Applications Information
The MAX2205–MAX2208 have internal termination
resistors for use with directional couplers. The applica-
tion circuit is shown in Figure 1. The output of the
detector goes to an op amp in an analog GSM power-
control scheme, or to an ADC in other systems such as
TDMA or discrete-time GSM power control.
The MAX2205 has high-input impedance for use with
high-value resistive tapping from a CDMA power ampli-
fier. This coupling method is the lowest cost and lowest
loss when used with an isolator. The application circuit
is shown in Figure 2. Connect C
FILTER
from the
MAX2205 output to GND to reduce residual amplitude
ripple. For IS98A reverse channel signal with peak-to-
avg ratio of 3.9dB, a 1.5nF capacitor gives 43mV
P-P
rip-
ple at 28dBm PA output and 390µs response time. For
CDMA2000 (pilot + DCCH) with peak-to-avg ratio of
5.4dB, the ripple is about 65mV
P-P
at 26dBm PA output.
The MAX2205 input impedance is listed in Table 1.
Layout
As with any RF circuit, the layout of the MAX2205–
MAX2208 circuits affects performance. Use a short
50Ω line at the input with multiple ground vias along the
length of the line. The input capacitor and resistor
should be placed as close to the IC as possible. The
V
CC
input should be bypassed as close as possible to
the IC with multiple vias connecting the capacitor to
ground. Refer to the MAX2205–MAX2208 EV kit data
sheet for a sample layout and details.
UCSP Reliability
The UCSP is a unique package that greatly reduces
board space compared to other packages. UCSP relia-
bility is integrally linked to the user’s assembly methods,
circuit board material, and usage environment. The user
should closely review these areas when considering
using a UCSP. This form factor might not perform equally
to a packaged product through traditional mechanical
reliability tests. Performance through operating life test
and moisture resistance remains uncompromised, as it
is determined primarily by the wafer-fabrication process.
Mechanical stress performance is a greater considera-
tion for a UCSP. UCSP solder-joint contact integrity must
be considered because the package is attached through
direct solder contact to the user’s PC board. Testing
done to characterize the UCSP reliability performance
shows that it is capable of performing reliably through
environmental stresses. Results of environmental stress
tests and additional usage data and recommendations
are detailed in the UCSP application note, which can be
found on Maxim’s website, www.maxim-ic.com.
Chip Information
TRANSISTOR COUNT: 344
MAX2205–MAX2208
RF Power Detectors in UCSP
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