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19-2351; Rev 0; 4/02
KIT ATION EVALU ABLE AVAIL
Upstream CATV Amplifier
General Description Features
o Single 5V Supply Operation o Accurate Gain Control, 1dB over 56dB Range o Gain Programmable in 0.5dB Steps o -55dBc Harmonic Distortion at 65MHz o Low Burst On/Off Transient
MAX3505
The MAX3505 programmable power amplifier is designed for use in CATV upstream applications. The MAX3505 drives 64dBmV (QPSK) into a 75 load when driven with a 34dBmV nominal input signal. Both input and output ports are differential, requiring that an external balun be used at the output port. The variable gain feature provides greater than 56dB of dynamic range, which is controlled by an SPITM 3-wire interface. Gain control is available in 0.5dB steps. The device operates over a frequency range of 5MHz to 65MHz. The MAX3505 is internally matched for use with a 1:1 balun. This device operates from a single 5VDC supply and draws 285mA during transmit (100% duty cycle, 64dBmV out). The bias current is automatically adjusted based on the output level to increase efficiency. Additionally, the device can be disabled between bursts to minimize noise and save power while still maintaining a match at the output port. In addition, a shutdown mode is available to disable all circuitry and reduce current consumption to 5A (typ). The MAX3505 is available in a 20-pin QFN package. The device operates in the extended industrial temperature range (-40C to +85C).
Ordering Information
PART MAX3505EGP TEMP RANGE -40C to +85C PIN-PACKAGE 20 QFN-EP* (5mm x 5mm)
*EP = exposed pad
Applications
DOCSIS/EuroDOCSIS and DVB Cable Modems OpenCable Set-Top Box Telephony Over Cable
SPI is a trademark of Motorola, Inc. DOCSIS/EuroDOCSIS/OpenCable are trademarks of CableLabs. TOP VIEW
CEXT 16 N.C. N.C. N.C. 18 N.C. 17
Pin Configuration
CATV Status Monitor
20 VCC IN+ 1 2 3 4 5
Typical Operating Circuit
10 CONTROL LOGIC 0.001F + INPUT 0.001F +5V 0.1F 1 4 VCC GND GND SDA SCLK CS 7 8 CONTROL LOGIC CEXT 16 ANTI-ALIAS FILTER 4 2 IN+ 5V SHDN 9 TXEN VCC OUT+ 15 14 0.1F 5V 1:1 OUTPUT
19
15 14 13
VCC OUT+ N.C. OUTN.C.
GND INGND
MAX3505
12 11 10 SHDN
MAX3505
IN-
6
7
8
CS
0.1F
5 6
SCLK
QFN**
**NOTE: THE EXPOSED PAD MUST BE SOLDERED TO GROUND.
________________________________________________________________ Maxim Integrated Products
TXEN
SDA
0.1F
9
OUT-
12
1
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.
Upstream CATV Amplifier MAX3505
ABSOLUTE MAXIMUM RATINGS
VCC, OUT+, OUT-..................................................-0.5V to +6.5V Input Voltage Levels (all inputs) .................-0.3V to (VCC + 0.3V) Continuous Input Voltage (IN+, IN-)....................................2VP-P Continuous Current (OUT+, OUT-) ...................................175mA Continuous Power Dissipation (TA = +85C) 20-Pin QFN (derate 27mW/C above +85C) .............1800mW Operating Temperature Range .......................... -40C to +85C Junction Temperature ..................................................... +150C Storage Temperature Range ............................ -65C to +150C Lead Temperature (soldering, 10s) ................................ +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
(MAX3505EV kit; VCC = 4.75V to 5.25V, VGND = 0V, TXEN = SHDN = high, TA = -40C to +85C. Typical parameters are at VCC = 5.0V, TA = +25C, unless otherwise specified.) (Note1)
