AD8362
To operate in controller mode, the link between VSET and
VOUT is broken. A setpoint voltage is applied to the VSET
input, while VOUT is connected to the gain control terminal
of the VGA, and the AD8362 RF input is connected to the out-
put of the VGA (generally using a directional coupler or power
splitter and some additional attenuation). Based on the defined
relationship between VOUT and the RF input signal when the
device is in measurement mode, the AD8362 adjusts the voltage
on VOUT (VOUT is now an error amplifier output) until the
level at the RF input corresponds to the applied VSET. For
example, in a closed loop system, if VSET is set to 3 V, VOUT
increases or decreases until the input signal is equal to 0 dBm.
This relationship follows directly from the measurement mode
transfer function (see Figure 10, Figure 11, and Figure 12).
Therefore, when the AD8362 operates in controller mode, there
is no defined relationship between VSET and VOUT. VOUT
settles to a value that results in balance between the input signal
levels appearing at INHI/INLO and VSET.
OPERATION IN CONTROLLER MODE
The AD8362 provides a controller mode feature at the VOUT
pin. Using VSET for the setpoint voltage, it is possible for the
AD8362 to control subsystems such as power amplifiers (PAs),
VGAs, or variable voltage attenuators (VVAs), which have
output power that decreases monotonically with respect to
their (increasing) gain control signal.
CONTROLLED SYSTEM
(OUTPUT POWER
DECREASES AS
VAPC INCREASES)
P
P
OUTPUT
INPUT
OUT
IN
VAPC
OUTPUT CONTROL VOLTAGE
0.1V TO 4.9V
V
S
AD8362
ATTN
1
2
3
4
5
6
7
8
COMM
CHPF
DECL
INHI
16
15
14
13
12
11
10
9
ACOM
VREF
VTGT
VPOS
VOUT
VSET
ACOM
CLPF
C1
C8
1:4 Z-RATIO
0.1µF
1000pF
C4
1nF
C6
100pF
C2
1nF
C10
1000pF
INLO
C7
1nF
SETPOINT
VOLTAGE
INPUT
C5
For this output power control loop to be stable, a ground-
referenced capacitor must be connected to the CLPF pin.
This capacitor integrates the internal error current that is
present when the loop is not balanced.
DECL
PWDN
COMM
100pF
T1
ETC1.6-4-2-3
0V TO 3.5V
C3
(SEE TEXT)
Figure 64. Basic Connections for Controller Mode Operation
Increasing VSET, which corresponds to demanding a higher
signal from the VGA, tends to decrease VOUT. The VGA or VVA
therefore must have a negative sense. In other words, increasing
the gain control voltage decreases gain. If this is not the case, an
op amp, configured as an inverter with suitable level shifting, can
be used to correct the sense of the VOUT signal.
Rev. D | Page 26 of 32
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