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DAC124S085 Datasheet(PDF) 16 Page - Texas Instruments

Part No. DAC124S085
Description  DAC124S085 12-Bit Micro Power Quad Digital-to-Analog Converter With Rail-to-Rail Output
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Maker  TI1 [Texas Instruments]
Homepage  http://www.ti.com
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DAC124S085 Datasheet(HTML) 16 Page - Texas Instruments

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DAC124S085
SNAS348G – MAY 2006 – REVISED APRIL 2016
www.ti.com
Product Folder Links: DAC124S085
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Copyright © 2006–2016, Texas Instruments Incorporated
Feature Description (continued)
8.3.4 Power-On Reset
The power-on reset circuit controls the output voltages of the four DACs during power-up. Upon application of
power, the DAC registers are filled with zeros and the output voltages are 0 V. The outputs remain at 0 V until a
valid write sequence is made to the DAC.
8.4 Device Functional Modes
8.4.1 Power-Down Modes
The DAC124S085 has four power-down modes, two of which are identical. In power-down mode, the supply
current drops to 20 µA at 3 V and 30 µA at 5 V. The DAC124S085 is set in power-down mode by setting OP1
and OP0 to 11. Because this mode powers down all four DACs, the address bits, A1 and A0, are used to select
different output terminations for the DAC outputs. Setting A1 and A0 to 00 or 11 causes the outputs to be tri-
stated (a high impedance state). While setting A1 and A0 to 01 or 10 causes the outputs to be terminated by 2.5
k
Ω or 100 kΩ to ground respectively (see Table 1).
Table 1. Power-Down Modes
A1
A0
OP1
OP0
OPERATING MODE
0
0
1
1
High-Z outputs
0
1
1
1
2.5 k
Ω to GND
1
0
1
1
100 k
Ω to GND
1
1
1
1
High-Z outputs
The bias generator, output amplifiers, resistor strings, and other linear circuitry are all shut down in any of the
power-down modes. However, the contents of the DAC registers are unaffected when in power down. Each DAC
register maintains its value prior to the ADC124S085 being powered down unless it is changed during the write
sequence which instructed it to recover from power down. Minimum power consumption is achieved in the
power-down mode with SYNC and DIN idled low and SCLK disabled. The time to exit power down (Wake-Up
Time) is typically tWU, which is stated in Timing Requirements.
8.5 Programming
8.5.1 Serial Interface
The three-wire interface is compatible with SPI, QSPI, and MICROWIRE, as well as most DSPs and operates at
clock rates up to 40 MHz. See Timing Requirements for information on a write sequence.
A write sequence begins by bringing the SYNC line low. Once SYNC is low, the data on the DIN line is clocked
into the 16-bit serial input register on the falling edges of SCLK. To avoid misclocking data into the shift register,
it is critical that SYNC not be brought low simultaneously with a falling edge of SCLK (see Figure 2). On the 16th
falling clock edge, the last data bit is clocked in and the programmed function (a change in the DAC channel
address, mode of operation, or register contents) is executed. At this point the SYNC line may be kept low or
brought high. Any data and clock pulses after the 16th falling clock edge are ignored. In either case, SYNC must
be brought high for the minimum specified time before the next write sequence is initiated with a falling edge of
SYNC.
Because the SYNC and DIN buffers draw more current when they are high, they must be idled low between write
sequences to minimize power consumption.
8.5.2 Input Shift Register
The input shift register, Figure 30, has sixteen bits. The first two bits are address bits. They determine whether
the register data is for DAC A, DAC B, DAC C, or DAC D. The address bits are followed by two bits that
determine the mode of operation (writing to a DAC register without updating the outputs of all four DACs, writing
to a DAC register and updating the outputs of all four DACs, writing to the register of all four DACs and updating
their outputs, or powering down all four outputs). The final twelve bits of the shift register are the data bits. The
data format is straight binary (MSB first, LSB last), with all 0s corresponding to an output of 0 V and all 1s
corresponding to a full-scale output of VREFIN – 1 LSB. The contents of the serial input register are transferred to
the DAC register on the sixteenth falling edge of SCLK (see Figure 2).


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