PARAMETER Supply Voltage Supply-Current Transmit Mode Supply-Current Transmit Disable Mode Supply-Current Low-Power Standby LOGIC INPUTS Input High Voltage Input Low Voltage Input High Current Input Low Current VINH VINL IBIASH IBIASL VINH = 3.3V VINL = 0V -100 2.0 0.8 100 V V A A SYMBOL VCC ICC ICC ICC D7 = 1, gain code = 123 (Av = 31dB) D7 = 0, gain code = 92 (Av = 0dB) TXEN = low SHDN = low CONDITIONS MIN 4.75 285 55 4.8 5 7 TYP MAX 5.25 335 UNITS V mA mA A
AC ELECTRICAL CHARACTERISTICS
(MAX3505 EV kit; VCC = 4.75V to 5.25V, VGND = 0V, PIN = 34dBmV, TXEN = SHDN = high, TA = -40C to +85C. Typical parameters are at TA =+25C, unless otherwise specified.) (Note 1)
PARAMETER SYMBOL CONDITIONS D7 = 1, gain code = 123, TA = 0C to +85C D7 = 1, gain code = 119, TA = 0C to +85C D7 = 1, gain code = 99, TA = 0C to +85C Voltage Gain, fIN = 5MHz AV D7 = 1, gain code = 82, TA = 0C to +85C D7 = 0, gain code = 112, TA = 0C to +85C D7 = 0, gain code = 92, TA = 0C to +85C D7 = 0, gain code = 72, TA = 0C to +85C D7 = 0, gain code = 43, TA = 0C to +85C MIN 29.5 27.5 17.5 9 8 -2 -12 -26.5 TYP 31 29 19 10.5 9.5 -0.5 -10.5 -25.0 MAX 32.5 30.5 20.5 12 11 +1 -9 -23.5 dB UNITS
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Upstream CATV Amplifier
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX3505 EV kit; VCC = 4.75V to 5.25V, VGND = 0V, PIN = 34dBmV, TXEN = SHDN = high, TA = -40C to +85C. Typical parameters are at VCC = 5.0V, TA = +25C, unless otherwise specified.) (Note1)
PARAMETER Voltage Gain, fIN = 65MHz SYMBOL AV CONDITIONS D7 = 1, gain code = 125, TA = -40C to +85C (Note 2) VOUT = 64dBmV, fIN = 5MHz to 42MHz (Note 2) Gain Rolloff VOUT = 64dBmV, fIN = 5MHz to 65MHz (Note 2) fIN = 5MHz to 65MHz, AV = -26dB to +27dB Gain Step Size fIN = 5MHz to 65MHz, AV = -26dB to +27dB; any 2-bit transition of D0, D1 fIN = 5MHz to 65MHz, D7 = 0, gain code = 112; to D7 = 1, gain code = 82 Transmit-Disable Mode Noise Isolation in Transmit-Disable Mode Transmit Mode Noise Transmit Enable Transient Duration Transmit Disable Transient Duration Transmit Disable/ Transmit Enable Transient Step Size Input Impedance Output Return Loss Output Return Loss in TransmitDisable Mode ZIN TXEN = low, BW = 160kHz, fIN = 5MHz to 65MHz (Note 2) TXEN = low, fIN = 5MHz to 65MHz (Note 2) BW = 160kHz, fIN = 5MHz to 65MHz, AV = -26dB to +30dB (Note 2) TXEN input rise/fall time < 0.1s (Note 2) TXEN input rise/fall time < 0.1s (Note 2) D7 = 1, gain code = 119 (AV = 29dB) D7 = 1, gain code = 83 (AV = 11dB) D7 = 0, gain code = 92 (AV = -0.5dB) fIN = 5MHz to 65MHz, differential (Note 2) fIN = 5MHz to 65MHz, in 75 system, D7 = 1, gain code = 119 (AV = 27dB) fIN = 5MHz to 65MHz, in 75 system, TXEN = low 3 2 10 10 k dB dB 30 60 -55 2 2 80 20 mVP-P 0.7 0.65 -0.85 0.5 1.0 1.0 1.3 1.35 -65 dBmV dB dBc s s dB -1.35 MIN 29.0 -0.5 -0.85 dB TYP MAX UNITS dB
MAX3505
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Upstream CATV Amplifier MAX3505
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX3505 EV kit; VCC = 4.75V to 5.25V, VGND = 0V, PIN = 34dBmV, TXEN = SHDN = high, TA = -40C to +85C. Typical parameters are at TA =+25C, unless otherwise specified.) (Note 1)
PARAMETER SYMBOL CONDITIONS Input tones at 42MHz and 42.2MHz, both 31dBmV, VOUT = 60dBmV/tone (Note 2) Input tones at 65MHz and 65.2MHz, both 31dBmV, VOUT = 60dBmV/tone 2nd Harmonic Distortion 3rd Harmonic Distortion HD2 HD3 fIN = 33MHz, VOUT = 64dBmV fIN = 65MHz, VOUT = 64dBmV (Note 2) fIN = 22MHz, VOUT = 64dBmV fIN = 65MHz, VOUT = 64dBmV MIN TYP -53 -47 -55 -55 -55 -55 -50 -50 -50 -48.5 dBc dBc MAX -47 dBc UNITS
Two-Tone Third-Order Distortion
IM3
TIMING CHARACTERISTICS
(VCC = 4.75V to 5.25V, VGND = 0V, TXEN = SHDN = high, TA = +25C, D7 = 1, unless otherwise specified.)
