參數(shù)資料
型號: DC1783A-G
廠商: Linear Technology
文件頁數(shù): 2/24頁
文件大小: 0K
描述: BOARD SAR ADC LTC2377-18
軟件下載: QuikEval II System
設(shè)計(jì)資源: DC1783A Design Files
DC1783A Schematic
標(biāo)準(zhǔn)包裝: 1
系列: QuikEval™
ADC 的數(shù)量: 1
位數(shù): 18
采樣率(每秒): 500k
數(shù)據(jù)接口: 串行,SPI?
輸入范圍: ±VREF
在以下條件下的電源(標(biāo)準(zhǔn)): 6.8mW @ 500kSPS
工作溫度: 0°C ~ 70°C
已用 IC / 零件: LTC2377-18
已供物品:
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LTC2377-18
10
237718f
OVERVIEW
The LTC2377-18 is a low noise, low power, high speed 18-bit
successive approximation register (SAR) ADC. Operating
from a single 2.5V supply, the LTC2377-18 supports a
large and flexible ±VREF fully differential input range with
VREF ranging from 2.5V to 5.1V, making it ideal for high
performance applications which require a wide dynamic
range. The LTC2377-18 achieves ±1.75LSB INL max, no
missing codes at 18 bits and 102dB SNR.
Fast 500ksps throughput with no cycle latency makes
the LTC2377-18 ideally suited for a wide variety of high
speed applications. An internal oscillator sets the con-
version time, easing external timing considerations. The
LTC2377-18 dissipates only 6.8mW at 500ksps, while an
auto power-down feature is provided to further reduce
power dissipation during inactive periods.
The LTC2377-18 features a unique digital gain compres-
sion (DGC) function, which eliminates the driver amplifier’s
negative supply while preserving the full resolution of the
ADC. When enabled, the ADC performs a digital scaling
function that maps zero-scale code from 0V to 0.1 VREF
and full-scale code from VREF to 0.9 VREF. For a typical
reference voltage of 5V, the full-scale input range is now
0.5V to 4.5V, which provides adequate headroom for
powering the driving amplifier from a single 5.5V supply.
CONVERTER OPERATION
The LTC2377-18 operates in two phases. During the ac-
quisition phase, the charge redistribution capacitor D/A
converter (CDAC) is connected to the IN+ and INpins to
sample the differential analog input voltage. A rising edge
on the CNV pin initiates a conversion. During the conversion
phase, the 18-bit CDAC is sequenced through a succes-
sive approximation algorithm, effectively comparing the
sampled input with binary-weighted fractions of the refer-
ence voltage (e.g. VREF/2, VREF/4 … VREF/262144) using
the differential comparator. At the end of conversion, the
CDAC output approximates the sampled analog input. The
ADC control logic then prepares the 18-bit digital output
code for serial transfer.
APPLICATIONS INFORMATION
Figure 2. LTC2377-18 Transfer Function
INPUT VOLTAGE (V)
0V
OUTPUT
CODE
(TWO’S
COMPLEMENT)
–1
LSB
237718 F02
011...111
011...110
000...001
000...000
100...000
100...001
111...110
1
LSB
BIPOLAR
ZERO
111...111
FSR/2 – 1LSB
–FSR/2
FSR = +FS – –FS
1LSB = FSR/262144
TRANSFER FUNCTION
The LTC2377-18 digitizes the full-scale voltage of 2
× REF
into 218 levels, resulting in an LSB size of 38μV with
REF = 5V. The ideal transfer function is shown in Figure 2.
The output data is in 2’s complement format.
RON
40Ω
CIN
45pF
RON
40Ω
REF
CIN
45pF
IN+
IN
BIAS
VOLTAGE
237718 F03
Figure 3. The Equivalent Circuit for the
Differential Analog Input of the LTC2377-18
ANALOG INPUT
The analog inputs of the LTC2377-18 are fully differential
in order to maximize the signal swing that can be digitized.
The analog inputs can be modeled by the equivalent circuit
shown in Figure 3. The diodes at the input provide ESD
protection. In the acquisition phase, each input sees ap-
proximately 45pF (CIN) from the sampling CDAC in series
with 40Ω (RON) from the on-resistance of the sampling
switch. Any unwanted signal that is common to both
inputs will be reduced by the common mode rejection of
the ADC. The inputs draw a current spike while charging
the CIN capacitors during acquisition. During conversion,
the analog inputs draw only a small leakage current.
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