LTC1448
Dual 12-Bit Rail-to-Rail
Micropower DAC
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DESCRIPTION
FEATURES
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The LTC®1448 is a dual rail-to-rail voltage output, 12-bit
digital-to-analog converter (DAC). It includes rail-to-rail
output buffer amplifiers and an easy-to-use 3-wire serial
interface. It is available in 8-pin SO and PDIP packages and
provides the smallest footprint of any dual 12-bit DAC.
SO-8 Package
12-Bit Resolution
Buffered True Rail-to-Rail Voltage Output
External Reference Input Can Be Tied to VCC
Output Swings from 0V to VREF
3V and 5V Supply Operation
Schmitt Trigger on Clock Input Allows Direct
Optocoupler Interface
Power-On Reset Clears DACs to 0V
3-Wire Serial Interface
Maximum DNL Error: 0.5LSB
Low Cost
The LTC1448 has an external reference input pin (REF)
and its outputs swing from 0V to REF. The REF input can
be tied to VCC providing rail-to-rail operation from supplies
of 2.7V to 5.5V. (For devices with internal reference see the
LTC1446 data sheet.) The LTC1448 dissipates 2.5mW
from a 5V supply.
The low power supply current and the small SO-8 package
make the LTC1448 ideal for battery-powered applications.
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APPLICATIONS
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Digital Calibration
Industrial Process Control
Automatic Test Equipment
Cellular Telephones
, LTC and LT are registered trademarks of Linear Technology Corporation.
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TYPICAL APPLICATION
Functional Block Diagram: 12-Bit Rail-to-Rail Dual DAC
Differential Nonlinearity
vs Input Code
2.7V TO 5.5V
0.5
7
4
REF
VCC
0.4
2 DIN
+
12-BIT
DAC B
µP
VOUT B 8
–
1 CLK
3 CS/LD
24-BIT
SHIFT
REG
AND
DAC
LATCH
RAIL-TO-RAIL
VOLTAGE
OUTPUTS
+
12-BIT
DAC A
DNL ERROR (LSB)
0.3
0.2
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
VOUT A 5
0
512 1024 1536 2048 2560 3072 3584 4095
CODE
1448 TA02
–
POWER-ON
RESET
GND
6
1448 TA01
1
LTC1448
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ABSOLUTE MAXIMUM RATINGS
PACKAGE/ORDER I FOR ATIO
VCC to GND .............................................. – 0.5V to 7.5V
Logic Inputs to GND ................................ – 0.5V to 7.5V
VOUT A, VOUT B, REF to GND ........... – 0.5V to VCC + 0.5V
Maximum Junction Temperature .......................... 125°C
Operating Temperature Range
LTC1448C ............................................ 0°C to 70°C
LTC1448I......................................... – 40°C to 85°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
TOP VIEW
CLK 1
8
VOUT B
DIN 2
7
VCC
CS/LD 3
6
GND
REF 4
5
VOUT A
N8 PACKAGE
8-LEAD PDIP
S8 PACKAGE
8-LEAD PLASTIC SO
LTC1448CN8
LTC1448IN8
LTC1448CS8
LTC1448IS8
S8 PART MARKING
TJMAX = 125°C, θJA = 100°C/W (N8)
TJMAX = 125°C, θJA = 150°C/W (S8)
1448
1448I
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
VCC = 2.7V to 5.5V, VOUT A and VOUT B unloaded, REF ≤ VCC, TA = TMIN to TMAX, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
DAC
Resolution
●
12
Bits
Monotonicity
●
12
Bits
DNL
Differential Nonlinearity
VREF ≤ VCC – 0.1V (Note 1)
●
INL
Integral Nonlinearity
VREF ≤ VCC – 0.1V (Note 1), TA = 25°C
VREF ≤ VCC – 0.1V (Note 1)
Measured at Code 20, TA = 25°C
Measured at Code 20
VOS
Offset Error
VOSTC
Offset Error Temperature
Coefficient
VFS
Full-Scale Voltage
VFSTC
± 0.2
± 0.5
LSB
●
± 5.0
± 5.5
LSB
LSB
●
± 10
± 15
mV
mV
±15
VREF = 4.096V, TA = 25°C
VREF = 4.096V
●
4.070
4.060
Full-Scale Voltage
Temperature Coefficient
4.095
4.095
µV/°C
4.120
4.130
10
V
V
ppm/°C
Power Supply
VCC
Positive Supply Voltage
For Specified Performance
●
ICC
Supply Current
(Note 4)
●
Short-Circuit Current Low
VOUT Shorted to GND
Short-Circuit Current High
2.7
5.5
V
450
700
µA
●
55
120
mA
VOUT Shorted to VCC
●
65
120
mA
Output Impedance to GND
Input Code = 0
●
30
120
Ω
Output Line Regulation
Input Code = 4095. VCC = 4.5V to 5.5V, VREF = 4.096V
●
0.2
1.5
LSB/V
Op Amp DC Performance
2
LTC1448
ELECTRICAL CHARACTERISTICS
VCC = 2.7V to 5.5V, VOUT A and VOUT B unloaded, REF ≤ VCC, TA = TMIN to TMAX, unless otherwise noted.
