TXEN = SHDN = high, fIN = 20MHz, ZLOAD = 75Ω through a 2:1 transformer, TA = +25°C, unless otherwise noted.) VOLTAGE GAIN vs. SUPPLY VOLTAGE (GAIN STATE = 33) 108 VCC = 4.75V 106 0°C 1.2 0.8 +25°C 104 0.4 102 0 MAX3510 toc03 -40°C 1.6 26.8 VOLTAGE GAIN (dB) VCC = 5.25V VOLTAGE GAIN (dB) SUPPLY CURRENT (mA) 110 2.0 MAX3510 toc01 112 VOLTAGE GAIN vs. SUPPLY VOLTAGE (GAIN STATE = 60) MAX3510 toc02 SUPPLY CURRENT vs. TEMPERATURE -40°C +25°C +85°C +85°C 25 50 75 100 26.6 4.75 4.8 4.85 4.9 4.95 5.0 5.05 5.1 5.15 5.2 5.25 4.75 4.8 4.85 4.9 4.95 5.0 5.05 5.1 5.15 5.2 5.25 SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V) TEMPERATURE (°C) VOLTAGE GAIN vs. TEMPERATURE (GAIN STATE = 33) VOLTAGE GAIN vs. FREQUENCY 40 MAX3510 toc04 1.6 1.4 20 VOLTAGE GAIN (dB) 1.2 1.0 5.0V 0.8 5.25V 0.6 4.75V 0.4 D 0 -10 E -20 F -30 G 0 -60 -50 -25 0 25 50 TEMPERATURE (°C) 75 100 1 f = 5MHz 10 0 f = 40MHz -10 -20 GAIN-CONTROL WORD: A = 63 C = 48 E = 24 G = 6 B = 57 D = 36 F = 12 -50 30 20 10 -40 0.2 4 A B C 30 VOLTAGE GAIN vs. GAIN-CONTROL WORD 40 MAX3510 toc06 0 VOLTAGE GAIN (dB) -25 MAX3510 toc05 -50 VOLTAGE GAIN (dB) MAX3510 Upstream CATV Amplifier 10 -30 -40 100 FREQUENCY (MHz) 1000 0 6 12 18 24 30 36 42 48 54 60 GAIN-CONTROL WORD (DECIMAL) _______________________________________________________________________________________ Upstream CATV Amplifier otherwise noted.) VOLTAGE GAIN vs. GAIN-CONTROL WORD 26 1.15 GAIN STEP (dB) f = 40MHz 24 f = 5MHz 22 20 f = 60MHz MAX3510 toc10 MAX3510 toc08 28 VOLTAGE GAIN (dB) 1.25 MAX3510 toc07 30 OUTPUT IMPEDANCE (75Ω REFERENCE) GAIN STEP vs. GAIN-CONTROL WORD 5MHz 1.05 TRANSMIT-DISABLE MODE 0.95 TRANSMIT MODE 18 0.85 65MHz 16 14 0.75 50 52 54 56 58 60 62 64 6 12 18 24 30 36 42 48 54 60 GAIN-CONTROL WORD (DECIMAL) OUTPUT RETURN LOSS vs. FREQUENCY TRANSMIT OUTPUT NOISE vs. GAIN TRANSMIT-DISABLE MODE 12 16 -25 TRANSIENT LEVEL (mVP-P) TRANSMIT MODE 8 100 MAX3510 toc12 OUTPUT NOISE (dBmV IN 160kHz) 4 POWER-UP/POWER-DOWN TRANSIENTS vs. OUTPUT LEVEL -20 MAX3510 toc11 0 -30 -35 -40 3 9 15 21 27 0 10 GAIN (dB) FREQUENCY (MHz) VOUT = 60dBmV VOUT = 57dBmV -55 -60 VOUT = 6dBmV -65 40 50 60 VOUT = 30dBmV -70 -75 -35 MAX3510 toc15 -45 30 3rd HARMONIC DISTORTION vs. INPUT FREQUENCY 3rd HARMONIC DISTORTION (dBc) -40 20 OUTPUT LEVEL (dBmV) 2nd HARMONIC DISTORTION vs. INPUT FREQUENCY AND OUTPUT LEVEL -50 1 0.1 -33 -27 -21 -15 -9 -3 15 25 35 45 55 65 75 85 95 105 MAX3510 toc14 5 10 -45 -50 20 2nd HARMONIC DISTORTION (dBc) RETURN LOSS (dB) 0 GAIN-CONTROL WORD (DECIMAL) MAX3510 toc13 48 -40 -45 VOUT = 60dBmV -50 VOUT = 54dBmV -55 VOUT = 48dBmV -60 VOUT = 24dBmV -65 VOUT = 6dBmV -70 -80 -75 0 10 20 30 40 50 FREQUENCY (MHz) 60 70 0 10 20 30 40 50 60 70 INPUT FREQUENCY (MHz) _______________________________________________________________________________________ 5 MAX3510 Typical Operating Characteristics (continued) ( VCC = +5V, VIN = +34dBmV, TXEN = SHDN = high, fIN = 20MHz, ZLOAD = 75Ω through a 2:1 transformer, TA = +25°C, unless MAX3510 Upstream CATV Amplifier Table 1. Reflection Coefficients (75Ω reference) FREQUENCY TRANSMIT MODE TRANSMIT MODE TRANSMIT DISABLE MODE MHz REAL S11 IMAG S11 REAL S22 IMAG S22 REAL S22 IMAG S22 1 0.937 -0.006 -0.494 0.625 -0.509 0.623 2 0.937 -0.007 -0.054 0.550 -0.075 0.577 0.257 5 0.936 -0.005 0.196 0.199 0.219 10 0.932 -0.011 0.183 0.017 0.244 0.062 20 0.932 -0.018 0.143 -0.081 0.219 -0.052 30 0.932 -0.026 0.108 -0.149 0.194 -0.121 40 0.927 -0.033 0.059 -0.199 0.158 -0.175 60 0.922 -0.054 -0.060 -0.257 0.066 -0.252 80 0.913 -0.075 -0.197 -0.252 -0.049 -0.284 120 0.889 -0.145 -0.420 -0.070 -0.281 -0.207 160 0.850 -0.249 -0.442 0.256 -0.409 0.037 200 0.753 -0.408 -0.212 0.543 -0.327 0.345 Pin Description 6 PIN NAME 1, 3, 7, 11 FUNCTION GND Ground Pins 2 VCC1 Programmable-Gain Amplifier (PGA) +5V Supply. Bypass this pin to GND1 with a decoupling capacitor as close to the part as possible. 4 GND1 PGA RF Ground. As with all ground connections, maintain the shortest possible (low-inductance) length to the ground plane. 5 VIN+ Positive PGA Input. Along with VIN-, this port forms a high-impedance differential input to the PGA. Driving this port differentially will increase the rejection of second-order distortion at low output levels. 