MAXIM MAX3509

19-1700; Rev 0; 4/00
UAL
IT MAN
TION K
A
ET
U
E
L
H
A
S
EV
TA
WS DA
FOLLO
Upstream CATV Amplifier
Features
♦ Ultra-Low Power-Up/Down Transients,
25mV (typ) at 66dBmV Output
The MAX3509 offers a transmit-disable mode, which
places the device in a high-isolation state for use
between bursts in TDMA systems. In this mode, all analog functions are shut down, minimizing output noise
and power consumption. When entering and leaving
transmit-disable mode, transients are kept to 25mV
nominal at full gain. In addition, supply current is reduced to 7.8mA.
♦ Gain Programmable in 1dB Steps
An additional power-down mode is available. Shutdown
mode disables all circuitry and reduces current consumption to less than 1µA.
The MAX3509 is available in a 20-pin TSSOP-EP package for the extended-industrial temperature range
(-40°C to +85°C).
♦ Single-Supply Operation
♦ Output Level Ranges from <12dBmV to 67dBmV
(QPSK)
♦ Low Transmit Output Noise Floor: -41dBmV
(160kHz BW)
♦ Low Transmit-Disable Output Noise: -70dBmV
♦ Shutdown Mode
Ordering Information
PART
MAX3509EUP
TEMP. RANGE
PIN-PACKAGE
-40°C to +85°C
20 TSSOP-EP*
*Exposed paddle
Applications
Telephony over Cable
OPENCATV Set-Top Box
CATV Status Monitor
CATV Infrastructure
Cable Modems
Pin Configuration
Typical Operating Circuit
3
IN
ANTI-ALIAS FILTER
+9V
0.1µF
4
1000pF
1000pF
+9V
0.1µF
LOGIC
INPUTS
*EXPOSED PADDLE
5
6
8
7
2
1
20
19
18
VCC2 17
VCC1
TOP VIEW
+9V
0.1µF
GND1
MAX3509
IN+
IN-
VCC1
GND1
SHDN
TXEN
SCLK
SDA
CS
OUT+
OUTVCC2
4700pF
16
OUT
14
20 SCLK
SHDN 2
19 SDA
VCC1 3
18 CS
GND1 4
T1
1:1
4700pF
15
TXEN 1
IN+ 5
+9V
0.1µF
GND2 *
9
GND
10
GND
11
GND
12
GND
13
GND
17 VCC2
MAX3509
16 OUT+
IN- 6
15 OUT-
GND1 7
14 VCC2
VCC1 8
13 GND
GND 9
12 GND
GND 10
EXPOSED PADDLE
11 GND
TSSOP-EP
†Covered
by U.S. Patent numbers 5,748,027 and 5,994,955.
________________________________________________________________ Maxim Integrated Products
1
For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
MAX3509†
General Description
The MAX3509 is a programmable power amplifier for
use in CATV upstream applications. The device outputs
up to 66dBmV QPSK through a 1:1 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 5MHz to 65MHz frequency range.
