MAXIM MAX3505EGP

19-2351; Rev 0; 4/02
KIT
ATION
EVALU
E
L
B
A
AVAIL
Upstream CATV Amplifier
Features
♦ Single 5V Supply Operation
♦ Accurate Gain Control, ±1dB over 56dB Range
♦ Gain Programmable in 0.5dB Steps
♦ -55dBc Harmonic Distortion at 65MHz
♦ Low Burst On/Off Transient
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX3505EGP
-40°C to +85°C
20 QFN-EP* (5mm × 5mm)
*EP = exposed pad
The MAX3505 is available in a 20-pin QFN package.
The device operates in the extended industrial temperature range (-40°C to +85°C).
Applications
DOCSIS/EuroDOCSIS and DVB Cable
Modems
Pin Configuration
OpenCable Set-Top Box
Typical Operating Circuit
10
SHDN
9
VCC
TXEN
0.001µF
5V
N.C.
N.C.
CEXT
18
17
16
2
14
OUT+
GND
3
13
N.C.
IN-
4
12
OUT-
GND
5
11
N.C.
MAX3505
8
9
10
SHDN
12
CS
OUT-
TXEN
MAX3505
IN-
0.1µF
0.001µF
0.1µF
IN+
7
4
-
VCC
IN+
ANTI-ALIAS
FILTER
+5V
OUTPUT
15
SCLK
INPUT
OUT+
1:1
14
1
6
2
+
0.1µF
5V
15
VCC
SDA
CONTROL
LOGIC
N.C.
DOCSIS/EuroDOCSIS/OpenCable are trademarks of CableLabs.
19
TOP VIEW
SPI is a trademark of Motorola, Inc.
N.C.
CATV Status Monitor
20
Telephony Over Cable
1
4
0.1µF
VCC
CEXT
GND
GND
16
5
QFN**
6
SDA
SCLK
CS
7
8
CONTROL
LOGIC
**NOTE: THE EXPOSED PAD MUST BE SOLDERED TO GROUND.
________________________________________________________________ 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
MAX3505
General Description
The MAX3505 programmable power amplifier is
designed for use in CATV upstream applications. The
MAX3505 drives 64dBmV (QPSK) into a 75Ω 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 SPI™ 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 5µA (typ).
MAX3505
Upstream CATV Amplifier
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 = +85°C)
20-Pin QFN (derate 27mW/°C above +85°C) .............1800mW
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
(MAX3505EV kit; VCC = 4.75V to 5.25V, VGND = 0V, TXEN = SHDN = high, TA = -40°C to +85°C. Typical parameters are at VCC =
5.0V, TA = +25°C, unless otherwise specified.) (Note1)
PARAMETER
SYMBOL
Supply Voltage
VCC
Supply-Current Transmit Mode
ICC
Supply-Current Transmit Disable
Mode
Supply-Current Low-Power
Standby
CONDITIONS
MIN
TYP
4.75
D7 = 1, gain code = 123 (Av = 31dB)
285
D7 = 0, gain code = 92 (Av = 0dB)
55
ICC
TXEN = low
4.8
ICC
SHDN = low
5
MAX
UNITS
5.25
V
335
7
mA
mA
µA
LOGIC INPUTS
Input High Voltage
VINH
Input Low Voltage
VINL
2.0
Input High Current
IBIASH
VINH = 3.3V
Input Low Current
IBIASL
VINL = 0V
V
0.8
V
100
µA
-100
µA
AC ELECTRICAL CHARACTERISTICS
(MAX3505 EV kit; VCC = 4.75V to 5.25V, VGND = 0V, PIN = 34dBmV, TXEN = SHDN = high, TA = -40°C to +85°C. Typical parameters
are at TA =+25°C, unless otherwise specified.) (Note 1)
PARAMETER
Voltage Gain, fIN = 5MHz
2
SYMBOL
AV
CONDITIONS
MIN
TYP
MAX
D7 = 1, gain code = 123, TA = 0°C to +85°C
29.5
31
32.5
D7 = 1, gain code = 119, TA = 0°C to +85°C
27.5
29
30.5
