ADL5500 Analog Devices, Inc., ADL5500 Datasheet - Page 17

• Manufacturer Part Number: ADL5500
• Description: 100 Mhz To 6 Ghz Trupwr Detector
• Manufacturer: Analog Devices, Inc.

OUTPUT DRIVE CAPABILITY AND BUFFERING
The ADL5500 is capable of sourcing an output current of
approximately 3 mA. The output current is sourced through the
on-chip 1 kΩ series resistor; therefore, any load resistor forms a
voltage divider with this on-chip resistance. It is recommended
that the ADL5500 drive high resistive loads to preserve output
swing (preferably >100 kΩ). If an application requires driving
a low resistance load, a simple buffering circuit can be used,
as shown in Figure 40. Similar circuits can be used to increase
or decrease the nominal conversion gain (see Figure 38 and
Figure 39). In Figure 39, the AD8031 buffers a resistive divider
to give half of the slope. In Figure 38, the op amp’s gain of two
doubles the slope. Using other resistor values, the slope can be
changed to an arbitrary value. The AD8031 rail-to-rail op amp,
used in these examples, can swing from 50 mV to 4.95 V on a
single 5 V supply and operates at supply voltages down to 2.7 V.
If high output current is required (>10 mA), the AD8051, which
also has rail-to- rail capability, can be used down to a supply
voltage of 3 V. It can deliver up to 45 mA of output current.
Figure 38. Output Buffering Options, Slope of 12.8 V/V rms at 900 MHz
Figure 39. Output Buffering Options, Slope of 3.2 V/V rms at 900 MHz
Figure 40. Output Buffering Options, Slope of 6.4 V/V rms at 900 MHz
0.1μF
0.1μF
0.1μF
ADL5500
ADL5500
ADL5500
VPOS
COMM
VPOS
COMM
COMM
VPOS
100pF
100pF
VRMS
VRMS
100pF
VRMS
4kΩ
5kΩ
AD8031
AD8031
5kΩ
AD8031
5kΩ
0.01μF
0.01μF
0.01μF
3.2V/V rms
6.4V/V rms
12.8V/V rms
5V
5V
5V
Rev. A | Page 17 of 24
VRMS OUTPUT OFFSET
The ADL5500 has a ±1 dB error detection range of about 30 dB,
as shown in Figure 10 to Figure 15. The error is referred to the
best fit line defined in the linear region of the output response.
Below an input power of −20 dBm, the response is no longer
linear and begins to lose accuracy. In addition, depending on
the supply voltage, saturation of the output limits the detection
accuracy above 10 dBm. Calibration points should be chosen in
the linear region, avoiding the nonlinear ranges at the high and
low extremes.
Figure 41 shows the distribution of the output response vs.
the input power for multiple devices. The ADL5500 loses
accuracy at low input powers as the output response begins to
fan out. As the input power is reduced, the spread of the output
response increases along with the error. Although some devices
follow the ideal linear response at very low input powers, not
all devices continue the ideal linear regression to a near 0 V
y-intercept. Some devices exhibit output responses that rapidly
decrease and some flatten out. With no RF signal applied,
the ADL5500 has a typical output offset of 40 mV (with a
maximum of 150 mV).
0.01
0.1
10
1
–40
Figure 41. Output vs. Input Level Distribution of 55 Devices,
–35
–30
Frequency 900 MHz, Supply 3.0 V
–25
–20
INPUT (dBm)
–15
–10
–5
ADL5500
0
5
10