MAX3509
Upstream CATV Amplifier
ABSOLUTE MAXIMUM RATINGS
VCC1, VCC2 to GND, GND1 .................................-0.3V to +10.0V
SCLK, SDA, CS, TXEN, SHDN to GND
and GND1 .........................................................-0.3V to +5.5V
Continuous Input Voltage (IN+, IN-) ...................................2Vp-p
Continuous Current (OUT+, OUT-) .....................................80mA
Continuous Power Dissipation (TA = +70°C)
20-Pin TSSOP-EP (derate at 27mW/°C above
+70°C)........................................................................2200mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +150°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
(VCC1 = VCC2 = 8.5V to 9.5V, 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
CONDITIONS
Supply Voltage
VCC
Supply Current Transmit Mode
ICC
Supply Current Transmit-Disable
Mode
ICC
TXEN = low or D7 = 0
Supply Current Shutdown Mode
ICC
SHDN = low, TXEN = low
Input High Voltage
VINH
Input Low Voltage
VINL
Input High Current
IBIASH
Input Low Current
IBIASL
MIN
TYP
8.5
MAX
UNITS
9.5
V
84
115
mA
7.8
10
mA
1
10
µA
2.0
V
0.8
V
100
µA
-100
µA
AC ELECTRICAL CHARACTERISTICS
(MAX3509 EV kit, VCC1 = VCC2 = 8.5V to 9.5V, TXEN = SHDN = high, D7 = 1, VINPUT = 34dBmV differential, output impedance =
75Ω through a 1:1 transformer, TA = -40°C to +85°C, unless otherwise noted. Typical parameters are at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
TA = +25°C, fINPUT = 42MHz, gain control
word = 63
Voltage Gain
AV
Gain Step Size
TA = +25°C, fINPUT = 42MHz, gain control
word = 0
-22
TA = +25°C, fINPUT = 42MHz, gain control
word = 50
22
24
2
25.9
dB
31
fINPUT = 42MHz, gain control word = 0
-21
fINPUT = 42MHz, gain control word = 50
20.2
24
25.9
VOUTPUT = 60dBmV, fINPUT = 5MHz to 42MHz
(Note 1)
0.1
0.4
VOUTPUT = 60dBmV, fINPUT = 5MHz to 65MHz
(Note 1)
0.3
0.9
1
1.3
fINPUT = 5MHz to 65MHz, AV = -20dB to
+33dB
UNITS
33
fINPUT = 42MHz, gain control word = 63
Gain Flatness
MAX
dB
0.7
_______________________________________________________________________________________
dB
Upstream CATV Amplifier
(MAX3509 EV kit, VCC1 = VCC2 = 8.5V to 9.5V, TXEN = SHDN = high, D7 = 1, VINPUT = 34dBmV differential, output impedance =
75Ω through a 1:1 transformer, TA = -40°C to +85°C, unless otherwise noted. Typical parameters are at TA = +25°C.)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
-85
dBc
-41
-39.5
BW = 160kHz, AV = 32dB (Note 1)
BW = 160kHz, AV = -20dB, TA = +25°C (Note 1)
Transmit Mode Noise
BW = 160kHz, AV = -20dB, TA = +85°C (Note 1)
-38.5
dBmV
Transmit-Disable Mode Noise
Floor
TXEN = low, BW = 160kHz, AV = +32dB,
fINPUT = 5MHz to 65MHz (Note 1)
TXEN Enable Transient Duration
TXEN rise time <0.1µs, TA = +25°C (Note 1)
TXEN Disable Transient Duration
TXEN fall time <0.1µs, TA = +25°C (Note 1)
AV = 32dB, TA = +25°C (Note 1)
AV = 2dB or lower, TA = +25°C (Note 1)
1.5
9
fINPUT = 5MHz to 65MHz, single ended,
TA = +25°C (Note 1)
1.2
kΩ
TXEN Transient Step Size
ZINPUT
Input Impedance
-70
dBmV
2
µs
1
1.5
µs
25
100
1.4
mVp-p
Output Impedance in Transmit
Mode
ZOUTPUT fINPUT = 5MHz to 65MHz, TA = +25°C (Note 1)
1.2
Ω
Output Impedance in
Transmit-Disable Mode
TXEN = low, fINPUT = 5MHz to 65MHz,
ZOUTPUT T = +25°C (Note 1)
A
170
Ω
-53
dBc
Two-Tone Third-Order Distortion
IM3
Input tones at 65MHz and 65.2MHz,
VINPUT = 31dBmV/tone, AV = 32dB (Note 1)
fINPUT = 33MHz
2nd Harmonic Distortion
HD2
fINPUT = 65MHz
(Note 1)
fINPUT = 22MHz
3rd Harmonic Distortion
HD3
fINPUT = 65MHz
(Note 1)
Output 1dB Compression Point
P1dB
VOUTPUT = +60dBmV
-56
-53
VOUTPUT = +66dBmV
-56
-50
VOUTPUT = 66dBmV
-56
-50
VOUTPUT = +60dBmV
-56
-53
VOUTPUT = +66dBmV
-53
-48.5
VOUTPUT = 66dBmV
-43
-40
dBc
dBc
AV = 32dB, 65MHz (Note 1)
26
dBm
AM to AM
AM/AM
AV = 32dB, VINPUT swept from 34dBmV to
38dBmV (Note 1)
0.1
dB
AM to PM
AM/PM
AV = 32dB, VINPUT swept from 34dBmV to
38dBmV (Note 1)
1.7
degrees
_______________________________________________________________________________________
3
MAX3509
AC ELECTRICAL CHARACTERISTICS (continued)
TIMING CHARACTERISTICS
(VCC1 = VCC2 = 8.5V to 9.5V, TXEN = SHDN = high, D7 = 1, TA = +25°C, unless otherwise noted.) (Note 1)
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.