D7 = 1, gain code = 99, TA = 0°C to +85°C
17.5
19
20.5
D7 = 1, gain code = 82, TA = 0°C to +85°C
9
10.5
12
D7 = 0, gain code = 112, TA = 0°C to +85°C
8
9.5
11
D7 = 0, gain code = 92, TA = 0°C to +85°C
-2
-0.5
+1
D7 = 0, gain code = 72, TA = 0°C to +85°C
-12
-10.5
-9
D7 = 0, gain code = 43, TA = 0°C to +85°C
-26.5
-25.0
-23.5
_______________________________________________________________________________________
UNITS
dB
Upstream CATV Amplifier
(MAX3505 EV kit; VCC = 4.75V to 5.25V, VGND = 0V, PIN = 34dBmV, TXEN = SHDN = high, TA = -40°C to +85°C. Typical parameters
are at VCC = 5.0V, TA = +25°C, unless otherwise specified.) (Note1)
PARAMETER
Voltage Gain, fIN = 65MHz
SYMBOL
AV
CONDITIONS
D7 = 1, gain code = 125, TA = -40°C to
+85°C (Note 2)
MIN
TYP
MAX
29.0
UNITS
dB
VOUT = 64dBmV, fIN = 5MHz to 42MHz
(Note 2)
-0.5
-0.85
VOUT = 64dBmV, fIN = 5MHz to 65MHz
(Note 2)
-0.85
-1.35
Gain Rolloff
dB
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
0.7
1.0
1.3
fIN = 5MHz to 65MHz, D7 = 0, gain code =
112; to D7 = 1, gain code = 82
0.65
1.0
1.35
Transmit-Disable Mode Noise
TXEN = low, BW = 160kHz, fIN = 5MHz to
65MHz (Note 2)
Isolation in Transmit-Disable
Mode
TXEN = low, fIN = 5MHz to 65MHz (Note 2)
Transmit Mode Noise
BW = 160kHz, fIN = 5MHz to 65MHz,
AV = -26dB to +30dB (Note 2)
Transmit Enable Transient
Duration
Transmit Disable Transient
Duration
-65
60
dB
dBmV
dB
-55
dBc
TXEN input rise/fall time < 0.1µs (Note 2)
2
µs
TXEN input rise/fall time < 0.1µs (Note 2)
2
µs
D7 = 1, gain code = 119 (AV = 29dB)
Transmit Disable/ Transmit
Enable Transient Step Size
0.5
30
D7 = 1, gain code = 83 (AV = 11dB)
80
20
mVP-P
D7 = 0, gain code = 92 (AV = -0.5dB)
3
fIN = 5MHz to 65MHz, differential (Note 2)
2
kΩ
Output Return Loss
fIN = 5MHz to 65MHz, in 75Ω system, D7 = 1,
gain code = 119 (AV = 27dB)
10
dB
Output Return Loss in TransmitDisable Mode
fIN = 5MHz to 65MHz, in 75Ω system,
TXEN = low
10
dB
Input Impedance
ZIN
_______________________________________________________________________________________
3
MAX3505
AC ELECTRICAL CHARACTERISTICS (continued)
MAX3505
Upstream CATV Amplifier
AC ELECTRICAL CHARACTERISTICS (continued)
(MAX3505 EV kit; VCC = 4.75V to 5.25V, VGND = 0V, PIN = 34dBmV, TXEN = SHDN = high, TA = -40°C to +85°C. Typical parameters
are at TA =+25°C, unless otherwise specified.) (Note 1)
PARAMETER
Two-Tone Third-Order Distortion
SYMBOL
IM3
2nd Harmonic Distortion
HD2
3rd Harmonic Distortion
HD3
CONDITIONS
MIN
TYP
MAX
Input tones at 42MHz and 42.2MHz, both
31dBmV, VOUT = 60dBmV/tone (Note 2)
-53
-47
Input tones at 65MHz and 65.2MHz, both
31dBmV, VOUT = 60dBmV/tone
-47
fIN = 33MHz, VOUT = 64dBmV
-55
-50
fIN = 65MHz, VOUT = 64dBmV (Note 2)
-55
-50
fIN = 22MHz, VOUT = 64dBmV
-55
-50
fIN = 65MHz, VOUT = 64dBmV
-55
-48.5
UNITS
dBc
dBc
dBc
TIMING CHARACTERISTICS
(VCC = 4.75V to 5.25V, VGND = 0V, TXEN = SHDN = high, TA = +25°C, D7 = 1, unless otherwise specified.)
