Datasheet
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Z
EFF
+
1
(2)(76.8kHz)(13fF)
+ 500MW
CLK_DETECT
Internal
Oscillator
MUX
ToADC
S
S0 S1
EN
Crystal
Oscillator
CLKIN/XTAL1
XTAL2
AVDD
(1) f
MOD
= 76.8kHz
Z
EFF
= 500M
Ω
(1)
VREFP VREFN
AVDD
ESD
Protection
C
BUF
CLOCK SOURCES
ADS1232
ADS1234
SBAS350F – JUNE 2005 – REVISED FEBRUARY 2008
Figure 29. Equivalent Circuitry of the Clock
Source
When the clock source is a crystal, simply connect
the 4.9152MHz crystal across the CLKIN/XTAL1 and
XTAL2 pins. Table 6 shows the recommended part
numbers. Due to the low-power design of the parallel
resonant driver circuitry onboard, both the
Figure 28. Simplified Reference Input Circuitry
CLKIN/XTAL1 and XTAL2 pins are only for use with
external crystals; they should not be used as clock
output drivers for external circuitry. No external
ESD diodes protect the reference inputs. To prevent
capacitors are used with the crystal; it is
these diodes from turning on, make sure the voltages
recommended to place the crystal close to the part in
on the reference pins do not go below GND by more
order to reduce board stray capacitance for both the
than 100mV, and likewise, do not exceed AVDD by
CLKIN/XTAL1 and XTAL2 pins and to insure proper
100mV:
operation.
GND – 100mV < (REFP or REFN) < AVDD + 100mV
Table 6. Recommended Crystals
MANUFACTURER FREQUENCY PART NUMBER
The ADS1232/4 can use an external clock source,
ECS 4.9152MHz ECS-49-20-1
external crystal, or internal oscillator to accommodate
ECS 4.9152MHz ECS-49-20-4
a wide variety of applications. Figure 29 shows the
equivalent circuitry of the clock source. The
CLK_DETECT block determines whether the crystal
An external oscillator may be used by driving the
oscillator/external clock signal is applied to the
CLKIN/XTAL1 pin directly. The Electrical
CLKIN/XTAL1 pin so that the internal oscillator is
Characteristics table shows the allowable frequency
bypassed or activated. When the CLKIN/XTAL1 pin
range.
frequency is above ~200kHz, the CLK_DETECT
output goes low and shuts down the internal
oscillator. When the XIN pin frequency is below
~200kHz, the CLK_DETECT output goes high and
activates the internal oscillator. It is highly
recommended to hard-wire the CLKIN/XTAL1 pin to
ground when the internal oscillator is chosen.
Copyright © 2005 – 2008, Texas Instruments Incorporated 15
Product Folder Link(s): ADS1232 ADS1234