Typical Operating Characteristics
(MAX3509 EV kit, VCC1 = VCC2 = +9V, VIN = +34dBmV, TXEN = SHDN = high, D7 = 1, fINPUT = 10MHz, ZLOAD = 75Ω through a 1:1
transformer, TA = +25°C, unless otherwise noted.)
SUPPLY CURRENT vs. TEMPERATURE
TRANSMIT DISABLE
85
80
75
8.0
7.5
7.0
70
6.5
65
-40
-15
10
35
-15
10
35
60
VOLTAGE GAIN vs. SUPPLY VOLTAGE
(CONTROL WORD = 25)
VOLTAGE GAIN vs. SUPPLY VOLTAGE
(CONTROL WORD = 50)
0.26
TA = -40°C
0.24
TA = +85°C
24.6
TA = +25°C
TA = +25°C
0.22
24.2
0.20
24.0
36
42
48
54
60
66
72
VOLTAGE GAIN vs. TEMPERATURE
(CONTROL WORD = 25)
24.8
24.4
90
OUTPUT POWER (dBmV)
0.5
8.5V
0.4
0.3
VOLTAGE GAIN (dB)
VOLTAGE GAIN (dB)
0.28
TA = -40°C
100
30
MAX3509-05
MAX3509-04
25.2
25.0
TA = +25°C
85
TEMPERATURE (°C)
TA = +85°C
TA = +85°C
110
70
-40
85
TEMPERATURE (°C)
0.32
0.30
60
120
80
6.0
60
MAX3509-03
130
SUPPLY CURRENT (mA)
8.5
SUPPLY CURRENT (mA)
90
140
MAX3509-02
95
SUPPLY CURRENT (mA)
9.0
MAX3509-01
100
SUPPLY CURRENT
vs. OUTPUT POWER
MAX3509-06
SUPPLY CURRENT vs. TEMPERATURE
TRANSMIT ENABLE
VOLTAGE GAIN (dB)
MAX3509
Upstream CATV Amplifier
0.2
0.1
9.5V
9.0V
0
-0.1
-0.2
-0.3
TA = -40°C
-0.4
4
-0.5
8.5 8.6 8.7 8.8 8.9 9.0 9.1 9.2 9.3 9.4 9.5
8.5 8.6 8.7 8.8 8.9 9.0 9.1 9.2 9.3 9.4 9.5
SUPPLY VOLTAGE (V)
SUPPLY VOLTAGE (V)
-40
-15
10
35
TEMPERATURE (°C)
_______________________________________________________________________________________
60
85
Upstream CATV Amplifier
VOLTAGE GAIN
vs. CONTROL WORD
E
F
G
5
60MHz
0
-30
100
0.7
0
500
1.0
0.8
-20
10
1.1
0.9
10
20
30
40
50
60
0
10
20
30
40
50
60
FREQUENCY (MHz)
CONTROL WORD (DECIMAL)
CONTROL WORD (DECIMAL)
TRANSMIT OUTPUT NOISE vs. GAIN
POWER-UP/DOWN TRANSIENTS
vs. CONTROL WORD
2ND HARMONIC DISTORTION
vs. INPUT FREQUENCY
-24
TRANSIENT LEVEL (mVp-p)
-26
-28
-30
-32
-34
-36
-38
10
-58
MAX3509-12
-22
2ND HARMONIC DISTORTION (dBc)
100
MAX3509-10
-20
MAX3509-11
-50
10
-10
GAIN CONTROL WORD
A = 63, B = 57, C = 48,
D = 36, E = 24, F = 12,
G=6
-40
20
GAIN STEP (dB)
VOLTAGE GAIN (dB)