6 VIN- Negative PGA Input. When not used, this port must be AC-coupled to ground. See VIN+. 8 CS 9 SDA Serial-Interface Data. TTL-compatible input. See the Serial Interface section. 10 SCLK Serial-Interface Clock. TTL-compatible input. See the Serial Interface section. 12 SHDN Shutdown. When this pin and TXEN (pin 18) are set low, all functions (including the serial interface) are disabled, leaving only leakage currents to flow. Serial-Interface Enable. TTL-compatible input. See the Serial Interface section. 13 N.C. 14 CEXT2 No Connection RF Output Bypass. This pin must be bypassed to ground with a 0.1µF capacitor. 15 VOUT- Negative Output. Along with VOUT+, this port forms a 300Ω impedance output. This port is matched to a 75Ω load using a 2:1 transformer. 16 VOUT+ Positive Output. See VOUT-. 17 CEXT1 Transmit-Disable (Enable) Timing Capacitor. See the Ramp Generator section. 18 TXEN Power-Amplifier Enable. Setting this pin low shuts off the power amplifier. 19 VCC2 Power Amplifier Bias, +5V Supply. Bypass this pin to GND2 with a decoupling capacitor as close to the part as possible. 20 GND2 Power Amplifier Bias Ground. As with all ground connections, maintain the shortest possible (low inductance) length to the ground plane. _______________________________________________________________________________________ Upstream CATV Amplifier MAX3510 VOUT- SHDN VCC1 MAX3510 PGA BIAS CELL CEXT2 VOUT+ VIN+ VIN- VCC2 DAC SERIAL DATA INTERFACE CS RAMP GENERATOR POWER AMP BIAS TXEN CEXT1 SDA SCLK Figure 1. Functional Diagram Detailed Description The following sections describe the blocks shown in the functional diagram (Figure 1). Programmable-Gain Amplifier The programmable-gain amplifier (PGA) consists of the variable-gain amplifier (VGA) and the digital-to-analog converter (DAC), which provide better than 52dB of output level control in 1dB steps. The PGA is implemented as a programmable Gilbertcell attenuator. It uses a differential architecture to achieve maximum linearity. The gain of the PGA is determined by a 6-bit word (D5–D0) programmed through the serial data interface (Tables 2 and 3). Specified performance is achieved when the input is driven differentially. The device may be driven singleended; however, a slight increase in even-order distortion may result at low output levels. To drive the device in this manner, one of the input pins must be capacitively coupled to ground. Use a capacitor value large enough to allow for a low-impedance path to ground at the lowest frequency of operation. For operation down to 5MHz, a 0.001µF capacitor is suggested. Power Amplifier The power amplifier is a Class A differential amplifier capable of driving +64dBmV differentially. This architecture provides superior even-order distortion performance but requires that a transformer be used to convert to a single-ended output. In transmit-disable mode, the power amplifier is shut off. An internal resistor is placed across the output, so that the output impedance remains matched when the amplifier is in transmit-disable mode. Disabling the output devices also allows the lowest standby noise. To achieve the proper load line, the output impedance of the power amplifier is 300Ω differential. To match this output impedance to a 75Ω load, the transformer must have a turns ratio (voltage ratio) of 2:1 (4:1 impedance ratio). The differential amplifier is biased directly from the +5V supply using the center tap of the output transformer. This provides a significant benefit when switching between transmit mode and transmit-disable mode. Stored energy due to bias currents will cancel within the transformer and prevent switching transients from reaching the load. _______________________________________________________________________________________ 7 MAX3510 Upstream CATV Amplifier Ramp Generator The ramp generator circuit is a simple RC charging circuit, which is used to control power-up and power-down of the output power amplifier. It is made up of CEXT1 and an internal 2kΩ resistor. The choice of CEXT1 is governed by the period of the burst on/off cycle. CEXT1 must be small