参数资料
型号: THS5641IPWR
厂商: TEXAS INSTRUMENTS INC
元件分类: DAC
英文描述: PARALLEL, 8 BITS INPUT LOADING, 0.035 us SETTLING TIME, 8-BIT DAC, PDSO28
封装: PLASTIC, TSSOP-28
文件页数: 9/29页
文件大小: 725K
代理商: THS5641IPWR
THS5641
8-BIT, 100 MSPS, CommsDAC
DIGITAL-TO-ANALOG CONVERTER
SLAS199A – MAY 1999 REVISED JUNE 1999
17
POST OFFICE BOX 655303
DALLAS, TEXAS 75265
APPLICATION INFORMATION
analog current outputs
Figure 26 shows a simplified schematic of the current source array output with corresponding switches.
Differential PMOS switches direct the current of each individual PMOS current source to either the positive
output node IOUT1 or its complementary negative output node IOUT2. The output impedance is determined
by the stack of the current sources and differential switches, and is typically >300 k
in parallel with an output
capacitance of 5 pF.
Output nodes IOUT1 and IOUT2 have a negative compliance voltage of –1 V, determined by the CMOS process.
Beyond this value, transistor breakdown may occur, resulting in reduced reliability of the THS5641 device. The
positive output compliance depends on the full-scale output current IOUTFS and positive supply voltage AVDD.
The positive output compliance equals 1.25 V for AVDD = 5 V and IOUTFS = 20 mA. For AVDD = 3.3 V the output
compliance is limited to 0.6 V. Exceeding the positive compliance voltage adversely affects distortion
performance and integral nonlinearity. The optimum distortion performance for a single-ended or differential
output is achieved when the maximum full-scale signal at IOUT1 and IOUT2 does not exceed 0.5 V (e.g. when
applying a 50
doubly terminated load for 20 mA full-scale output current). Applications requiring the THS5641
output (i.e., OUT1 and/or OUT2) to extend its output compliance should size RLOAD accordingly.
AVDD
Current Source Array
IOUT1
IOUT2
RLOAD
Current
Sources
Switches
Figure 26. Equivalent Analog Current Output
Figure 27(a) shows the typical differential output configuration with two matched externally resistor loads. The
nominal resistor load of 50
will give a differential output swing of 2 VPP when applying a 20 mA full-scale output
current. The output impedance of the THS5641 depends slightly on the output voltage at nodes IOUT1 and
IOUT2. Consequently, for optimum dc integral nonlinearity, the configuration of Figure 27(b) should be chosen.
In this I–V configuration, terminal IOUT1 is kept at virtual ground by the inverting operational amplifier. The
complementary output should be connected to ground to provide a dc current path for the current sources
switched to IOUT2. Note that the INL/DNL specifications for the THS5641 are measured with IOUT1 maintained
at virtual ground. The amplifier’s maximum output swing and the DAC’s full-scale output current determine the
value of the feedback resistor RFB. Capacitor CFB filters the steep edges of the THS5641 current output, thereby
reducing the operational amplifier slew-rate requirements. In this configuration, the op amp should operate on
a dual supply voltage due to its positive and negative output swing. Node IOUT1 should be selected if a
single-ended unipolar output is desirable.
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