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參數資料
| 型號： | AD7740KRM |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 模擬專用變換器 |
| 英文描述： | 3 V/5 V Low Power, Synchronous Voltage-to-Frequency Converter |
| 中文描述： | VOLTAGE-FREQUENCY CONVERTER, 1 MHz, PDSO8 |
| 封裝： | MICRO, SOIC-8 |
| 文件頁數： | 7/11頁 |
| 文件大小： | 144K |
| 代理商： | AD7740KRM |
AD7740
REV. 0
–7–
GENERAL DESCRIPTION
The AD7740 is a CMOS synchronous Voltage-to-Frequency
Converter (VFC) which uses a charge-balance conversion
technique. The input voltage signal is applied to a proprietary
front-end based around an analog modulator which converts the
input voltage into an output pulse train.
The part also contains an on-chip 2.5 V bandgap reference and
operates from a single 3.3 V or 5 V supply. A block diagram of
the AD7740 is shown in Figure 3.
VIN
INTEGRATOR
FOUT
COMPARATOR
BUF
GND
SWITCHED
CAPS
SWITCHED
CAPS
AD7740
Figure 3. Block Diagram
Input Amplifier Buffering and Voltage Range
The analog input VIN can be buffered by setting BUF = 1. This
presents a high impedance, typically 100 M
, which allows
significant external source impedances to be tolerated. The VIN
voltage range is now 0.1 V to VDD – 0.2 V. By setting BUF = 0
the AD7740 input circuit accepts an analog input below GND
and the analog input VIN has a voltage range from –0.15 V to
VDD + 0.15 V. In this case the input impedance is typically
650 k
.
The transfer function for the AD7740 is represented by:
FOUT
= 0.1
f
CLKIN
+ 0.8 (
VIN/V
REF
)
f
CLKIN
It is shown in Figure 4 for unbuffered mode.
V
REF
OUTPUT
FREQUENCY
FOUT
V
REF
+ 0.15V
0.10 f
CLKIN
FOUT MIN
INPUT
VOLTAGE
VIN
FOUT MAX
0.90 f
CLKIN
0
–
0.15V
AD7740
Figure 4. Transfer Function
Sample Calculation:
V
REF
= 2.5 V, BUF = 0
FOUT (min) = 0.1 f
CLKIN
+ 0.8(–0.15/2.5) f
CLKIN
= 0.052 f
CLKIN
FOUT (max) = 0.1 f
CLKIN
+ 0.8(2.65/2.5) f
CLKIN
= 0.948 f
CLKIN
VFC Modulator
The analog input signal to the AD7740 is continuously sampled
by a switched capacitor modulator whose sampling rate is set
by a master clock. The input signal may be buffered on-chip
(BUF = 1) before being applied to the sampling capacitor of the
modulator. This isolates the sampling capacitor charging currents
from the analog input pin.
This system is a negative feedback loop that acts to keep the net
charge on the integrator capacitor at zero, by balancing charge
injected by the input voltage with charge injected by V
REF
. The
output of the comparator provides the digital input for the 1-bit
DAC, so that the system functions as a negative feedback loop
that acts to minimize the difference signal. See Figure 5.
INTEGRATOR
COMPARATOR
1-BIT
BITSTREAM
+V
REF
INPUT
CLK
–
V
REF
AD7740
Figure 5. Modulator Loop
The digital data that represents the analog input voltage is con-
tained in the duty cycle of the pulse train appearing at the output
of the comparator. The output is a pulse train whose frequency
depends on the analog input signal. A full-scale input gives an
output frequency of 0.9 f
CLKIN
and zero-scale input gives an
output frequency of 0.1 f
CLKIN
. The output allows simple inter-
facing to either standard logic families or opto-couplers. The
pulsewidth of FOUT is fixed and is determined by the high period
of CLKIN. The pulse is synchronized to the rising edge of the
clock signal. The delay time between the edge of CLKIN and the
edge of FOUT is typically
35
ns. Figure 6 shows the waveform
of this frequency output. (See TPC 8.)
3
t
CLKIN
FOUT = f
CLKIN
/2
VIN = V
REF
/2
f
CLKIN
FOUT = f
CLKIN
/5
VIN = V
REF
/8
FOUT = f
3/10
VIN = V
REF
/4
4t
CLKIN
AVERAGE FOUT IS f
3/10 BUT THE ACTUAL PULSE STREAM VARIES
BETWEEN f
CKLIN
/3 and f
CKLIN
/4
Figure 6. Frequency Output Waveforms
If there is a step change in input voltage, there is a settling time
that must elapse before valid data is obtained. This is typically
two CLKIN cycles.
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相關代理商/技術參數 |
參數描述 |
|---|---|
| AD7740KRM-REEL | 制造商:Analog Devices 功能描述:VFC Sync 1MHz 8-Pin MSOP T/R 制造商:Analog Devices 功能描述:VFC SYNC 1MHZ 8MSOP - Tape and Reel |
| AD7740KRM-REEL7 | 功能描述:IC CONVERTER V TO FREQ 8-MSOP RoHS:否 類別:集成電路 (IC) >> PMIC - V/F 和 F/V 轉換器 系列:- 標準包裝:1 系列:- 類型:頻率至電壓 頻率 - 最大:10kHz 全量程:- 線性:±0.3% 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 供應商設備封裝:8-SOIC 包裝:Digi-Reel® 其它名稱:LM2917MX-8/NOPBDKR |
| AD7740KRMZ | 功能描述:IC CONV SYNC VOLT-FREQ 8-MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - V/F 和 F/V 轉換器 系列:- 標準包裝:1 系列:- 類型:頻率至電壓 頻率 - 最大:10kHz 全量程:- 線性:±0.3% 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 供應商設備封裝:8-SOIC 包裝:Digi-Reel® 其它名稱:LM2917MX-8/NOPBDKR |
| AD7740KRMZ | 制造商:Analog Devices 功能描述:Voltage / Frequency (V/F & F/V) Converte |
| AD7740KRMZ-REEL | 功能描述:IC CONVERTER VOLT TO FREQ 8MSOP RoHS:是 類別:集成電路 (IC) >> PMIC - V/F 和 F/V 轉換器 系列:- 標準包裝:1 系列:- 類型:頻率至電壓 頻率 - 最大:10kHz 全量程:- 線性:±0.3% 安裝類型:表面貼裝 封裝/外殼:8-SOIC（0.154"，3.90mm 寬） 供應商設備封裝:8-SOIC 包裝:Digi-Reel® 其它名稱:LM2917MX-8/NOPBDKR |
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