PARAMETER SEN to SCLK Rise Set Time SEN to SCLK Rise Hold Time SDA to SCLK Setup Time SDA to SCLK Hold Time SDA Pulse-Width High SDA Pulse-Width Low SCLK Pulse-Width High SCLK Pulse-Width Low SYMBOL tSENS tSENH tSDAS tSDAH TDATAH TDATAL tSCLKH tSCLKL CONDITIONS MIN 20 10 10 20 50 50 50 50 TYP MAX UNITS ns ns ns ns ns ns ns ns
Note 1: All parameters are guaranteed by design and characterization to 3 sigma for TA < +25C, unless otherwise specified. Note 2: Guaranteed by design and characterization to 6 sigma.
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Upstream CATV Amplifier
Typical Operating Characteristics
(Typical applications circuit; VCC = 5V, VIN = 34dBmV, TXEN = SHDN = high, fIN = 20MHz, ZLOAD = 75, TA = +25C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
MAX3505 toc01
MAX3505
SUPPLY CURRENT vs. GAIN CODE
MAX3505 toc02
VOLTAGE GAIN vs. SUPPLY VOLTAGE HIGH-POWER MODE
GAIN CODE = 123 31.5 +25C VOLTAGE GAIN (dB) 31.0 30.5 +85C 30.0 29.5 29.0 -40C
MAX3505 toc03
350 300 SUPPLY CURRENT (mA) 250 200 150 100 50 TRANSMIT-DISABLE MODE 0 -50 -25 0 25 50 75 TRANSMIT-ENABLE MODE, LOW NOISE, GAIN CODE = 92 TRANSMIT-ENABLE MODE, HIGH POWER, GAIN CODE = 123
400 350 SUPPLY CURRENT (mA) 300 250 200 150 100 LOW-NOISE MODE 50 0 HIGH-POWER MODE
32.0
100
0
20
40
60
80
100
120
140
4.7
4.8
4.9
5.0
5.1
5.2
5.3
TEMPERATURE (C)
GAIN CODE
SUPPLY VOLTAGE (V)
VOLTAGE GAIN vs. SUPPLY VOLTAGE LOW-POWER MODE
MAX3505 toc04
VOLTAGE GAIN vs. TEMPERATURE HIGH-POWER MODE
MAX3505 toc05
VOLTAGE GAIN vs. TEMPERATURE LOW-NOISE MODE
GAIN CODE = 72 -9.5 VOLTAGE GAIN (dB) -10.0 -10.5 -11.0 -11.5 -12.0 VCC = 4.75V VCC = 5V VCC = 5.25V
MAX3505 toc06
-23.0 GAIN CODE = 43 -23.5 VOLTAGE GAIN (dB) -24.0 -24.5 -25.0 -25.5 -26.0 4.7 4.8 4.9 5.0 5.1 5.2 +85C +25C -40C
32.0 GAIN CODE = 123 31.5 VOLTAGE GAIN (dB) 31.0 30.5 30.0 29.5 29.0 VCC = 4.75V VCC = 5V
-9.0
VCC = 5.25V
5.3
-40
-15
10
35
60
85
-40
-15
10
35
60
85
SUPPLY VOLTAGE (V)
TEMPERATURE (C)
TEMPERATURE (C)
VOLTAGE GAIN vs. FREQUENCY HIGH-POWER MODE
30 25 VOLTAGE GAIN (dB) 20 15 10 5 0 -5 -10 -15 1 10 100 1000 FREQUENCY (MHz) GAIN CODE A = 123, B = 99, C = 82, D = 62 D -30 -40 1 B C
MAX3505 toc07
VOLTAGE GAIN vs. FREQUENCY LOW-NOISE MODE
MAX3505 toc08
VOLTAGE GAIN vs. GAIN CODE
35 30 25 20 15 10 5 0 -5 -10 -15 -20 -25 -30 -35 30 40
MAX3505 toc09
35 A
20 10 VOLTAGE GAIN (dB) 0 -10 -20 GAIN CODE A = 112, B = 92, C = 72, D = 43 10 100 A B C
HIGH-POWER MODE
VOLTAGE GAIN (dB)
LOW-NOISE MODE
D
1000
50 60 70
80 90 100 110 120
FREQUENCY (MHz)
GAIN CODE
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Upstream CATV Amplifier MAX3505
Typical Operating Characteristics (continued)
(Typical applications circuit; VCC = 5V, VIN = 34dBmV, TXEN = SHDN = high, fIN = 20MHz, ZLOAD = 75, TA = +25C, unless otherwise noted.)
