LTC1605C データシートの表示（PDF） - Linear Technology
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LTC1605C Datasheet PDF : 16 Pages
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LTC1605
APPLICATIONS INFORMATION
Internal Voltage Reference
The LTC1605 has an on-chip, temperature compensated,
curvature corrected, bandgap reference, which is factory
trimmed to 2.50V. The full-scale range of the ADC is equal
to (±4 • VREF) or nominally ±10V. The output of the
reference is connected to the input of a unity-gain buffer
through a 4k resistor (see Figure 3). The input to the buffer
or the output of the reference is available at REF (Pin 3).
The internal reference can be overdriven with an external
reference if more accuracy is needed. The buffer output
drives the internal DAC and is available at CAP (Pin 4). The
CAP pin can be used to drive a steady DC load of less than
2mA. Driving an AC load is not recommended because it
can cause the performance of the converter to degrade.
applied to VIN and R4 is adjusted until the output code is
changing between 0111 1111 1111 1110 and 0111 1111
1111 1111. Figure 6 shows the bipolar transfer character-
istic of the LTC1605.
±10V INPUT
200Ω
1%
33.2k
1%
+
2.2µF
1
2
VIN
AGND1
2.2µF
LTC1605
3 REF
4
CAP
5
AGND2
1605 • F04
Figure 4. ±10V Input Without Trim
REF
3
(2.5V)
4k
BANDGAP
REFERENCE
2.2µF
+
VANA
–
CAP
4
(2.5V)
2.2µF
INTERNAL
CAPACITOR
DAC
1605 • F03
Figure 3. Internal or External Reference Source
For minimum code transition noise the REF pin and the
CAP pin should each be decoupled with a capacitor to
filter wideband noise from the reference and the buffer
(2.2µF tantalum).
Offset and Gain Adjustments
The LTC1605 offset and full-scale errors have been trimmed
at the factory with the external resistors shown in Figure 4.
This allows for external adjustment of offset and full scale
in applications where absolute accuracy is important. See
Figure 5 for the offset and gain trim circuit. First adjust the
offset to zero by adjusting resistor R3. Apply an input
voltage of –152.6mV (– 0.5LSB) and adjust R3 so the code
is changing between 1111 1111 1111 1111 and 0000 0000
0000 0000. The gain error is trimmed by adjusting resistor
R4. An input voltage of 9.999542V (+FS – 1.5LSB) is
±10V INPUT
200Ω
1%
33.2k
1%
5V
R4
50k
R3
50k
1
2 VIN
AGND1
+ 2.2µF
3 REF
LTC1605
576k
+
4
CAP
2.2µF
5
AGND2
1605 • F05
Figure 5. ±10V Input with Offset and Gain Trim
011...111
011...110
000...001
000...000
111...111
111...110
BIPOLAR
ZERO
100...001
100...000
FS = 20V
1LSB = FS/65536
– FS/2
–1 0V 1
LSB LSB
INPUT VOLTAGE (V)
FS/2 – 1LSB
1605 • F06
Figure 6. LTC1605 Bipolar Transfer Characteristics
DC Performance
One way of measuring the transition noise associated with
a high resolution ADC is to use a technique where a DC
9
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