Specifications

ST72104Gx, ST72215Gx, ST72216Gx, ST72254Gx
110/141
CLOCK CHARACTERISTICS (Cont’d)
13.5.4 RC Oscillators
The ST7 internal clock can be supplied with an RC
oscillator. This oscillator can be used with internal
or external components (selectable by option
byte).
Figure 66. Typical Application with RC oscillator
Figure 67. Typical Internal RC Oscillator Figure 68. Typical External RC Oscillator
Notes:
1. Data based on characterization results.
2. Guaranteed frequency range with the specified C
EX
and R
EX
ranges taking into account the device process variation.
Data based on design simulation.
3. Data based on characterization results done with V
DD
nominal at 5V, not tested in production.
4. R
EX
must have a positive temperature coefficient (ppm/°C), carbon resistors should therefore not be used.
5. Important: when no external C
EX
is applied, the capacitance to be considered is the global parasitic capacitance which
is subject to high variation (package, application...). In this case, the RC oscillator frequency tuning has to be done by
trying out several resistor values.
Symbol Parameter Conditions Min Typ Max Unit
f
OSC
Internal RC oscillator frequency
1)
see Figure 67 3.60 5.10
MHz
External RC oscillator frequency
2)
1 14
t
SU(OSC)
Internal RC Oscillator Start-up Time
3)
2.0
ms
External RC Oscillator Start-up Time
3)
R
EX
=47KΩ, C
EX
=”0”pF
R
EX
=47KΩ, C
EX
=100pF
R
EX
=10KΩ, C
EX
=6.8pF
R
EX
=10KΩ, C
EX
=470pF
1.0
6.5
0.7
3.0
R
EX
Oscillator external resistor
4)
see Figure 68
10 47 KΩ
C
EX
Oscillator external capacitor 0
5)
470 pF
OSC2
OSC1
f
OSC
C
EX
R
EX
EXTERNAL RC
INTERNAL RC
V
REF
+
-
V
DD
Current copy
Voltage generator
C
EX
discharge
ST72XXX
3.2 5.5
VDD [V]
3.8
3.9
4
4.1
4.2
4.3
fosc [ MH z]
-40°C
+25°C
+85°C
+125°C
0 6.8 22 47 100 270 470
Cex [pF]
0
5
10
15
20
fosc [MHz]
Rex=10KOhm
Rex=15KOhm
Rex=22KOhm
Rex=33KOhm
Rex=39KOhm
Rex=47KOhm