VOLTAGE GAIN (dB)
0
-10
-20
1.2
10MHz
D
-30
OUTPUT NOISE (dBmV IN 160kHz)
30
C
20
10
1.3
MAX3509-08
A
B
30
40
MAX3509-07
50
40
GAIN STEP
vs. CONTROL WORD
MAX3509-09
VOLTAGE GAIN vs. FREQUENCY
66dBmV
-62
60dBmV
-66
-70
-40
-14
-4
6
16
26
36
0
10
20
30
40
50
60
0
70
GAIN (dB)
CONTROL WORD
2ND HARMONIC DISTORTION
vs. INPUT FREQUENCY
3RD HARMONIC DISTORTION vs.
INPUT FREQUENCY AND OUTPUT POWER
10dBmV
-60
30dBmV
-65
-70
-75
MAX3509-14
-55
66dBmV
-45
-50
0
10
20
30
40
50
FREQUENCY (MHz)
60
70
20
30
40
50
60
70
QPSK OUTPUT SPECTRUM
-10
-20
-30
60dBmV
VOUT = 66dBmV
1280 ks/s
α = 0.25
-40
-55
-60
-50
30dBmV
-60
-65
-70
-70
10dBmV
-75
-80
-80
-90
-85
-100
-90
-80
10
FREQUENCY (MHz)
-40
3RD HARMONIC DISTORTION (dBc)
MAX3509-13
-50
2ND HARMONIC DISTORTION (dBc)
-74
1
-24
MAX3509-15
-42
-110
0
10
20
30
40
50
60
70
SPAN 5MHz
CENTER 22MHz
500kHz/div
FREQUENCY (MHz)
____________________________________________________________________________________
5
MAX3509
Typical Operating Characteristics (continued)
(MAX3509 EV kit, VCC1 = VCC2 = +9V, VIN = +34dBmV, TXEN = SHDN = high, D7 = 1, fINPUT = 10MHz, ZLOAD = 75Ω through a 1:1
transformer, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(MAX3509 EV kit, VCC1 = VCC2 = +9V, VIN = +34dBmV, TXEN = SHDN = high, D7 = 1, fINPUT = 10MHz, ZLOAD = 75Ω through a 1:1
transformer, TA = +25°C, unless otherwise noted.)
-30
-40
VOUT = 66dBmV
160 ks/s
α = 0.25
-30
-50
-50
-60
-60
-70
-70
-80
-80
-90
-90
-100
-100
-110
-110
-120
-120
SPAN 1MHz
CENTER 22MHz
VOUT = 66dBmV
1280 ks/s
α = 0.25
-40
MAX3509-17
OUTPUT SPECTRUM
QPSK OUTPUT SPECTRUM
-20
MAX3509-16
MAX3509
Upstream CATV Amplifier
STOP 70MHz
START 15MHz
-130
5.5MHz/div
100kHz/div
Pin Description
PIN
NAME
FUNCTION
1
TXEN
Transmit Enable. To disable the MAX3509 and provide high input/output isolation, drive TXEN low. Drive
TXEN high for normal operation.
2
SHDN
Shutdown. To enable low-power shutdown, drive SHDN low. Drive SHDN high for normal operation.