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
0.5
1.0
V/µs
14
µs
0.3
nV • s
AC Performance
Voltage Output Slew Rate
Voltage Output Settling Time
●
(Notes 2, 3) to ± 0.5LSB
Digital Feedthrough
Reference Input
RIN
REF Input Resistance
●
7.5
REF
REF Input Range
VIH
12.5
18
kΩ
(Notes 5, 6)
●
0
VCC
V
Digital Input High Voltage
VCC = 5V
VCC = 3V
●
●
2.4
2.0
VIL
Digital Input Low Voltage
VCC = 5V
VCC = 3V
●
●
0.8
0.6
V
V
ILEAK
Digital Input Leakage
VIN = GND to VCC
●
± 10
µA
CIN
Digital Input Capacitance
(Note 6)
●
10
pF
Digital I/O
V
V
Switching (VCC = 4.5V to 5.5V)
t1
DIN Valid to CLK Setup
t2
DIN Valid to CLK Hold
●
0
ns
t3
CLK High Time
(Note 6)
●
40
ns
t4
CLK Low Time
(Note 6)
●
40
ns
t5
CS/LD Pulse Width
(Note 6)
●
50
ns
t6
LSB CLK to CS/LD
(Note 6)
●
40
ns
t7
CS/LD Low to CLK
(Note 6)
●
20
ns
t8
CLK Low to CS/LD Low
(Note 6)
●
20
ns
●
60
ns
●
40
ns
Switching (VCC = 2.7V to 5.5V)
t1
DIN Valid to CLK Setup
t2
DIN Valid to CLK Hold
●
0
ns
t3
CLK High Time
(Note 6)
●
60
ns
t4
CLK Low Time
(Note 6)
●
60
ns
t5
CS/LD Pulse Width
(Note 6)
●
80
ns
t6
LSB CLK to CS/LD
(Note 6)
●
60
ns
t7
CS/LD Low to CLK
(Note 6)
●
30
ns
t8
CLK Low to CS/LD Low
(Note 6)
●
30
ns
The ● denotes specifications which apply over the full operating
temperature range.
Note 1: Nonlinearity is defined from code 20 to code 4095 (full scale).
See Applications Information.
Note 2: Load is 5k in parallel with 100pF.
Note 3: DAC switched between all 1s and the code corresponding to VOS
for the part.
Note 4: Digital inputs at 0V or VCC.
Note 5: VOUT can only swing from (GND + VOS) to (VCC – VOS) when
output is unloaded.
Note 6. Guaranteed by design, not subject to test.
3
LTC1448
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TYPICAL PERFORMANCE CHARACTERISTICS
Minimum Supply Headroom for
Full Output Swing vs Load Current
Differential Nonlinearity (DNL)
0.5
4
0.4
3
0.3
2
0.2
1
0
–1
–2
0.8
0.6
0.1
0
–0.1
0.5
0.4
0.3
–0.2
–3
–0.3
–4
–0.4
0.2
0.1
0
–0.5
–5
0
512 1024 1536 2048 2560 3072 3584 4095
CODE
∆VOUT < 1LSB
CODE: ALL 1’s
VOUT = 4.095V
0.7
VCC – VOUT (V)
5
DNL ERROR (LSB)
INL ERROR (LSB)
Integral Nonlinearity (INL)
0
512 1024 1536 2048 2560 3072 3584 4095
CODE
0
5
10
LOAD CURRENT (mA)
1448 G03
1448 TA02
1448 G01
Minimum Output Voltage vs
Output Sink Current
15
Supply Current vs
Logic Input Voltage
CODE: ALL 0’s
2.0
700
600
SUPPLY CURRENT (mA)
OUTPUT PULL-DOWN VOLTAGE (mV)
800
125°C
500
400
25°C
300
–55°C
200
1.6
1.2
0.8
0.4
100
0
0
0
5
10
OUTPUT SINK CURRENT (mA)
15
0
1
3
4
2
LOGIC INPUT VOLTAGE (V)
5
1448 G06
1448 G04
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PIN FUNCTIONS
CLK (Pin 1): Serial Interface Clock. Internal Schmitt trigger on this input allows direct optocoupler interface.
updating the DAC output and the CLK is disabled
internally.
DIN (Pin 2): Serial Interface Data. Data on the DIN pin is
latched into the shift register on the rising edge of the serial
clock.
REF (Pin 4): Reference Input for Both DACs. This pin can
be tied to VCC. The output will swing from 0V to REF. The
typical input resistance is 12.5k.
CS/LD (Pin 3): Serial Interface Enable and Load Control.
When CS/LD is low the CLK signal is enabled, so the data
can be clocked in. When CS/LD is pulled high, data is
loaded from the shift register into the DAC register,
VOUT A, VOUT B (Pins 5, 8): Buffered DAC Outputs.
4
GND (Pin 6): Ground.