enough to fully charge/discharge within a burst. A typical value of CEXT1 is 0.0033µF. Serial Interface The serial interface has an active-low enable (CS) to bracket the data, with data clocked in MSB first on the rising edge of SCLK. Data is stored in the storage latch on the rising edge of CS. The serial interface controls the state of the PGA. Tables 2 and 3 show the register format. Serial-interface timing is shown in Figure 2. tions are disabled in this mode and current consumption is reduced to under 2mA. Shutdown Mode In normal operation the shutdown pin (SHDN) is held high. When SHDN and TXEN are taken low, all circuits within the IC are disabled. Only leakage currents flow in this state. Data stored within the serial-data interface latches will be lost upon entering this mode. Current draw is reduced to 1µA (typ) in shutdown mode. G A C B D E F PGA Bias Cell The PGA bias cell is accessed by the SHDN pin. When this pin is taken low, the programmable-gain amplifier and serial data interface are shut off. Note that any gain setting stored in the serial data interface latch will be lost. The power amplifier is unaffected by the PGA Bias cell, therefore TXEN must be held low to be in shutdown mode. This mode lowers supply current draw to less than 1µA typical. D7 D5 D4 D3 D2 D1 D0 E. tSCLKH F. tSENH G. tDATAH/tDATAL A. tSENS B. tSDAS C. tSDAH D. tSCLKL Power Amp Bias Cell The power amp bias cell is used to enable and disable bias to the output differential pair. This is controlled by the TXEN pin (18). D6 Figure 2. Serial-Interface Timing Diagram Functional Modes The MAX3510 has four functional modes controlled through the serial interface or external pins (Table 3): transmit mode, transmit-disable mode, software-shutdown mode, and shutdown mode. Transmit Mode Transmit mode is the normal active mode of the MAX3510. The TXEN pin must be held high in this mode. Note that SHDN must also be held high. Transmit-Disable Mode When in transmit-disable mode, the power amplifier is completely shut off. This mode is activated by taking TXEN low while keeping SHDN high. This mode is typically used between bursts in TDMA systems. Transients are controlled by the action of the transformer balance. Table 2. Serial-Interface Control Word BIT MNEMONIC DESCRIPTION MSB 7 D7 Software Shutdown 6 D6 Test Bit 5 D5 Gain Control, Bit 5 4 D4 Gain Control, Bit 4 3 D3 Gain Control, Bit 3 2 D2 Gain Control, Bit 2 1 D1 Gain Control, Bit 1 LSB 0 D0 Gain Control, Bit 0 Software-Shutdown Mode Software-shutdown mode is enabled when D7 = 0 and TXEN is low. This mode minimizes current consumption while maintaining the programmed gain state stored in the latch of the serial-data interface. All analog func8 _______________________________________________________________________________________ Upstream CATV Amplifier MAX3510 Table 3. Chip-State Control Bits SHDN TXEN D7 D6 D5 D4 D3 D2 D1 D0 GAIN STATE (DECIMAL) 0 0 X X X X X X X X X Shutdown Mode 1 0 0 X X X X X X X X Software-Shutdown Mode 1 0 1 X X X X X X X X Transmit-Disable Mode 1 1 1 X X X X X X X X Transmit Mode 1 1 1 X 0 0 0 0 0 0 0 Gain = -32dB* 1 1 1 X 0 0 0 0 0 1 1 Gain = -31dB* 1 1 1 X — — — — — — — 1 1 1 X 1 0 0 0 0 0 32 1 1 1 X — — — — — — — — 1 1 1 X 1 1 1 1 1 0 62 Gain = 29dB* 1 1 1 X 1 1 1 1 1 1 63 Gain = 30dB* STATE — Gain = 0dB* *Typical gain at +25°C and VCC = +5V Applications Information Output Match The MAX3510’s output circuit is an open-collector differential amplifier. An on-chip resistor across the collectors provides a nominal output impedance of 300Ω in transmit mode and transmit disable mode. Transformer To match the output of the MAX3510 to a 75Ω load, a 2:1 (voltage ratio) transformer is required. This transformer must have adequate bandwidth to cover the intended application. Note that most RF transformers specify bandwidth with a 50Ω source on the primary and a matching resistance on the secondary winding. Operating in a 75Ω system will tend to shift the low-frequency edge of the transformer bandwidth specification up by a factor of 1.5, due to primary inductance. Keep this in mind when specifying a transformer. Bias to the output stage is provided through