Micrel, Inc.

MICRF229

April 15, 2015

3

Revision 1.0

Pin Description (Continued)

Pin

Number

Pin

Name

Type

Pin Function

8

EN

Input

Enable Control Logic-Level Input: A logic-level HIGH enable the device. A logic-level LOW put

the device to shutdown mode. An internal pull-down (3µA typical) pulls the logic input LOW.

The device is designed to start up in shutdown state. The EN pin should be kept at logic low

(shutdown state) until after the supply voltage on VDD is stabilized. If the application is

designed to have the EN pin always pulled high, it is recommended to add a shunt capacitor of

0.47µF from the EN pin to ground.

9

GND

Supply

Ground Connection (for all chip functions except for RF input): Connect to PCB ground plane.

10

DO

In/Out

Demodulation Data Output: A current limited CMOS output in normal operation. An internal

pull-

down of 25kΩ is present when device is in shutdown. This pin is also used as the data

input during serial programming (see “Serial Interface Register Programming” sub-section).

11

SEL1

Input

Logic Control Input with Active Internal Pull-Up (3µA typical): It can be used to select the low-

pass filter bandwidth in the absence register control (see Table 2).

12

SCLK

Input

Programming clock input with active internal pull-down (3µA typical

13

CTH

In/Out

Demodulation Threshold Voltage Integration Capacitor: Capacitor to GND sets the settling

time for the demodulation data slice level. Values above 1nF are recommended and should be

optimized for data rate and data profile. Connect a 0.1µF capacitor from CTH pin to GND to

provide a stable slicing threshold.

14

AGC

In/Out

AGC Filter Capacitor Connection: Connect a capacitor from this pin to GND. Refer to the

“AGC Loop” sub-section for information on the capacitor value.

15

RSSI

Output

Received Signal Strength Indicator Output. The voltage on this pin is an inversed amplified

version of the voltage on AGC. Output is from a buffer with typically 200

Ω output impedance.

16

RO2

Output

Output of the Pierce Oscillator for Crystal: Internal capacitance of 7pF to GND during normal

operation.