MICRF219AAYQS TR Micrel Inc, MICRF219AAYQS TR Datasheet - Page 11

• Manufacturer Part Number: MICRF219AAYQS TR
• Description: IC RECEIVER QWIKRADIO 16QSOP
• Manufacturer: Micrel Inc
• Series: -r

Specifications of MICRF219AAYQS TR

• Frequency: 300MHz ~ 450MHz
• Sensitivity: -112.5dBm
• Data Rate - Maximum: -
• Modulation Or Protocol: ASK, OOK
• Applications: General Purpose
• Current - Receiving: 4.3mA
• Data Interface: PCB, Surface Mount
• Memory Size: -
• Antenna Connector: PCB, Surface Mount
• Features: RSSI Equipped
• Voltage - Supply: 3 V ~ 3.6 V
• Operating Temperature: -40°C ~ 105°C
• Package / Case: 16-SSOP (0.154", 3.90mm Width)
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: 576-3892-2; MICRF219AAYQSTR

Micrel, Inc.
The ability of the chip to track to a signal that
DECREASED in strength is much slower, since only
1.5μA is available to charge CAGC to increase the gain.
When designing a transmitter that communicates with
the MICRF219A, ensure that the power level remains
constant throughout the transmit burst.
The value of CAGC impacts the time to good data
(TTGD), which is defined as the time when signal is first
applied, to when the pulse width at DO is within 10% of
the steady state value. The optimal value of CAGC
depends on the setting of the D4 and D3 bits. A smaller
CAGC value does NOT always result in a shorter TTGD.
This is due to the loop dynamics, the fast discharge
current being 600µA, and the charge current being only
1.5µA. For example, if D4 = D3 = 0, the low pass filter
bandwidth is set to a minimum and CAGC capacitance is
too small, TTGD will be longer than if CAGC capacitance
is properly chosen. This is because when RF signal first
appears, the fast discharge period will reduce V
fast, lowering the gain of the mixer and IF amplifier. But
since the low pass filter bandwidth is low, it takes too
long for the AGC comparator to see a reduced level of
the audio signal, so it can not stop the discharge current.
This causes an undershoot in CAGC voltage and a
corresponding overshoot in RSSI voltage. Once CAGC
undershoots, it takes a long time for it to charge back up
because the current available is only 1.5µA.
Table 3 lists the recommended minimum CAGC values
for different D[4:3] settings to insure that the voltage on
CAGC does not undershoot. The recommendation also
takes into account the behavior in auto-polling. If CAGC
is too small, the chip can have a tendency to false wake
up (DO releases even when there is no input signal).
Figure 3 illustrates what occurs if CAGC capacitance is
too small for a given D[4:3] setting. Here, D[4:3] = 01,
the capacitance on CAGC pin is 0.47μF, and the RF
input level is stepped from no signal to −100dBm. RSSI
voltage is shown instead of CAGC voltage because
RSSI is a buffered version of CAGC (with an inversion
and amplification). Probing CAGC directly can affect the
loop dynamics through resistive loading from a scope
probe, especially in the state where only 1.5μA is
available, whereas probing RSSI does not. When RF
signal is first applied, RSSI voltage overshoots due to
July 2011
Table 3. Minimum Suggested CAGC Values
D4
0
0
1
1
D3
0
1
0
1
CAGC value
4.7μF
2.2μF
1μF
1μF
CAGC
very
11
the fast discharge current on CAGC, and the loop is too
slow to stop this fast discharge current in time. Since the
voltage on CAGC is too low, the audio signal level is
lower than the slicing threshold (voltage on CTH), and
DO pin is low. Once the fast discharge current stops,
only the small 1.5µA charge current is available in
settling the AGC loop to the correct level, causing the
recovery
condition to be slow. As a result, TTGD is about 9.1ms.
Figure 4 shows the behavior with a larger capacitor on
CAGC pin (2.2μF), D[4:3] = 01. In this case, V
not undershoot (RSSI does not overshoot), and TTGD is
relatively short at 1ms.
Figure 4. Proper TTGD (1ms) with Sufficient CAGC
Figure 3. RSSI Overshoot and Slow TTGD (9.1ms)
from
[e-mail]
CAGC
undershoot/RSSI
or [phone]
M9999-071811-A
MICRF219A
overshoot
CAGC
does