The MC145181 is a dual frequency synthesizer containing very–low supply voltage circuitry. The device supports two independent loops with a single input reference and operates down to 1.8 V. Phase noise reduction circuitry is incorporated into the device.

The MC145181 operates up to 550 MHz on the main loop and up to 60 MHz on the secondary loop. The device has a 32/33 prescaler for the main loop. Lock detection circuitry for both loops is multiplexed to a single output.

Two 8–bit DACs are powered through a dedicated pin. The DAC supply range is 1.8 to 3.6 V; this voltage may differ from the main supply.

• Operating Frequency

   Main Loop: 100 to 550 MHz

   Secondary Loop: 10 to 60 MHz

• Operating Supply Voltage: 1.8 to 3.6 V

• Nominal Supply Current, Both Loops Active: 3 mA

• Maximum Standby Current, All Systems Shut Down: 10 µA

• Phase Detector Output Current:

   1.8 V Supply — PDout–Hi: 2.8 mA, PDout–Lo: 0.7 mA

   ≥2.5 V Supply — PDout–Hi: 4.4 mA, PDout–Lo: 1.1 mA

• Two Independent 8–Bit DACs with Separate Supply Pin (Up to 3.6 V)

• Lock Detect Output with Adjustable Lock Indication Window

• Independent R Counters Allow Independent Step Sizes for Each Loop

• Main Loop Divider Range: 992 to 262,143

• Secondary Loop Divider Range: 7 to 8,191

• Fractional Reference Counters Divider Range: 20 to 32,767.5

• Auxiliary Reference Divider with Small–Signal Differential

   Output — Ratios: 8, 10, 12.5

• Three General–Purpose Outputs

• Direct Interface to Motorola SPI Data Port Up to 10 Mbps