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參數(shù)資料
| 型號： | LTC1668CG |
| 廠商： | LINEAR TECHNOLOGY CORP |
| 元件分類： | DAC |
| 英文描述： | Replaced by TLV5617A : 10-Bit Dual DAC 8-SOIC |
| 中文描述： | PARALLEL, WORD INPUT LOADING, 0.02 us SETTLING TIME, 16-BIT DAC, PDSO28 |
| 封裝： | 5.30 MM, PLASTIC, SSOP-28 |
| 文件頁數(shù)： | 6/16頁 |
| 文件大?。?/td> | 728K |
| 代理商： | LTC1668CG |
6
LTC1668
APPLICATIOU
Theory of Operation
The LTC1668 is a high speed current steering 16-Bit DAC
made on an advanced BiCMOS process. Precision thin
film resistors and well matched bipolar transistors result
in excellent DC linearity and stability. A low glitch current
switching design gives excellent AC performance at sample
rates up to 50Msps. The device is complete with a 2.5V
internal bandgap reference and edge triggered latches,
and sets a new standard for DAC applications requiring
very high dynamic range at output frequencies up to
several megahertz.
Referring to the Block Diagram, the DAC contains an array
of current sources that are steered to I
OUTA
or I
OUTB
with
NMOS differential current switches. The four most signifi-
cant bits, DB15 to DB12 are made up of 15 current
segments of equal weight. The lower bits, DB11 to DB0 are
binary weighted, using a combination of current scaling
and a differential resistive attenuator ladder. All bits and
segments are precisely matched, both in current weight
for DC linearity, and in switch timing for low glitch impulse
and low spurious tone AC performance.
W
U
U
Setting the Full-Scale Current, I
OUTFS
The full-scale DAC output current, I
OUTFS
, is nominally
10mA, and can be adjusted down to 1mA. Placing a
resistor, R
SET
, between the REFOUT pin, and the I
REFIN
pin
sets I
OUTFS
as follows.
The internal reference control loop amplifier maintains a
virtual ground at I
REFIN
by servoing the internal current
source, I
INT
, to sink the exact current flowing into I
REFIN
.
I
INT
is a scaled replica of the DAC current sources and
I
OUTFS
= 8 (I
INT
), therefore:
I
OUTFS
= 8 (I
REFIN
) = 8 (V
REF
/R
SET
)
For example, if R
SET
= 2k and is tied to V
REF
= REFOUT =
2.5V, I
REFIN
= 2.5/2k = 1.25mA and I
OUTFS
= 8 (1.25mA)
= 10mA.
The reference control loop requires a capacitor on the
COMP1 pin for compensation. For optimal AC perfor-
mance, C
COMP1
should be connected to V
SS
and be placed
very close to the package (less than 0.1").
(1)
For fixed reference voltage applications, C
COMP1
should
be 0.1
μ
F or more. The reference control loop small-signal
bandwidth is approximately 1/(2
π
) C
COMP1
80 or 20kHz
for C
COMP1
= 0.1
μ
F.
Internal Reference Output—REFOUT
The onboard 2.5V bandgap voltage reference drives the
REFOUT pin. It is trimmed and specified to drive a 2k
resistor tied from REFOUT to I
REFIN
, corresponding to a
1.25mA load (I
OUTFS
= 10mA). REFOUT has nominal
output impedance of 6
, or 0.24% per mA, so it must be
buffered to drive any additional external load. A 0.1
μ
F
capacitor is required on the REFOUT pin for compensa-
tion. Note that this capacitor is required for stability, even
if the internal reference is not being used.
DAC Transfer Function
The LTC1668 uses straight binary digital coding. The
complementary current outputs, I
OUT A
and I
OUT B
, sink
current from 0 to I
OUTFS
. For I
OUTFS
= 10mA (nominal),
I
OUT A
swings from 0mA when all bits are low (i.e., Code =
0) to 10mA when all bits are high (i.e., Code = 65535) (deci-
mal representation). I
OUT B
is complementary to I
OUT A
.
I
OUT A
and I
OUT B
are given by the following formulas:
I
OUT A
= I
OUTFS
(DAC Code/65536)
I
OUT B
= I
OUTFS
(65535-DAC Code)/65536
In typical applications, the LTC1668 differential output
currents either drive a resistive load directly or drive an
equivalent resistive load through a transformer, or as the
feedback resistor of an I-to-V converter. The voltage
outputs generated by the I
OUT A
and I
OUT B
output currents
are then:
V
OUT A
= I
OUT A
R
LOAD
V
OUT B
= I
OUT B
R
LOAD
The differential voltage is:
V
DIFF
= V
OUT A
– V
OUT B
= (I
OUT A
– I
OUT B
) (R
LOAD
)
(2)
(3)
(4)
(5)
(6)
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| LTC1668I | Replaced by TLV5617A : 10-Bit Dual DAC 8-SOIC |
| LTC1669 | Replaced by TLV5617A : 10-Bit, 2.5 us Dual DAC, Serial Input, Pgrmable Settling Time, Simultaneous Update, Low Power 8-SOIC 0 to 70 |
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