MICRF505YML Micrel Inc, MICRF505YML Datasheet - Page 15

• Manufacturer Part Number: MICRF505YML
• Description: 433/915MHZ ITRANSCEIVER, SMD, MLF32
• Manufacturer: Micrel Inc

Specifications of MICRF505YML

• Transmitting Current: 28mA
• Data Rate: 200Kbps
• Frequency Range: 850MHz To 950MHz
• Modulation Type: FSK
• Sensitivity Dbm: -111dBm
• Rf Ic Case Style: MLF
• No. Of Pins: 32
• Supply Voltage Range: 2V To 2.5V
• Output Power: 10dBm
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Charge Pump
The charge pump current can be set to either 125mA or 500mA
by CP_HI (‘1’ D 500mA). This will affect the loop filter compo-
nent values, see “PLL Filter” section. In most cases, the
lowest current is best suited. For applications using a high
phase detector frequency and a high PLL bandwidth, the
500mA can be a better choice.
PLL Filter
The design of the PLL filter will strongly affect the perfor-
mance of the frequency synthesizer. The PLL filter is kept
externally for flexibility. Input parameters when designing the
loop filter for the MICRF505 are mainly the modulation
method and the bit rate. These choices will also affect the
switching time and phase noise.
The frequency modulation can be done in two different ways
with the MICRF505, either by VCO modulation or by modu-
lation with the internal dividers (see chapter Frequency
modulation for further details). In the first case, the PLL
bandwidth needs to be adequately low not to cancel the
modulation. In the second case, using the dividers, the PLL
needs to lock on a new carrier frequency for every new data
bit. Now the PLL bandwidth needs to be adequately high. It
may be necessary to use a third order filter to suppress the
phase detector frequency, as this is not suppressed as much
as when doing modulation on the VCO.
May 13, 2004
MICRF505
A6..A0
0000011
VCO
VCO
Internal
CP_HI
D7
(kbaud/sec)
Baud Rate
D6
‘0’
>125
>20
>10
D5
‘0’
D4
‘0’
PLL BW
(kHz)
0.8
12
3
OUTS3 OUTS2 OUTS1 OUTS0
D3
Margin (
Table 9. Loop Filter Components Values
Phase
D2
56
56
65
∞
D1
)
Detector Freq. (kHz)
D0
15
Phase
500
500
300
A schematic for a second and third order loop filter is shown
in Figure 5. For a second order filter, C3 is not connected and
R2 is 0 W.
Table 9 shows three different loop filters, the two first for VCO
modulation and the last one for modulation using the internal
dividers. The component values are calculated with RF
frequency = 915MHz, VCO gain = 67MHz/V and charge
pump current = 125mA. Other settings are shown in the table.
The varactor pin capacitance (pin 29) of 6pF does not
influence on the component values for the two filters with
lowest bandwidth. For the 12kHz bandwidth filter, a third
order loop filter is calculated. The third pole is set by R2¥C3.
Here C3 is chosen to be 6pF, the same as the varactor input
pin capacitance (pin 29). C3 can therefore be skipped.
Figure 8. Second and Third Order Loop Filter
CP_OUT
Pin 27
3.9nF
56nF
56nF
C1
560nF
560nF
560pF
C1
C2
R1
C2
1.2kW
4.7kW
R2
27kW
R1
C3
220kW
R2
0
0
M9999-051304
VARIN
Pin 29
NC
NC
NC
C3
Micrel