1VOUT Voltage Output Terminal" />
參數(shù)資料
型號: AD7845KRZ-REEL
廠商: Analog Devices Inc
文件頁數(shù): 9/12頁
文件大?。?/td> 0K
描述: IC DAC 12BIT MULT LC2MOS 24-SOIC
產(chǎn)品培訓(xùn)模塊: Data Converter Fundamentals
DAC Architectures
標(biāo)準(zhǔn)包裝: 1,000
設(shè)置時間: 5µs
位數(shù): 12
數(shù)據(jù)接口: 并聯(lián)
轉(zhuǎn)換器數(shù)目: 1
電壓電源: 雙 ±
功率耗散(最大): 150mW
工作溫度: 0°C ~ 70°C
安裝類型: 表面貼裝
封裝/外殼: 24-SOIC(0.295",7.50mm 寬)
供應(yīng)商設(shè)備封裝: 24-SOIC W
包裝: 帶卷 (TR)
輸出數(shù)目和類型: 1 電壓,單極;1 電壓,雙極
采樣率(每秒): 200k
AD7845
REV. B
–6–
PIN FUNCTION DESCRIPTION (DIP)
Pin
Mnemonic
Description
1VOUT
Voltage Output Terminal
2-11
DB11–DB2
Data Bit 11 (MSB) to Data Bit 2
12
DGND
Digital Ground. The metal lid on the ceramic package is connected to this pin
13-14
DB1–DB0
Data Bit 1 to Data Bit 0 (LSB)
15
WR
Write Input. Active low
16
CS
Chip Select Input. Active low
17
VREF
Reference Input Voltage which can be an ac or dc signal
18
AGND
Analog Ground. This is the reference point for external analog circuitry
19
VSS
Negative power supply for the output amplifier (nominal –12 V to +15 V)
20
VDD
Positive power supply (nominal +12 V to +15 V)
21
RA
Application resistor. RA = 4 RFB
22
RB
Application resistor. RB = 2 RFB
23
RC
Application resistor. RC = 2 RFB
24
RFB
Feedback resistor in the DAC. For normal operation this is connected to VOUT
CIRCUIT INFORMATION
Digital Section
Figure 11 is a simplified circuit diagram of the AD7845 input
control logic. When
CS and WR are both low, the DAC latch is
loaded with the data on the data inputs. All the digital inputs
are TTL, HCMOS and +5 V CMOS compatible, facilitating
easy microprocessor interfacing. All digital inputs incorporate
standard protection circuitry.
Figure 11. AD7845 Input Control Logic
D/A Section
Figure 12 shows a simplified circuit diagram for the AD7845
D/A section and output amplifier.
A segmented scheme is used whereby the 2 MSBs of the 12-bit
data word are decoded to drive the three switches A-C. The
remaining 10 bits drive the switches (S0–S9) in a standard R-2R
ladder configuration.
R
RR
2R
BA
S9
2R
C
VREF
S8
S0
SHOWN FOR ALL 1s ON DAC
2R
IOUT
AGND
Figure 12. Simplified Circuit Diagram for the AD7845 D/A
Section
Each of the switches A–C steers 1/4 of the total reference cur-
rent with the remaining 1/4 passing through the R-2R section.
An output amplifier and feedback resistor perform the current-
to-voltage conversion giving
VOUT = – D
× V
REF
where D is the fractional representation of the digital word. (D
can be set from 0 to 4095/4096.)
The amplifier can maintain
±10 V across a 2 k load. It is inter-
nally compensated and settles to 0.01% FSR (1/2 LSB) in less
than 5
s. The input offset voltage is laser trimmed at wafer
level. The amplifier slew rate is typically 11 V/
s, and the unity
gain small signal bandwidth is 600 kHz. There are three extra
on-chip resistors (RA, RB, RC) connected to the amplifier invert-
ing terminal. These are useful in a number of applications in-
cluding offset adjustment and gain ranging.
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