MAX4000/MAX4001/MAX4002 Controller Mode
For operation in controller mode, both JU1 and JU2
should be removed. Use a DAC or external precision
voltage supply to apply the set-point voltage to the SET
pad. RFIN is connected to the RF source—power
amplifier (PA) output through a directional coupler—
and the OUT pad is connected to the gain-control pin
of the PA. When used in controller mode, a capacitor
must be installed in C4 for loop stability (see the Filter
Capacitor Selection section).
MAX4000/MAX4001/MAX4002 Automatic
Gain Control
To simulate an automatic gain-control (AGC) loop, a
quasi-measurement mode can be implemented where
the MAX4000/MAX4001/MAX4002 deliver an output
voltage that is proportional to the log of the input signal
(see the Quasi-Measurement Mode section). To estab-
lish the transfer function of the log amp, the RF input
power level should be swept while the voltage at the
SET pad is measured. This is the simplest method to
validate operation of the evaluation board.
Filter Capacitor Selection
When functioning as a PA controller, the MAX4000/
MAX4001/MAX4002 require some capacitance to main-
tain loop stability. Global system for mobile (GSM) appli-
cations require a control-loop bandwidth of at least
150kHz. Install a 2200pF capacitor at the location desig-
nated by C4 (located on the board’s component side) to
obtain this control-loop bandwidth. Refer to Figure 3 of
the MAX4000/MAX4001/MAX4002 data sheet for alterna-
tive capacitor values.
Quasi-Measurement Mode
In the quasi-measurement mode, the MAX4003 EV kit
works as a log detector. This mode allows for easy
measurement of RFIN versus the SET voltage and
these measurements can then be used to find the inter-
cept and slope required for the given application.
Place a shunt on pins 2-3 of JU1 and install a shunt
across JU2 to enable the quasi-measurement mode,
which connects the OUT voltage through an inverting op
amp to the SET pin. The quasi-measurement mode
yields a nominal relationship between RFIN and SET. See
Table 1 for quasi-measurement mode shunt positions.
Shutdown Control
Jumper JU3 controls the CMOS-compatible shutdown
pin (SHDN) of the MAX4003, which disables the
MAX4003. Removing the shunt from JU3 allows the
SHDN pin to be driven with an external signal source
connected to the SHDN pad. See Table 2 for shutdown
shunt positions.
Layout Considerations
A good PC board is an essential part of RF circuit
design. The MAX4003 EV kit PC board can serve as a
guide for board layout using the MAX4000–MAX4003.
Keep traces carrying RF signals as short as possible to
minimize radiation and insertion loss due to the PC
board. Each VCC node on the PC board should have
its own decoupling capacitor. This minimizes supply
coupling from one section of the PC board to another.
Using a star topology for the supply layout, in which
each VCC node in the circuit has a separate connec-
tion to the central VCC node, can further minimize cou-
pling between sections of the PC board.
Evaluates: MAX4000–MAX4003
MAX4003 Evaluation Kit
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