MAX1474 Просмотр технического описания (PDF) - Maxim Integrated
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MAX1474 Datasheet PDF : 8 Pages
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Miniature Electronically Trimmable Capacitor
Typical Operating Characteristics (continued)
(VDD = +5V, VSS = 0, TA = +25°C, unless otherwise noted.)
SMITH CHART:
15 DAT PULSES
SMITH CHART:
31 DAT PULSES
f1
f1
f1 = 962MHz
f1 = 848MHz
Pin Description
PIN
NAME
FUNCTION
1
CP
Capacitor Pin Connected to High-Impedance Node. See Detailed Description.
2
VDD
Positive Supply Pin. Connect a 0.01µF capacitor to VSS.
3
EN
Programming Enable Pin. Has an internal 50kΩ pulldown resistor to VSS.
4
DAT
Programming Data Pin. Has an internal 50kΩ pulldown resistor to VSS.
5
VSS
Negative Supply Pin
6
CM
Capacitor Pin Connected to Low-Impedance Node. See Detailed Description.
Detailed Description
The MAX1474 consists of a binary-weighted array of
capacitors that can be switched in and out of parallel to
provide 32 monotonic steps. The switches implement-
ed allow the DC bias of either terminal of the capacitor
to be anywhere from ground to the supply voltage.
There is no inherent polarity. The signal swing range is
limited to 300mV above VDD and 300mV below VSS.
Therefore, if a large-signal swing range is desired, care
must be taken to bias the terminal(s) requiring high
swing capability near midsupply.
If the capacitance is measured differentially from one
terminal to the other, the greatest min/max ratio of the
binary array can be realized, allowing tuning from
0.42pF to 10.9pF in 0.34pF steps. If one terminal is
grounded, and the capacitance is measured to ground,
the parasitics inherent in the package will become
lumped with the switched array, allowing tuning from
6.4pF to 13.3pF in 0.22pF steps. When using the
MAX1474, it is recommended for optimal performance
to connect the CM terminal to the lowest impedance
node (i.e., ground or supply if possible) and CP to the
higher impedance node (i.e., the resonant node in a
ground-referenced LC tank circuit).
Digital Interface
The digital interface sets the desired capacitance
value. There are only two pins, EN and DAT, required
for this operation. EN is an active-high control signal.
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