GAIN STEP vs. GAIN CODE HIGH-POWER MODE
MAX3505 toc10
GAIN STEP vs. GAIN CODE LOW-NOISE MODE
MAX3505 toc11
TRANSMIT NOISE vs. GAIN CODE
MAX3505 toc12
1.0 0.9 0.8 GAIN STEP (dB) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 60 70 80 90 100 110 120 GAIN CODE
1.0 0.9 0.8 GAIN STEP (dB) 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 30 40 50 60 70 80
-20 OUTPUT NOISE (dBmV IN 160kHz) -25 HIGH-POWER MODE -30 -35 -40 -45 -50 -55
LOW-NOISE MODE
90 100 110 120
30
50
70
90
110
130
GAIN CODE
GAIN CODE
2ND HARMONIC DISTORTION vs. INPUT FREQUENCY
MAX3505 toc13
3RD HARMONIC DISTORTION vs. INPUT FREQUENCY
MAX3505 toc14
POWER-UP/DOWN TRANSIENTS vs. GAIN CODE
MAX3505 toc15
-50 2ND HARMONIC DISTORTION (dBc) -55 -60 -65 -70 -75 -80 -85 -90 -95 0 10 20 30 40 50 60 6dBmV, LN 50dBmV, HP 20dBmV, LN 64dBmV, HP
-50 3RD HARMONIC DISTORTION (dBc) -55 -60 -65 -70 6dBmV, LN -75 -80 -85 -90 64dBmV, HP 50dBmV, HP 20dBmV, LN
100
TRANSIENT LEVEL (mVP-P)
10
HIGH-POWER MODE 1
LOW-NOISE MODE 0 10 50 40 INPUT FREQUENCY (MHz) 20 30 60 70 0.1 0 20 40 60 80 100 120 140 GAIN CODE
70
INPUT FREQUENCY (MHz)
OUTPUT RETURN LOSS vs. FREQUENCY (75 SYSTEM)
MAX3505 toc16
OUTPUT IMPEDANCE (75 SYSTEM)
MAX3505 toc17
OUTPUT SPECTRUM
-10 -20 -30 -40 (dB) -50 -60 VOUT = 61dBmV = 0.25 1280ksps
MAX3505 toc18
0 -5 OUTPUT RETURN LOSS (dB) -10 -15 -20 -25 -30 1 10 FREQUENCY (MHz) HIGH-POWER MODE
0
LOW-NOISE MODE/ TRANSMITDISABLE MODE
LOW-NOISE MODE/ TRANSMIT-DISABLE MODE
HIGH-POWER MODE
-70 -80 -90 -100
100
500kHz/div
6
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Upstream CATV Amplifier
Typical Operating Characteristics (continued)
(Typical applications circuit; VCC = 5V, VIN = 34dBmV, TXEN = SHDN = high, fIN = 20MHz, ZLOAD = 75, TA = +25C, unless otherwise noted.)