3, 8
VCC1
Programmable-Gain Amplifier (PGA) +9V Supply. Bypass to GND1 with a 0.1µF decoupling capacitor as
close to the part as possible.
4, 7
GND1
PGA Ground. Connect to ground with a low inductance path.
5
IN+
Noninverting 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.
Inverted PGA Input. When not used, AC-coupled to ground. See IN+.
6
IN-
9–13
GND
Ground
14,17
VCC2
Power Amplifier Bias +9V Supply. Bypass to GND2 (exposed paddle) with a 0.1µF decoupling capacitor as
close to the part as possible.
15
OUT-
Inverted Output. AC-couple to output transformer. Used in conjunction with OUT+.
Noninverted Output. See OUT-.
16
OUT+
18
CS
19
SDA
Serial-Interface Data. TTL-compatible input. See Serial Interface.
20
SCLK
Serial-Interface Clock. TTL-compatible input. See Serial Interface.
Exposed
Paddle
GND2
Power Amplifier Bias Ground. Connect to ground with a low inductance path. Ensure a low thermal resistive
path to PC board. See Layout Issues.
6
Serial-Interface Enable. TTL-compatible input. See Serial Interface.
_______________________________________________________________________________________
Upstream CATV Amplifier
MAX3509
SHDN
TXEN
VCC1
PGA BIAS
PA BIAS
VCC2
IN+
OUT+
IN-
OUT-
D/A CONVERTER
MAX3509
SERIAL DATA INTERFACE
CS
SDA SCLK
Figure 1. MAX3509 Functional Diagram
Detailed Description
The following sections describe the blocks shown in the
functional diagram (Figure 1).
Programmable-Gain Amplifier
The PGA consists of the variable-gain amplifier (VGA)
and the digital-to-analog converter (DAC), which provide better than 55dB 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 1 and 2).
Specified performance is achieved when the input is
driven differentially. The device may be driven single
ended; 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.
Power Amplifier
The power amplifier has two current-feedback amplifiers in an instrumentation amplifier configuration. This
architecture provides superior even-order distortion
performance but requires an external transformer to
convert to a single-ended output. In transmit-disable
mode, bias to the power amplifier is reduced to a minimal level, which provides high input to output isolation
and low output noise.
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 1 and 2 show the register format. Serial-interface timing is shown in Figure 2.
PGA Bias Cell
The bias cell in the MAX3509 is controlled by the logic
levels present at TXEN and SHDN, as well as the program state of D7, the MSB of the 8-bit program word.
Transmit-disable mode is actuated when the TXEN pin
is driven to a logic low or when D7 = 0. In this mode,
current to the PGA and power amps is reduced significantly while maintaining normal current flow to the serial data interface and DAC. This preserves the program
stored in the serial data interface.
A logic low at the SHDN pin overrides the state of the
TXEN pin or D7. In shutdown mode, the current to the
PGA, power amp, serial data interface, and DAC is cut
off, allowing only leakage currents to flow. The stored
gain control program is lost in this mode.
_______________________________________________________________________________________
7
MAX3509
Upstream CATV Amplifier
Power Amp Bias Cell
G
A
The power amp bias cell is used to enable and disable
bias to the output power amplifier. This is controlled by
TXEN and SHDN.
C
B
D
F
E
Functional Modes
The MAX3509 has three functional modes controlled
through the serial interface or external pins (Table 2):
transmit mode, transmit-disable mode, and shutdown.
Transmit Mode
Transmit mode is the normal active mode of the
MAX3509. Drive TXEN and SHDN high, and set D7 = 1
to activate transmit mode.
D7
D6
D4
D5
D2
D1
D0
E. tSCKH
F. tSENH
G. tDATAH/tDATAL
A. tSENS
B. tSDAS
C. tSDAH
D. tSCKL
Transmit-Disable Mode
When in transmit-disable mode, all analog circuitry is
shut down. This mode is activated by driving TXEN low
or setting D7 = 1 while keeping SHDN high. This mode
is typically used between bursts in TDMA systems.