PARAMETER
SEN to SCLK Rise Set Time
SYMBOL
tSENS
CONDITIONS
MIN
20
TYP
MAX
UNITS
ns
SEN to SCLK Rise Hold Time
tSENH
10
ns
SDA to SCLK Setup Time
tSDAS
10
ns
SDA to SCLK Hold Time
tSDAH
20
ns
SDA Pulse-Width High
TDATAH
50
ns
SDA Pulse-Width Low
TDATAL
50
ns
SCLK Pulse-Width High
tSCLKH
50
ns
SCLK Pulse-Width Low
tSCLKL
50
ns
Note 1: All parameters are guaranteed by design and characterization to ±3 sigma for TA < +25°C, unless otherwise specified.
Note 2: Guaranteed by design and characterization to ±6 sigma.
4
_______________________________________________________________________________________
Upstream CATV Amplifier
150
TRANSMIT-ENABLE MODE,
LOW NOISE, GAIN CODE = 92
GAIN CODE = 123
31.5
+25°C
300
VOLTAGE GAIN (dB)
200
100
350
SUPPLY CURRENT (mA)
TRANSMIT-ENABLE MODE,
HIGH POWER, GAIN CODE = 123
250
32.0
MAX3505 toc02
300
SUPPLY CURRENT (mA)
400
MAX3505 toc01
350
VOLTAGE GAIN vs. SUPPLY VOLTAGE
HIGH-POWER MODE
SUPPLY CURRENT vs. GAIN CODE
MAX3505 toc03
SUPPLY CURRENT vs. TEMPERATURE
250
200
150
HIGH-POWER MODE
31.0
30.5
+85°C
-40°C
30.0
100
LOW-NOISE MODE
50
29.5
50
TRANSMIT-DISABLE MODE
-25
0
25
50
75
0
20
40
60
80
100
120
5.0
5.1
5.2
VOLTAGE GAIN vs. TEMPERATURE
HIGH-POWER MODE
VOLTAGE GAIN vs. TEMPERATURE
LOW-NOISE MODE
GAIN CODE = 123
31.5
30.5
VCC = 5.25V
30.0
4.8
4.9
5.0
5.1
5.2
-40
5.3
-15
10
35
60
SUPPLY VOLTAGE (V)
TEMPERATURE (°C)
VOLTAGE GAIN vs. FREQUENCY
HIGH-POWER MODE
VOLTAGE GAIN vs. FREQUENCY
LOW-NOISE MODE
A
25
B
15
10
C
5
0
A
10
VOLTAGE GAIN (dB)
20
-20
GAIN CODE
A = 112, B = 92,
C = 72, D = 43
-40
-15
10
100
FREQUENCY (MHz)
1000
1
10
100
FREQUENCY (MHz)
10
35
60
85
VOLTAGE GAIN vs. GAIN CODE
D
-30
-15
TEMPERATURE (°C)
C
-10
-40
85
B
0
D
GAIN CODE
A = 123, B = 99,
C = 82, D = 62
-11.0
VOLTAGE GAIN (dB)
30
20
MAX3505 toc07
35
VCC = 4.75V
-10.5
MAX3505 toc08
4.7
-10.0
-12.0
29.0
-26.0
VCC = 5.25V
-11.5
29.5
-25.5
VCC = 5V
1000
35
30
25
20
15
10
5
0
-5
-10
-15
-20
-25
-30
-35
MAX3505 toc09
+85°C
31.0
VCC = 5V
GAIN CODE = 72
-9.5
VOLTAGE GAIN (dB)
-24.5
VCC = 4.75V
5.3
-9.0
MAX3505 toc05
MAX3505 toc04
+25°C
-25.0
32.0
VOLTAGE GAIN (dB)
-24.0
1
4.9
VOLTAGE GAIN vs. SUPPLY VOLTAGE
LOW-POWER MODE
-40°C
-5
4.8
SUPPLY VOLTAGE (V)
-23.5
-10
4.7
140
GAIN CODE
GAIN CODE = 43
VOLTAGE GAIN (dB)
100
TEMPERATURE (°C)
-23.0
VOLTAGE GAIN (dB)
29.0
0
-50
MAX3505 toc06
0
HIGH-POWER MODE
LOW-NOISE MODE
30
40
50 60 70
80 90 100 110 120
GAIN CODE
_______________________________________________________________________________________
5
MAX3505
Typical Operating Characteristics
(Typical applications circuit; VCC = 5V, VIN = 34dBmV, TXEN = SHDN = high, fIN = 20MHz, ZLOAD = 75Ω, TA = +25°C, unless otherwise noted.)