OUTPUT SPECTRUM
MAX3505 toc19
MAX3505
OUTPUT SPECTRUM
-10 -20 -30 -40 (dB) -50 -60 -70 -80 -90 -100 VOUT = 61dBmV = 0.25 1280ksps
MAX3505 toc20
0 -10 -20 -30 -40 (dB) -50 -60 -70 -80 -90 -100 100kHz/div VOUT = 61dBmV = 0.25 160ksps
0
6MHz/div
Pin Description
PIN 1 2 3 4 5 6 7 8 9 10 11,13,17-20 12 14 15 16 Exposed Pad NAME VCC IN+ GND INGND SDA SCLK CS TXEN SHDN N.C. OUTOUT+ VCC CEXT GND FUNCTION Programmable-Gain Amplifier (PGA) +5V Supply. Bypass to GND with a 0.1F decoupling capacitor as close to the part as possible. Positive PGA Input. Along with IN-, this port forms a high-impedance differential input to the PGA. Driving this port differentially increases the rejection of second-order distortion at low output levels. PGA RF Ground. As with all ground connections, maintain the shortest possible (low-inductance) length to the ground plane. Negative PGA Input. When not used, this port must be AC-coupled to ground. See IN+. Ground Serial-Interface Data. TTL-compatible input. See the Serial Interface section. Serial-Interface Clock. TTL-compatible input. See the Serial Interface section. Serial-Interface Enable. TTL-compatible input. See the Serial Interface section. Transmit Enable. Drive TXEN high to place the device in transmit-enable mode. Shutdown. When SHDN is set low, all functions (including the serial interface) are disabled. No Connection Negative Output. Along with OUT+, this port forms a 75 impedance output. This port is matched to a 75 load using a 1:1 transformer. Positive Output. See OUT-. Output Amplifier Bias, +5V Supply. Bypass to GND with a 0.1F decoupling capacitor as close to the part as possible. RF Output Bypass. Bypass to GND with a 0.1F capacitor. Ground
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Upstream CATV Amplifier MAX3505
Functional Diagram
TXEN SHDN VCC
BIAS CONTROL
MAX3505
HIGH POWER OUTCEXT
IN+ OUT+
INLOW NOISE
D/A CONVERTER
SERIAL DATA INTERFACE
CS SDA SCLK
GND
Detailed Description
Programmable-Gain Amplifier
The PGA consists of the variable-gain amplifier (VGA) and the digital-to-analog converter (DAC), which provide better than 56dB of output-level control in 0.5dB steps. The PGA is implemented as a programmable Gilbert-cell attenuator. The gain of the PGA is determined by a 7-bit word (D6-D0) programmed through the serial data interface (Tables 1 and 2). Specified performance is achieved when the input is driven differentially. The device can be driven single ended. 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 lowimpedance path to ground at the lowest frequency of operation. For operation down to 5MHz, a 0.001F capacitor is suggested.
mode, the output amplifiers are powered down. A 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 results in low output noise. To match the output impedance to a 75 load, the transformer must have a turns ratio of 1:1. 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 within the transformer cancels and prevents switching transients from reaching the load.
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 and the output amplifiers. Tables 1 and 2 show the register format. Serial-interface timing is shown in Figure 1.
Output Amplifiers
The output amplifiers are class A differential amplifiers, capable of driving +64dBmV (QPSK) 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
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Upstream CATV Amplifier
Applications Information
High-Power and Low-Noise Modes
The MAX3505 has two transmit modes, high power (HP) and low noise (LN). Each of these modes is actuated by the high-order bit, D7, of the 8-bit programming word. When D7 is a logic 1, HP mode is enabled. When D7 is a logic 0, LN mode is enabled. Each of these modes is characterized by the activation of a distinct output stage. In HP mode, the output stage exhibits 16dB higher gain than LN mode. The lower gain of the LN output stage allows for significantly lower output noise and lower transmit-enable/transmit-disable transients. The full range of gain codes (D6-D0) can be used in either mode. For DOCSIS applications, HP mode is recommended for output levels at or above 34.5dBmV (D7 = 1, gain code = 82), LN mode when the output level is below +33.5dBmV (D7 = 0, gain code = 112).
