MAX6909EO33 Maxim Integrated, MAX6909EO33 Datasheet - Page 12
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MAX6909EO33
Manufacturer Part Number
MAX6909EO33
Description
Real Time Clock
Manufacturer
Maxim Integrated
Series
MAX6909, MAX6910r
Datasheet
1.MAX6909EO33T.pdf
(33 pages)
Specifications of MAX6909EO33
Function
Clock, Calendar, Watchdog Timekeeper, NV SRAM Control
Rtc Bus Interface
Serial
Time Format
HH
Rtc Memory Size
31 B
Supply Voltage - Max
3.6 V
Supply Voltage - Min
3 V
Maximum Operating Temperature
+ 85 C
Minimum Operating Temperature
- 40 C
Mounting Style
SMD/SMT
Package / Case
QSOP-20
I
Supervisor and NV RAM Controller
Table 1. Crystal Manufacturers and Part Numbers
Timekeeping accuracy of the MAX6909/MAX6910 is
dependent on the frequency stability of the external
crystal. To determine frequency stability, use the para-
bolic curve of Figure 3 and the following equations:
where:
∆f = change in frequency from +25°C (Hz)
f = nominal crystal frequency (Hz)
k = parabolic curvature constant (-0.035 ±0.005ppm/°C
T
T = temperature of interest (°C)
For example: What is the worst-case change in oscilla-
tor frequency from +25°C ambient to +45°C ambient?
Figure 3. Frequency Stability and Temperature
12
Caliber Electronics
ECS INC International
Fox Electronics
M-tron
Raltron
0
2
= turnover temperature (+25°C ±5°C for 32.768kHz
for 32.768kHz watch crystals)
C-Compatible Real-Time Clocks with µP
______________________________________________________________________________________
watch crystals)
MANUFACTURER
-100
-150
-200
-250
-50
0
TYPICAL TEMPERATURE CHARACTERISTICS
-50
-40
(k = -0.035ppm/°C
∆f = f
-30
-20
-10
✕
TEMPERATURE (°C)
0
k
10
AWS2A-32.768KHz,
AWS2B-32.768KHz
ECS-.327-6.0-17
FSM327
SX2010/ SX2020
RSE-32.768-6-C-T
✕
20
(T
30
0
2
40
; T
- T)
50
O
= +25°C)
PART
60
2
70
80
90
100
2
RANGE (°C)
-20 to +70
-10 to +60
-40 to +85
-20 to +75
-10 to +60
TEMP
What is the worst-case timekeeping error per second?
1) Error due to temperature drift:
2) Error due to +25°C initial crystal tolerance of ±20ppm:
3) Total timekeeping error per second:
Figure 4. Oscillator Functional Schematic
∆t
∆t
∆t
drift
∆f
total
∆t
initial
∆t
initial
initial
{[1 / [(32,768Hz - 0.8192Hz) / 32,768]] - 1s} /
∆f
drift
= 0.000025s / s + 0.000020s / s = 0.000045 s / s
drift
= {[1 / [32,768 - 0.65536 / 32,768]] - 1} /
= 32,768Hz
12pF
= {[1 / [(f + ∆f
MAX6909
{[1 / [(f + ∆f
Cg
(20°C - 45°C)
= 32,768Hz
∆t
1s = 0.000025s / s
1s = 0.000020s / s
total
(pF)
C
6
6
6
6
6
L
= ∆t
X1
drift
✕
EXTERNAL
CRYSTAL
initial
(-20ppm) = -0.65536Hz
✕
drift
2
Rf
) / 32,768]] - 1s} / 1s
= -0.8192Hz
(-0.04ppm/°C)
) / 32,768]] - 1} / 1s
+ t
X2
+25°C FREQUENCY
TOLERANCE (ppm)
initial
±20
±20
±20
±20
±20
Rd
Cd
12pF
2
✕