Typical Operating Characteristics (continued)
(Typical applications circuit; VCC = 5V, VIN = 34dBmV, TXEN = SHDN = high, fIN = 20MHz, ZLOAD = 75Ω, TA = +25°C, unless otherwise noted.)
GAIN STEP vs. GAIN CODE
LOW-NOISE MODE
0.8
GAIN STEP (dB)
0.7
0.9
0.6
0.5
0.4
0.6
0.5
0.4
0.3
0.3
0.2
0.2
0
0
70
80
90
100
110
120
40
50
60
70
80
90 100 110 120
30
90
50dBmV, HP
-65
20dBmV, LN
-70
6dBmV, LN
-75
-80
OUTPUT RETURN LOSS vs. FREQUENCY
(75Ω SYSTEM)
OUTPUT IMPEDANCE
(75Ω SYSTEM)
40
50
0
HIGH-POWER MODE
60
70
0
10
20
30
MAX3505 toc16
30
LOW-NOISE MODE/
TRANSMITDISABLE MODE
HIGH-POWER MODE
1
0.1
70
0
LOW-NOISE MODE/
TRANSMIT-DISABLE
MODE
20
40
60
80
-10
-20
VOUT = 61dBmV
∝ = 0.25
1280ksps
-30
-40
-50
-70
-80
-25
-90
-30
-100
10
100
500kHz/div
FREQUENCY (MHz)
6
120
140
OUTPUT SPECTRUM
0
-60
HIGH-POWER MODE
100
GAIN CODE
(dB)
-10
60
MAX3505 toc17
INPUT FREQUENCY (MHz)
50
40
INPUT FREQUENCY (MHz)
20
10
LOW-NOISE MODE
-90
10
130
MAX3505 toc15
64dBmV, HP
-60
100
-85
-95
1
110
MAX3505 toc18
6dBmV, LN
-90
-55
TRANSIENT LEVEL (mVP-P)
-85
-50
MAX3505 toc14
MAX3505 toc13
-80
-20
70
POWER-UP/DOWN TRANSIENTS
vs. GAIN CODE
20dBmV, LN
-15
50
3RD HARMONIC DISTORTION
vs. INPUT FREQUENCY
50dBmV, HP
-5
LOW-NOISE MODE
2ND HARMONIC DISTORTION
vs. INPUT FREQUENCY
-65
0
-45
GAIN CODE
64dBmV, HP
-75
-40
GAIN CODE
-55
-70
-35
GAIN CODE
-50
-60
HIGH-POWER MODE
-30
-55
30
3RD HARMONIC DISTORTION (dBc)
60
-25
-50
0.1
0.1
2ND HARMONIC DISTORTION (dBc)
0.7
-20
MAX3505 toc12
0.8
TRANSMIT NOISE vs. GAIN CODE
MAX3505 toc11
0.9
GAIN STEP (dB)
1.0
MAX3505 toc10
1.0
OUTPUT NOISE (dBmV IN 160kHz)
GAIN STEP vs. GAIN CODE
HIGH-POWER MODE
OUTPUT RETURN LOSS (dB)
MAX3505
Upstream CATV Amplifier
_______________________________________________________________________________________
Upstream CATV Amplifier
OUTPUT SPECTRUM
-20
-30
-30
-40
-40
-50
-50
-60
-60
-70
-70
-80
-80
-90
-90
-100
-100
100kHz/div
VOUT = 61dBmV
∝ = 0.25
1280ksps
-10
(dB)
(dB)
-20
VOUT = 61dBmV
∝ = 0.25
160ksps
MAX3505 toc20
-10
OUTPUT SPECTRUM
0
MAX3505 toc19
0
6MHz/div
Pin Description
PIN
NAME
FUNCTION
1
VCC
Programmable-Gain Amplifier (PGA) +5V Supply. Bypass to GND with a 0.1µF decoupling
capacitor as close to the part as possible.