Transients are controlled by the transformer balance.
D3
Figure 2. Serial-Interface Timing Diagram
Table 1. Serial-Interface Control Word
Shutdown Mode
In normal operation, the shutdown pin (SHDN) is held
high. When SHDN is driven low, all circuits within the IC
are disabled. Only leakage currents flow in this mode.
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.
BIT
MNEMONIC
DESCRIPTION
MSB 7
D7
Transmit Disable
6
D6
Not used
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
Table 2. Truth Table
SHDN
TXEN
D7
D6
D5
D4
D3
D2
D1
D0
GAIN CONTROL
WORD
0
X
X
X
X
X
X
X
X
X
X
Shutdown Mode
1
0
X
X
X
X
X
X
X
X
X
Transmit-Disable Mode
1
X
0
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 = -25dB*
1
1
1
X
0
0
0
0
0
1
1
Gain = -24dB*
1
1
1
X
—
—
—
—
—
—
—
1
1
1
X
0
1
1
0
0
1
25
1
1
1
X
—
—
—
—
—
—
—
—
1
1
1
X
1
1
1
1
1
0
62
Gain = 35dB*
1
1
1
X
1
1
1
1
1
1
63
Gain = 36dB*
STATE
—
Gain = 0dB*
*Typical gain at +25°C and VCC = +9V.
8
_______________________________________________________________________________________
Upstream CATV Amplifier
Transformer
To maintain rated performance into a 75Ω load, a 1:1
impedance ratio output transformer with adequate
bandwidth is required. A step-up transformer with a
1:1.5 impedance ratio will increase gain and output
voltage swing nominally by 1.7dB, but output noise performance will increase by the same amount.
Input Circuit
To achieve rated performance, the input of the
MAX3509 must be driven differentially with 34dBmV or
lower input level. The MAX3509 can be driven from a
single-ended source. A slight degradation in evenorder distortion at a 10W output level will result. The differential input impedance is approximately 1.2kΩ.
Most applications require a differential lowpass filter
preceding the MAX3509. The filter design dictates a
terminating resistance of a specified value. Place this
resistance across the AC-coupled inputs (see Typical
Operating Circuit).
The MAX3509 has sufficient gain to produce an output
level of 66dBmV 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 improve. If an input level greater than
34dBmV is used, distortion performance degrades.
If a single-ended source drives the MAX3509, 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 50Ω source
impedance, a value of 0.1µF will suffice.
A typical model for the MAX3509 input impedance is
shown in Figure 3.
Layout Issues
A well-designed PC board is an essential part of an RF
circuit. For best performance, pay attention to powersupply layout issues, as well as the output circuit layout.
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.
Output Circuit Layout
The differential implementation of the MAX3509’s output has the benefit of reducing even-order distortion,
the most significant of which is second-harmonic distortion. The degree of distortion cancellation depends on
the amplitude and phase balance of the overall circuit.
It is important that the traces that lead from the output
pins be the same length.
Power-Supply Layout
To achieve 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 powersupply traces branch out from this node, each going to
a separate power-supply node in the MAX3509 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
power-supply 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 GND, GND1,
and GND2 should be made with multiple vias if possible.
IN+
2.5k
1.9pF
IN-
Figure 3. Typical Equivalent Input Circuit
Exposed Paddle Thermal Considerations
The exposed paddle (EP) of the MAX3509’s 20-pin
TSSOP-EP package provides a low thermal resistance
path to the die. It is important that the PC board on
which the MAX3509 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.
Chip Information
TRANSISTOR COUNT: 1085
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9
MAX3509
Applications Information
Upstream CATV Amplifier
TSSOP.EPS
MAX3509
Package Information
10
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Upstream CATV Amplifier
MAX3509
NOTES
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11
MAX3509
Upstream CATV Amplifier
NOTES
12 _________________________________________________________________________________________________