Datasheet

LM4050-4.1
DAC161S055
SDI
SCLK
CSB
V
OUT
0.47 PF
9V
Battery
R
V
Z
SDO
4.5V
Battery
(3 AA)
VREF
VA
LM4120-
4.096
DAC161S055
SDI
SCLK
CSB
V
OUT
= 0V to 4.095V
C1
0.1 PF
C2
0.022 PF
Input
Voltage
SDO
VREF VA
C3
0.022 PF
DAC161S055
www.ti.com SNAS503B –NOVEMBER 2010–REVISED JANUARY 2012
APPLICATIONS INFORMATION
SAMPLE INSTRUCTION SEQUENCE
The following table shows an example instruction sequence to illustrate the usage of different modes of operation
of the DAC. This sequence is for a one channel DAC.
Step Instruction 8-bit Command 16 bit Payload Comments
1 CLR 0000 0001 0000 0000 0000 0000 Clear device - return to Power-Up Default State
Write 1/4 FS into channel 0. Since device by default is in
2 WR 0000 1000 0100 0000 0000 0000 WRITE-BLOCK mode the data will be written into PREREG,
and DAC output will not update
Issue LDAC command to channel 0. Data is transferred from
3 LDAC 0001 1000 xxxx xxxx 0000 0001
PREREG into DACREG and DAC output updates to 1/4 FS
Set channels 1 to 7 to WRITE-BLOCK mode, and channel 0 to
4 SWB 0010 1000 xxxx xxxx 1111 1110
WRITE-THROUGH mode
DAC output updates immediately to FS since the channel is
5 WR 0000 1000 1111 1111 1111 1111
set to write through mode.
Power down the device, and set the channel 0 DAC output to
6 PD 0011 0000 0000 0001 0000 0000
the HIZ state
USING REFERENCES AS POWER SUPPLIES
Although the DAC has a separate reference and analog power pin, it is still possible to use a reference to drive
both. This arrangement will avoid a separate voltage regulator for V
A
and will provide a more stable voltage
source. The LM4140 has an initial accuracy of 0.1%, is capable of driving 8mA and comes in a 4.096V version.
Bypassing both the input and the output will improve noise performance.
Figure 23. Using the LM4120 as a power supply
A LOW NOISE EXAMPLE
A LM4050 powered off of a battery is a good choice for very low noise prototype circuits. The minimum value for
R must be chosen so that the LM4050 does not draw more than its 15mA rating. Note the largest current through
the LM4050 will occur when the DAC is shutdown. The maximum resistor value must allow the LM4050 to draw
more than its minimum current for regulation plus the maximum V
REF
current.
Figure 24. Using the LM4050 in a low noise circuit
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