LT5534 データシートの表示（PDF） - Linear Technology
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LT5534 Datasheet PDF : 10 Pages
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LT5534
APPLICATIONS INFORMATION
downward to tailor for a particular application need. By
simply inserting an attenuator in front of the RF input, the
power range is shifted higher by the amount of the attenu-
ation. Moreover, due to the high RF input impedance of
the LT5534, the detecting range can be moved downward
for better detection sensitivity by using a narrow band
L-C matching network. By this means, the sensitivity of
the detector can be extended to as low as –75dBm. By
changing the value of resistor R1, the sensitivity of the
detector can be fine-tuned within the range from –75dBm
to –62dBm. Though the range is adjustable, the overall
linear dynamic range remains the same.
Output Interface
The output interface of the LT5534 is shown in Figure 4.
The output currents from the RF detectors are summed
and converted into an output voltage, VOUT. The maximum
charging current available to the output load is about
200µA. The internal compensation capacitor CC is used
to guarantee stable operation for a large capacitive output
load. The slew rate is 133V/µs, and the small-signal output
bandwidth is approximately 30MHz when the output is
resistively terminated or open. The fastest output transient
response is achieved when a large signal is applied to the
RF input port. See the Output Transient Response plot in
the Typical Performance Characteristics section.
When the output is terminated with a load capacitance
CL, the slew rate is then limited to 200µA/(CL + 1.5pF).
For example, the slew rate is reduced to 17.4V/µs when
CL = 10pF. A capacitive load may result in output voltage
overshoot, which can be minimized with a series compen-
sation resistor R2, as shown in Figure 1. The suggested
resistor values for various capacitive loads are listed in
Table 2.
Table 2. Resistor Value for Capacitive Output
C5 (pF)
R2 (kΩ)
1.5
5
5
4
10
2.5
20
2
The optional RC network at the output (R2 and C5 on the
demo board) can also provide further output filtering, if
needed. The output bandwidth is primarily dictated by the
RC constant of this lowpass filter when its corner frequency
is less than 30MHz.
When a large signal (e.g., –2dBm) is present at the RF
input port, the output voltage swing can be as high as
2.4V. To assure proper operation of the chip, the minimum
resistive load at the output termination should be greater
than 18kΩ.
VCC
+
–
OUTPUT CURRENTS
FROM RF DETECTORS
+
CC
200µA
VOUT
5534 F04
Figure 4. Simplified Circuit Schematic
of the Output Interface
5534fc
8
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