MICRF009BM TR Micrel Inc, MICRF009BM TR Datasheet - Page 8

• Manufacturer Part Number: MICRF009BM TR
• Manufacturer: Micrel Inc

Specifications of MICRF009BM TR

• Operating Band Frequency: 300 to 440MHz
• Operating Temperature (min): -40C
• Operating Temperature (max): 85C
• Operating Temperature Classification: Industrial
• Modulation Type: ASK/OOK
• Product Depth (mm): 3.94mm
• Product Height (mm): 1.48mm
• Product Length (mm): 9.93mm
• Operating Supply Voltage (min): 4.75V
• Operating Supply Voltage (typ): 5V
• Operating Supply Voltage (max): 5.5V
• Lead Free Status / Rohs Status: Not Compliant

Step 3: Selecting C
Extraction of the DC value of the demodulated signal for
purposes of logic-level data slicing is accomplished using
the external threshold capacitor C
switched capacitor “resistor” RSC, shown in the block
diagram.
Slicing level time constant values vary somewhat with
decoder type, data pattern, and data rate, but typically
values range from 5ms to 50ms.This issue is covered in
more detail in “Application Note 22.” Optimization of the
value of C
Selecting Capacitor C
The first step in the process is selection of a data-slicing-
level time constant. This selection is strongly dependent on
system issues including system decode response time and
data code structure (that is, existence of data preamble,
etc.) This issue is also covered in more detail in
“Application Note 22.”
The effective resistance of RSC is listed in the electrical
characteristics table as 145kΩ at 315MHz, this value
scales linearly with frequency. Source impedance of the
CTH pin at other frequencies is given by equation (4),
where f
τ of 5x the bit-rate is recommended. The effective
resistance of RSC is listed in the electrical characteristics
table as 145kΩ at 315MHz, this value scales inversely with
frequency. Source impedance of the CTH pin at other
frequencies is given by equation (5), where f
A standard ±20% X7R ceramic capacitor is generally
sufficient. Refer to “Application Hint 42” for C
selection examples.
Step 4: Selecting C
The signal path has AGC (automatic gain control) to
increase input dynamic range. The attack time constant of
the AGC is set externally by the value of the CAGC
capacitor connected to the CAGC pin of the device. To
maximize system range, it is important to keep the AGC
Micrel
January 18, 2005
Table 2. Sweep-Mode Recommended Reference Oscillator
T
is in MHz:
R
C
Values For Typical Transmit Frequencies
TH
433.92MHz
SC
TH
315MHz
390MHz
418MHz
is required to maximize range.
=
= 145Ω
R
τ
SC
9.7940
f
TH
T
TH
AGC
Capacitor
Capacitor
TH
12.140MHz
13.01MHz
13.51MHz
9.81MHz
and the on-chip
T
is in MHz:
TH
and C
(4)
(5)
AGC
8
control voltage ripple low, preferably under 10mV
the control voltage has attained its quiescent value. For
this reason, capacitor values of at least 0.47µF are
recommended.
The AGC control voltage is carefully managed on-chip to
allow duty-cycle operation of the MICRF009. When the
device is placed into shutdown mode (SHUT pin is pulled
high), the AGC capacitor floats to retain the voltage. When
operation is resumed, only the voltage droop due to
capacitor leakage must be replenished. A relatively low-
leakage capacitor is recommended when the devices are
used in duty-cycled operation.
To further enhance duty-cycled operation, the AGC push
and pull currents are boosted for approximately 10ms
immediately after the device is taken out of shutdown. This
compensates for AGC capacitor voltage droop and
reduces the time to restore the correct AGC voltage. The
current is boosted by a factor of 45.
Selecting CAGC Capacitor in Continuous Mode
A CAGC capacitor in the range of 0.47µF to 4.7µF is
typically recommended. Caution! If the capacitor is too
large, the AGC may react too slowly to incoming signals.
AGC settling time, from a completely discharged (zero-volt)
state is given approximately by Equation 6:
where:
Selecting CAGC Capacitor in Duty-Cycle Mode
Voltage droop across the CAGC capacitor during shutdown
should be replenished as quickly as possible after the IC is
enabled. As mentioned above, the MICRF009 boosts the
push-pull current by a factor of 45 immediately after start-
up. This fixed time period is based on the reference
oscillator frequency f
6.00MHz, and varies inversely with f
capacitor and the duration of the shutdown time period
should be selected such that the droop can be replenished
within this 10ms period.
Polarity of the droop is unknown, meaning the AGC voltage
could droop up or down. The worst-case from a recovery
standpoint is downward droop, since the AGC pull-up
current is 1/10th magnitude of the pull-down current. The
downward droop is replenished according to the Equation
7:
where:
C
I = AGC pull-up current for the initial 10ms (67.5µA)
AGC
∆t = 1.333 × C
C
AGC
I
is in µF, and ∆t is in seconds.
=
∆V
∆t
AGC
− 0.44
T
. The time is 10.9ms for f
T
. The value of CAGC
[phone]
M9999-011805
MICRF009
(6)
(7)
PP
once
T
=