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LTC2327-18 数据表(PDF) 13 Page - Linear Technology

部件名 LTC2327-18
功能描述  True Bipolar, Pseudo-Differential Input ADC with 95dB SNR
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制造商  LINER [Linear Technology]
网页  http://www.linear.com
标志 LINER - Linear Technology

LTC2327-18 数据表(HTML) 13 Page - Linear Technology

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LTC2327-18
13
232718fa
For more information www.linear.com/LTC2327-18
applicaTions inForMaTion
Figure 5a. LTC2327-18 Internal Reference Circuit
Table 1. Internal Reference with Internal Buffer
REFIN
REFBUF
BIPOLAR INPUT RANGE
2.048V
4.096V
±10.24V
Table 2. External Reference with Internal Buffer
REFIN
(OVERDRIVE)
REFBUF
BIPOLAR INPUT RANGE
1.25V (Min)
2.5V
±6.25V
2.048V
4.096V
±10.24V
2.4V (Max)
4.8V
±12V
Table 3. External Reference Unbuffered
REFIN
REFBUF
(OVERDRIVE)
BIPOLAR INPUT RANGE
0V
2.5V (Min)
±6.25V
0V
5V (Max)
±12.5V
Internal Reference with Internal Buffer
The LTC2327-18 has an on-chip, low noise, low drift
(20ppm/°C max), temperature compensated bandgap
reference that is factory trimmed to 2.048V. It is internally
connected to a reference buffer as shown in Figure 5a and
is available at REFIN (Pin 8). REFIN should be bypassed to
GNDwitha100nFceramiccapacitortominimizenoise.The
reference buffer gains the REFIN voltage by 2 to 4.096V at
REFBUF (Pin 7). So the input range is ±10.24V, as shown
in Table 1. Bypass REFBUF to GND with at least a 47μF
ceramic capacitor (X7R, 10V, 1210 size) to compensate
the reference buffer and minimize noise.
External Reference with Internal Buffer
If more accuracy and/or lower drift is desired, REFIN
can be easily overdriven by an external reference since
a 15k resistor is in series with the reference as shown
in Figure 5b. REFIN can be overdriven in the range from
1.25V to 2.4V. The resulting voltage at REFBUF will be
2 • REFIN. So the input range is ±5 • REFIN, as shown
in Table 2. Linear Technology offers a portfolio of high
performance references designed to meet the needs of
manyapplications.Withitssmallsize,lowpower,andhigh
accuracy, the LTC6655-2.048 is well suited for use with
the LTC2327-18 when overdriving the internal reference.
The LTC6655-2.048 offers 0.025% (max) initial accuracy
and 2ppm/°C (max) temperature coefficient for high pre-
cision applications. The LTC6655-2.048 is fully specified
over the H-grade temperature range and complements
the extended temperature range of the LTC2327-18 up to
125°C.BypassingtheLTC6655-2.048witha2.7μFto100µF
ceramic capacitor close to the REFIN pin is recommended.
External Reference Unbuffered
The internal reference buffer can also be overdriven from
2.5V to 5V with an external reference at REFBUF as shown
in Figure 5c. So the input ranges are ±6.25V to ±12.5V,
respectively, as shown in Table 3. To do so, REFIN must
be grounded to disable the reference buffer. A 13k resis-
tor loads the REFBUF pin when the reference buffer is
disabled. To maximize the input signal swing and cor-
responding SNR, the LTC6655-5 is recommended when
overdrivingREFBUF.TheLTC6655-5offersthesamesmall
size, accuracy, drift and extended temperature range as
the LTC6655-2.048. By using this 5V reference, an SNR
of 97dB can be achieved. Bypassing the LTC6655-5 with
a 47μF ceramic capacitor (X5R, 0805 size) close to the
REFBUF pin is recommended.
TheREFBUFpinoftheLTC2327-18drawsacharge(QCONV)
fromtheexternalbypasscapacitorduringeachconversion
cycle. If the internal reference buffer is overdriven, the
external reference must provide all of this charge with a
DC current equivalent to IREFBUF = QCONV/tCYC. Thus, the
DC current draw of REFBUF depends on the sampling
LTC2327-18
BANDGAP
REFERENCE
232718 F05a
47µF
100nF
6.5k
REFBUF
REFIN
15k
6.5k
REFERENCE
BUFFER
GND


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