2
IN+
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.
3
GND
PGA RF Ground. As with all ground connections, maintain the shortest possible (low-inductance)
length to the ground plane.
4
IN-
5
GND
Ground
6
SDA
Serial-Interface Data. TTL-compatible input. See the Serial Interface section.
7
SCLK
Serial-Interface Clock. TTL-compatible input. See the Serial Interface section.
8
CS
Serial-Interface Enable. TTL-compatible input. See the Serial Interface section.
9
TXEN
Transmit Enable. Drive TXEN high to place the device in transmit-enable mode.
10
SHDN
Shutdown. When SHDN is set low, all functions (including the serial interface) are disabled.
11,13,17–20
N.C.
No Connection
12
OUT-
Negative Output. Along with OUT+, this port forms a 75Ω impedance output. This port is matched
to a 75Ω load using a 1:1 transformer.
14
OUT+
Positive Output. See OUT-.
15
VCC
16
CEXT
RF Output Bypass. Bypass to GND with a 0.1µF capacitor.
Exposed
Pad
GND
Ground
Negative PGA Input. When not used, this port must be AC-coupled to ground. See IN+.
Output Amplifier Bias, +5V Supply. Bypass to GND with a 0.1µF decoupling capacitor as close to
the part as possible.
_______________________________________________________________________________________
7
MAX3505
Typical Operating Characteristics (continued)
(Typical applications circuit; VCC = 5V, VIN = 34dBmV, TXEN = SHDN = high, fIN = 20MHz, ZLOAD = 75Ω, TA = +25°C, unless otherwise noted.)
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
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 0.001µF
capacitor is suggested.
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
8
GND
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 75Ω 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.
_______________________________________________________________________________________
Upstream CATV Amplifier
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).
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 5µA (typ) in shutdown mode.
G
A
High-Power and Low-Noise Modes
D7
D6
C
B
D5
A. tSENS
B. tSDAS
C. tSDAH
D. tSCKL
D4
D3
D
D2
F
E
D1
MAX3505
Applications Information
D0
E. tSCKH
F. tSENH
G. tDATAH/tDATAL
Figure1. Serial-Interface Timing Diagram
Table 1. Serial-Interface Control Word
BIT
MNEMONIC
DESCRIPTION
MSB 7
D7
High-power/low-noise mode select
6
D6
Gain code, bit 6
5
D5
Gain code, bit 5
Transformer
4
D4
Gain code, bit 4
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 50Ω source on the primary
and a matching resistance on the secondary winding.
Operating in a 75Ω 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 0°C),
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.
3
D3
Gain code, bit 3
2
D2
Gain code, bit 2
1
D1
Gain code, bit 1
LSB 0
D0
Gain code, bit 0
Input Circuit
To achieve rated performance, drive the inputs of the
MAX3505 differentially with an appropriate input level.
The differential input impedance is approximately 2kΩ.
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.
_______________________________________________________________________________________
9
MAX3505
Upstream CATV Amplifier
Table 2. Chip-State Control Bits
GAIN CODE
(DECIMAL)
SHDN
TXEN
D7
D6
D5
D4
D3
D2
D1
D0
0
X
X
X
X
X
X
X
X
X
Shutdown Mode
1
0
X
X
X
X
X
X
X
X
Transmit-Disable Mode
1
1
1
X
X
X
X
X
X
X
Transmit-Enable Mode, High Power
1
1
0
X
X
X
X
X
X
X
Transmit-Enable Mode, Low Noise
1
1
0
0
1
0
1
0
1
1
43
AV = -25.0dB*
1
1
0
1
0
1
1
1
0
0
92
AV = -0.5dB*
1
1
0
1
1
1
0
0
0
0
112
AV = 9.5dB*
1
1
1
1
0
1
0
0
1
0
82
AV = 10.5dB*
1
1
1
1
1
0
0
0
1
1
99
AV = 19.0dB*
1
1
1
1
1
1
1
0
1
1
123
AV = 31.0dB*
STATES
*Typical gain at +25°C, 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 75Ω source
impedance, a value of 0.001µF suffices.
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.
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.
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.
10
______________________________________________________________________________________
Upstream CATV Amplifier
______________________________________________________________________________________
11
MAX3505
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
Upstream CATV Amplifier
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
© 2002 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.