BU2618FV Datasheet, PDF (6/8 Pages) Rohm – PLL frequency synthesizer for tuners

Audio ICs
S Frequency counter
(1) Structure
BU2618FV
(2) How the frequency counter operates
When control data CT equals 1, the 20-bit counter
and the amp go into operation. When CT equals 0,
amp input goes to pulldown and the counter is re-
set. Measuring time (gate pulse) is selected
(16ms / 32ms) on the basis of control data GT.
When control data CT equals 0, the counter is reset.
(3) Explanation of output data
D0: LSB D19: MSB
Unlock detection
When control data GT equals 1, or CT equals 1, the
unlock detection circuit goes into operation for 8 ms.
When CT equals 1, the unlock detection circuits
stops operating before the frequency counter gate
pulse is emitted. When CT equals 0, or GT equals
0, the unlock detection circuit is reset.
144