the center tap on the transformer primary. This greatly diminishes the on/off transients present at the output when switching between transmit and transmit-disable modes. Commercially available transformers typically have adequate balance between half-windings to achieve substantial transient cancellation. Finally, keep in mind that transformer core inductance varies proportionally with temperature. If the application requires low temperature extremes (less than 0°C), adequate primary inductance must be present to sustain low-frequency output capability as temperatures drop. In general this will not be a problem, as modern RF transformers have adequate bandwidth. Input Circuit To achieve rated performance, the input of the MAX3510 must be driven differentially with an appropriate input level. The differential input impedance is approximately 1.5kΩ. Most applications will require a differential lowpass filter preceding the device. The filter design will dictate terminating impedance of a specified value. Place this load impedance across the AC-coupled input pins (see Typical Operating Circuit). The MAX3510 has sufficient gain to produce an output level of 60dBmV (CW through a 2:1 transformer) when driven with a 34dBmV input signal. Rated performance is achieved with this input level. When a lower input level is present, the maximum output level will be reduced proportionally and output linearity will increase. If an input level greater than 34dBmV is used, the 3rd-order distortion performance will degrade slightly. If a single-ended source drives the MAX3510, one of the input terminals must be capacitively coupled to ground (VIN+ or VIN-). The value of this capacitor must be large enough to look like a short circuit at the lowest frequency of interest. For operation at 5MHz with a 75Ω source impedance, a value of 0.1µF will suffice. _______________________________________________________________________________________ 9 MAX3510 Upstream CATV Amplifier VIN+ 2kΩ 1.1pF VIN- Figure 3. Equivalent Input Circuit The model for the MAX3510 input impedance is shown in Figure 3. Layout Issues A well-designed printed circuit board is an essential part of an RF circuit. For best performance pay attention to power-supply layout issues as well the output circuit layout. Power-Supply Layout For minimal coupling between different sections of the IC, the ideal power-supply layout is a star configuration. This configuration has a large-value decoupling capacitor at the central power-supply node. The power-supply traces branch out from this node, each going to a separate power-supply node in the MAX3510 circuit. At the end of each of these traces is a decoupling capacitor that provides a very low impedance at the frequency of interest. This arrangement provides local powersupply decoupling at each power-supply pin. The power supply traces must be made as thick as practical to keep resistance well below 1Ω. Ground inductance degrades distortion performance. Therefore, ground plane connections to GND1 and GND2 should be made with multiple vias if possible. Output Circuit Layout The differential implementation of the MAX3510’s output has the benefit of significantly reducing even-order distortion, the most significant of which is 2nd-harmonic distortion. The degree of distortion cancellation depends on the amplitude and phase balance of the overall circuit. It is critical that the traces that lead from the output pins be exactly the same length. 10 ______________________________________________________________________________________ Upstream CATV Amplifier Chip Information TRANSISTOR COUNT: 736 TOP VIEW GND 1 20 GND2 VCC1 2 19 VCC2 GND 3 18 TXEN GND1 4 VIN+ 5 17 CEXT1 MAX3510 VIN- 6 16 VOUT+ 15 VOUT- GND 7 14 CEXT2 CS 8 13 N.C. SDA 9 12 SHDN SCLK 10 11 GND QSOP ______________________________________________________________________________________ 11 MAX3510 Pin Configuration Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) QSOP.EPS MAX3510 Upstream CATV Amplifier Revision History Pages changed at Rev 4: 1, 2, 12 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. 12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.