LTC5530
9
5530f
APPLICATIO S I FOR ATIO
WUU
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Operation
The LTC5530 RF detector integrates several functions to
provide RF power detection over frequencies ranging from
300MHz to 7GHz. These functions include an internal fre-
quency compensated buffer amplifier, an RF Schottky di-
ode peak detector and level shift amplifier to convert the RF
input signal to DC and a delay circuit to avoid voltage tran-
sients at V
OUT
when powering up. The LTC5530 has both
shutdown and gain setting capabilities.
Buffer Amplifier
The output buffer amplifier is capable of supplying typi-
cally 4mA into a load. The negative terminal V
M
is brought
out to a pin for gain selection. External resistors connected
between V
OUT
and V
M
(R
A
) and V
M
to ground (R
B
) will set
the amplifier gain.
GAIN
R
R
A
B
=+1
The amplifier is unity gain stable; however a minimum gain
of two is recommended to improve low output voltage
accuracy. The amplifier bandwidth is 2MHz for a gain of 2.
For increased gain applications, the bandwidth is reduced
according to the formula:
BANDWIDTH
MHz
GAIN
MHz
R
RR
B
AB
==
+
4
4
()
•
()
A capacitor can be placed across the feedback resistor RA
to shape the frequency response. In addition the amplifier
can be used as a comparator. V
M
can be connected to a
reference voltage. When the internal detector voltage
(which is connected to the positive input of the buffer
amplifier) exceeds the external voltage of V
M
, V
OUT
will
switch high.
RF Detector
The internal RF Schottky diode peak detector and level
shift amplifier converts the RF input signal to a low
frequency signal. The detector demonstrates excellent
efficiency and linearity over a wide range of input power.
The Schottky diode is biased at about 55µA and drives a
25pF internal peak detector capacitor.
Shutdown
The part is in shutdown mode when SHDN is low. The
supply current is reduced to < 2µA and V
OUT
is shorted to
ground via a 280Ω resistor. When SHDN is asserted high,
the part is enabled after about 8µs.
RF
IN
GND
SHDN
V
CC
V
OUT
V
M
LTC5530ES6
1
2
3
6
5
4
C4
39pF
RF
IN
R1
(OPT)
C2
100pF
C1
0.1µF
C3
(OPT)
V
CC
2.7V TO 6V
V
OUT
5530 DB
SHDN
V
CC
R2
22k
R3
10k
R4
10k
Demo Board Schematic
