FM4005
Layout Requirements
The X1 and X2 crystal pins employ very high
impedance circuits and the oscillator connected to
these pins can be upset by noise or extra loading. To
reduce RTC clock errors from signal switching noise,
a guard ring must be placed around these pads and
the guard ring grounded. SDA and SCL traces should
be routed away from the X1/X2 pads. The X1 and X2
trace lengths should be less than 5 mm. The use of a
ground plane on the backside or inner board layer is
preferred. See layout example. Red is the top layer,
green is the bottom layer.
VDD
SCL
SDA
X2
X1
PFI
VBAK
VDD
SCL
SDA
X2
X1
PFI
VBAK
Layout for Surface Mount Crystal
(red = top layer, green = bottom layer)
Layout for Through Hole Crystal
(red = top layer, green = bottom layer)
Calibration Adjustments
Positive Calibration for slow clocks: Calibration will achieve +/- 2.17 PPM after calibration
Measured Frequency Range
Error Range (PPM)
Min
Max
Min
Max
Program Calibration Register to:
512.0000
511.9989
0
2.17
000000
511.9989
511.9967
2.18
6.51
100001
511.9967
511.9944
6.52
10.85
100010
511.9944
511.9922
10.86
15.19
100011
511.9922
511.9900
15.20
19.53
100100
511.9900
511.9878
19.54
23.87
100101
511.9878
511.9856
23.88
28.21
100110
511.9856
511.9833
28.22
32.55
100111
511.9833
511.9811
32.56
36.89
101000
511.9811
511.9789
36.90
41.23
101001
511.9789
511.9767
41.24
45.57
101010
511.9767
511.9744
45.58
49.91
101011
511.9744
511.9722
49.92
54.25
101100
511.9722
511.9700
54.26
58.59
101101
511.9700
511.9678
58.60
62.93
101110
511.9678
511.9656
62.94
67.27
101111
511.9656
511.9633
67.28
71.61
110000
511.9633
511.9611
71.62
75.95
110001
511.9611
511.9589
75.96
80.29
110010
511.9589
511.9567
80.30
84.63
110011
511.9567
511.9544
84.64
88.97
110100
511.9544
511.9522
88.98
93.31
110101
511.9522
511.9500
93.32
97.65
110110
511.9500
511.9478
97.66
101.99
110111
511.9478
511.9456
102.00
106.33
111000
511.9456
511.9433
106.34
110.67
111001
511.9433
511.9411
110.68
115.01
111010
511.9411
511.9389
115.02
119.35
111011
511.9389
511.9367
119.36
123.69
111100
511.9367
511.9344
123.70
128.03
111101
511.9344
511.9322
128.04
132.37
111110
511.9322
511.9300
132.38
136.71
111111
0
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Rev. 2.3
Oct. 2006
Page 8 of 23
RAMTRON [ RAMTRON INTERNATIONAL CORPORATION ]
