sm5170 Nippon Precision Circuits Inc, (NPC), sm5170 Datasheet - Page 7

• Manufacturer Part Number: sm5170
• Description: Pll Synthesizer Ic
• Manufacturer: Nippon Precision Circuits Inc, (NPC)

Reference Frequency Divider (R-counter) Structure
The reference frequency divider generates a comparator frequency signal (FR), which is input to the phase
comparator, by dividing the reference oscillator frequency input either from an external signal on XIN or from
a crystal oscillator connected between XIN and XOUT. The reference frequency divider is comprised of a fixed
divide-by-4 prescaler and a 16-bit reference counter.
Frequency settings
Counter set ranges
Reference frequency divider ratio range
Reference counter frequency data and LD setting
The reference counter which determines the reference frequency divider ratio is set by bits 1 to 16. The lock
detect signal output is set by bit 20.
Reference frequency divider example
If the VCO output is (f
parator frequency (f
Therefore, the reference counter count is 144 (0000000010010000)
LD output
The output on LD is set by bit 20.
Bit 20
1
0
Normal unlock signal output (normal operation)
Unlock signal output OFF, LOW-level output
MSB
1
2
15
2
2
14
R
)) is 25kHz, then the reference frequency divider ratio R is given by:
Prescaler
Reference counter
Reference frequency divider ratio
Prescaler
Reference counter
VCO
3
2
Reference Counter (16bit : 5 to 65535)
13
Figure 5. Reference counter data and LD output setting format
4
2
), the crystal oscillator frequency is 14.4MHz and the channel bandwidth (f
12
5
2
LD output
R =
11
Control bits
6
2
10
X’tal
f
7
2
Test bits (set to 00)
CH
9
8
2
8
=
9
2
7
LDpin Set bit
X’tal
f
10
2
R
6
11
SM5170AV
2
=
5
12
2
(0.025)
4
14.4
13
Not used (set to 000)
2
3
14
2
2
A (= 4)
B
R = A × B = 4 × B
A = 4
B = 5 to 65535
R = 20 to 262140
= 576 = 4 144
15
2
1
16
2
2
0
.
17
18
19
20
SEIKO NPC CORPORATION —7
21
22
23
LSB
24
CH
: com-