A G B C D E F
MAX3505
D7
D6 A. tSENS B. tSDAS C. tSDAH D. tSCKL
D5
D4
D3
D2
D1
D0
E. tSCKH F. tSENH G. tDATAH/tDATAL
Figure1. Serial-Interface Timing Diagram
Shutdown Mode
In normal operation, the shutdown pin (SHDN) is held high. When SHDN is taken low, all circuits within the IC are disabled. Only leakage currents flow in this state. Data stored within the serial-data interface latches is lost upon entering this mode. Current consumption is reduced to 5A (typ) in shutdown mode.
Table 1. Serial-Interface Control Word
BIT MSB 7 6 5 4 3 2 1 LSB 0 MNEMONIC D7 D6 D5 D4 D3 D2 D1 D0 DESCRIPTION High-power/low-noise mode select Gain code, bit 6 Gain code, bit 5 Gain code, bit 4 Gain code, bit 3 Gain code, bit 2 Gain code, bit 1 Gain code, bit 0
Transformer
A transformer is required at the output of the MAX3505 to convert from differential to single-ended drive. This transformer must have adequate bandwidth to cover the intended application. Note that most RF transformers specify bandwidth with a 50 source on the primary and a matching resistance on the secondary winding. Operating in a 75 system tends 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 0C), adequate primary inductance must be present to sustain low-frequency output capability as temperatures drop. In general, this is not a problem, as modern RF transformers have adequate bandwidth.
Input Circuit
To achieve rated performance, drive the inputs of the MAX3505 differentially with an appropriate input level. The differential input impedance is approximately 2k. Most applications require a differential lowpass filter preceding the device. The filter design dictates a terminating impedance of a specified value. Place this load impedance across the AC-coupled input pins (see the Typical Operating Circuit). The MAX3505 has sufficient gain to produce an output level of 64dBmV (QPSK) when driven with a +34dBmV input signal. When a lower input level is present, the maximum output level is reduced proportionally and output linearity increases. If an input level greater than +34dBmV is used, the 3rd-order distortion performance degrades slightly.
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Upstream CATV Amplifier MAX3505
Table 2. Chip-State Control Bits
SHDN 0 1 1 1 1 1 1 1 1 1 TXEN X 0 1 1 1 1 1 1 1 1 D7 X X 1 0 0 0 0 1 1 1 D6 X X X X 0 1 1 1 1 1 D5 X X X X 1 0 1 0 1 1 D4 X X X X 0 1 1 1 0 1 D3 X X X X 1 1 0 0 0 1 D2 X X X X 0 1 0 0 0 0 D1 X X X X 1 0 0 1 1 1 D0 X X X X 1 0 0 0 1 1 43 92 112 82 99 123 GAIN CODE (DECIMAL) STATES Shutdown Mode Transmit-Disable Mode Transmit-Enable Mode, High Power Transmit-Enable Mode, Low Noise AV = -25.0dB* AV = -0.5dB* AV = 9.5dB* AV = 10.5dB* AV = 19.0dB* AV = 31.0dB*
*Typical gain at +25C, VCC = 5.0V. If single-ended sources drive the MAX3505, one of the input terminals must be capacitively coupled to ground (IN+ or IN-). 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 75 source impedance, a value of 0.001F suffices. The power-supply traces must be made as thick as practical. Ground inductance degrades distortion performance. Therefore, ground plane connections should be made with multiple vias.
Exposed-Paddle Thermal Considerations
The MAX3505's 20-pin QFN package provides a low thermal-resistance path to the die. It is important that the PC board on which the MAX3505 is mounted be designed to conduct heat from this contact. In addition, the EP should be provided with a low-inductance path to electrical ground. It is recommended that the EP be soldered to a ground plane on the PC board, either directly or through an array of plated via holes.
Layout Issues
A well-designed printed circuit (PC) 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.
Output Circuit Layout
The differential implementation of the MAX3505'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 important to keep the trace lengths from the output pins equal.
Chip Information
TRANSISTOR COUNT: 1180 SUBSTRATE CONNECTED TO GND
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 circuit. At the end of each of these traces is a decoupling capacitor that provides very low impedance at the frequency of interest. This arrangement provides local power-supply decoupling at each power-supply pin.
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Upstream CATV Amplifier
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.)
MAX3505
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Upstream CATV Amplifier MAX3505
Package Information (continued)
(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.)
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 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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