MICRF112_13 datasheet(13/21 Pages) MICREL

13 / 21 page

Micrel, Inc.

MICRF112

February 2013

M9999-020713

Application Information

Figure 4. ASK 433.92MHz and 315MHz (MSOP)

Note: Values in parenthesis are for 315MHz.

The MICRF112 is ideal for driving a 50

Ω source

monopole or a loop antenna. Figure 4 is an example of a

loop antenna configuration. Figure 4 also shows both

315MHz and 433.92MHz ASK configurations for a loop

antenna. In addition to using a different crystal, modified

values are needed for certain frequencies. These are

listed in Table 1.

Frequency

(MHz)

(nH)

(pF)

(nH)

(pF)

(MHz)

315.0

470

150

6.8

9.84375

433.92

680

4.7

13.5600

Table 1. Modified Frequency Values

The reference design shown in Figure 4 has an antenna

optimized for using the matching network, as described

in Table 1.

Power Control Using an External Resistor

R7 is used to adjust the RF output levels that may be

needed to meet compliance. As an example, Tables 2

and 3 list typical values of conducted RF output levels

and corresponding R7 resistor values for the 50

Ω test

board shown in the Test Circuit.

R7,

Ω

Output Power, dBm

IDD, mA

6.7

8.5

6.3

100

8.0

6.2

500

1.6

4.13

1000

−3.8

4.87

Table 2. ASK Output Power at 1Kbps (Manchester) vs.

External Resistor at 315MHz

R7,

Ω

Output Power, dBm

IDD, mA

8.68

7.5

8.34

7.33

100

8.02

7.3

500

4.34

6.3

1000

0.42

5.5

Table 3. ASK Output Power at 1Kbps (Manchester) vs.

External Resistor at 433.92MHz

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