AD8320-EB Analog Devices Inc, AD8320-EB Datasheet - Page 12

• Manufacturer Part Number: AD8320-EB
• Description: BOARD EVAL FOR AD8320
• Manufacturer: Analog Devices Inc

Specifications of AD8320-EB

• Rohs Status: RoHS non-compliant
• Channels Per Ic: 1 - Single
• Amplifier Type: Variable Gain
• Output Type: Single-Ended
• -3db Bandwidth: 150MHz
• Operating Temperature: -40°C ~ 85°C
• Current - Supply (main Ic): 97mA
• Voltage - Supply, Single/dual (±): 5 V ~ 12 V
• Board Type: Fully Populated
• Utilized Ic / Part: AD8320
• Lead Free Status / Rohs Status: Not Compliant

AD8320
75 , a supply voltage of at least +10 V is required. To achieve
a signal level of +12 dBm (about 3.1 V p-p) into 75 , a mini-
mum supply level of +5 V is required. However, for the lowest
possible distortion, the power supply voltage should be raised as
high as possible. In varying the power supply from +5 V to
+12 V, the quiescent current increases from 80 mA to 97 mA.
Careful attention must be paid to decoupling the power supply
pins. A 10 F capacitor, located fairly close to the device, is
required to provide good decoupling for lower frequency signals.
In addition, five 0.1 F decoupling capacitors should be located
close to each of the five power supply pins (7, 8, 9, 17 and 20).
A 0.1 F capacitor must also be connected to the pin labeled
BYP (Pin 14), to provide decoupling to an internal node of the
device. All six ground pins should be connected to a low imped-
ance ground plane.
Alternative Power-Down Mode
As previously mentioned, the AD8320 can be put into a low
power sleep mode by pulling the PD pin low. If lower power
consumption is required during power-down mode, an alternative
scheme can be used as shown in Figure 46.
POWER-
QUIESCENT
DATEN
SDATA
DOWN
Figure 46. Alternative Power-Down Mode with Timing
CURRENT
CLK
POWER-
OUTPUT
V2
V1
PD
DOWN
DATEN
SDATA
CLK
0.1 F
V1
V2
PD
14
97mA
0V
0V
3–5V
0V
0V
PD
AD8320
0mA
10–12V
3–5V
G
GND
VCC+12V
*
VCC
75
* ADDITIONAL PINS AND DECOUPLING CAPACITORS
S
OMITTED FOR CLARITY
D
VOCM
IRLML5103
VOUT
32mA
0.01 F
0.1 F
97mA
(
J2
SEE TEXT)
AS103
V2
J1
V1
0.1 F
J3
VDD
0.1 F
0.1 F
VOUT
+5V
75
–12–
A HEXFET power MOSFET (International Rectifier part num-
ber IRLML5103) is used to turn on and off the current to the
supply pins of the AD8320. Under normal operating conditions,
the gate (labeled POWER-DOWN) should be grounded. Pull-
ing the gate to within 2 V of the supply will open the switch and
reduce the current to the amplifier to zero.
In cable modem and cable telephony applications the modem
must always present an output impedance of 75
This forces the line driver to always present a 75
to the diplexer. In this application, a single pole double throw
RF switch (AS103, Alpha Semiconductor) is used to switch in
an external 75
This resistor then mimics the dynamic output impedance of the
AD8320. TTL or CMOS logic can be used to drive the two
voltages driving the RF switch (V1 and V2).
Before the AD8320 is turned back on again, the gain needs to
be set to a known level. This can be done by holding the PD pin
of the AD8320 low after POWER-DOWN has gone high. While
PD is held low, the 8-bit serial data stream can be clocked into
the AD8320. During this time the quiescent current will in-
crease to 32 mA. However, this time period can be as small as
about 1 s. In this mode the output settles about 45 ns after the
rising edge of PD.
Alternatively, if DATEN is held low as the AD8320 is powered
on, the device will power up in minimum gain. In this mode, the
output settles after about 200 s. Note that for both cases, the
capacitor on VOCM has been reduced from 0.1 F to 0.01 F
to facilitate a faster turn-on time. All other capacitors in the
circuit should be connected as shown in Figure 45.
impedance when the AD8320 is turned off.
to the line.
impedance
REV. 0