MICRF007

Micrel

MICRF007

8

December 2000

achievable duty ratios. Push-pull currents are increased by

45 times their nominal values. The fixed time period is based

on the reference oscillator frequency f

6.00MHz, and varies inversely as f

Reference Oscillator

All timing and tuning operations on the MICRF007 are de-

rived from the internal Colpitts reference oscillator. Timing

and tuning is controlled through the REFOSC pin in one of two

ways:

1. Connect a crystal

2. Drive this pin with an external timing signal

The multiplication factor between the reference oscillator

frequency f

f

The second approach is attractive for lowering system cost

further if an accurate reference signal exists elsewhere in the

system, for example, a reference clock from a crystal-con-

trolled microprocessor. An externally applied signal should

be ac-coupled and resistively-attenuated, or otherwise lim-

ited, to approximately 0.5Vpp. The specific reference fre-

quency required is related to the system transmit frequency.

Shutdown Function

The shutdown function is controlled by a logic state applied

to the SHUT pin. When V

low-power standby mode, consuming less than 1

µA. This pin

is pulled high internally. It must be externally pulled low to

enable the receiver.