VCC (Pin 7): Positive Supply Input. 2.7V ≤ VCC ≤ 5.5V.
Requires a bypass capacitor to ground.
LTC1448
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BLOCK DIAGRA
12-BIT
DAC B
LD
+
DAC B
REGISTER
CLK 1
8
VOUT B
7
VCC
6
GND
5
VOUT A
–
24-BIT
SHIFT
REGISTER
DIN 2
LD
CS/LD 3
DAC A
REGISTER
REF 4
12-BIT
DAC A
+
–
POWER-ON
RESET
1448 BD
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TI I G DIAGRA S
OPERATING SEQUENCE
DAC A INPUT
DAC B INPUT
MSB
LSB MSB
DIN
D11
D10
D9
D8
D7
D6
CLK
1
2
3
4
5
6
D5
7
D4
D3
8
9
D2
10
D1
11
D0
12
D11
LSB
D10
13
14
D9
15
D8
16
D7
D6
17
18
D5
19
D4
20
D3
21
D2
22
D1
D0
23
24
CS/LD
(UPDATE DAC OUTPUT)
(ENABLE CLOCK)
1448 TD01
t4
t3
t1
t2
t6
t7
CLK
t8
DIN
B0-B
PREVIOUS WORD
B11-A
MSB
B0-A
LSB
B11-B
MSB
B0-B
LSB
t5
CS/LD
1448 TD02
5
LTC1448
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DEFI ITIO S
Differential Nonlinearity (DNL): The differerence
between the measured change and the ideal 1LSB change
for any two adjacent codes. The DNL error between any
two codes is calculated as follows:
DNL = (∆VOUT – LSB)/LSB
where ∆VOUT is the measured voltage difference between
two adjacent codes.
Digital Feedthrough: The glitch that appears at the analog
output caused by AC coupling from the digital inputs when
they change state. The area of the glitch is specified in
(nV)(sec).
Full-Scale Error (FSE): The deviation of the actual fullscale voltage from ideal. FSE includes the effects of offset
and gain errors (see Applications Information).
Integral Nonlinearity (INL): The deviation from a straight
line passing through the endpoints of the DAC transfer
curve (Endpoint INL). Because the output cannot go below
zero, the linearity is measured between full scale and the
lowest code which guarantees the output will be greater
than zero. The INL error at a given input code is calculated
as follows:
INL = [VOUT – VOS – (VFS – VOS)(code/4095)]/LSB
where VOUT is the output voltage of the DAC measured at
the given input code.
Least Significant Bit (LSB): The ideal voltage difference
between two successive codes.
LSB = VREF/4096
Resolution (n): Defines the number of DAC output states
(2n) that divide the full-scale range. Resolution does not
imply linearity.
Voltage Offset Error (VOS): Nominally, the voltage at the
output when the DAC is loaded with all zeros. A single
supply DAC can have a true negative offset, but the output
cannot go below zero (see Applications Information).
For this reason, single supply DAC offset is measured at
the lowest code that guarantees the output will be greater
than zero.
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OPERATIO
Serial Interface
The data on the DIN input is loaded into the shift register
on the rising edge of the clock. Data is loaded as one 24bit word where the first 12 bits are for DAC A and the
second 12 are for DAC B. For each 12-bit segment the MSB
is loaded first. Data from the shift register is loaded into the
DAC register when CS/LD is pulled high. The clock is
disabled internally when CS/LD is high. Note: CLK must be
low before CS/LD is pulled low to avoid an extra internal
clock pulse.
Voltage Output
The LTC1448’s rail-to-rail buffered outputs can source or
sink 5mA over the entire operating temperature range
6
while pulling to within 300mV of the positive supply
voltage or ground. The output swings to within a few
millivolts of either supply rail when unloaded and has an
equivalent output resistance of 30Ω when driving a load to
the rails. The output can drive 1000pF without going into
oscillation.
The output swings from 0V to the voltage at the REF pin,
i.e., there is a gain of 1 from the REF to VOUT. Please note
if REF is tied to VCC the output can only swing to
(VCC – VOS). See Applications Information.
LTC1448
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APPLICATIONS INFORMATION
Rail-to-Rail Output Considerations
(FSE) is positive, the output for the highest codes limits at
VCC as shown in Figure 1c. No full-scale limiting can occur
if VREF is less than VCC – FSE.
In any rail-to-rail DAC, the output swing is limited to
voltages within the supply range.
Offset and linearity are defined and tested over the region
of the DAC transfer function where no output limiting can
occur.
If the DAC offset is negative, the output for the lowest
codes limits at 0V as shown in Figure 1b.
Similarly, limiting can occur near full scale when the REF
pin is tied to VCC. If VREF = VCC and the DAC full-scale error
VREF = VCC
POSITIVE
FSE
OUTPUT
VOLTAGE
INPUT CODE
(c)
VREF = VCC
OUTPUT
VOLTAGE
0
2048
INPUT CODE
4095
(a)
OUTPUT
VOLTAGE
0V
NEGATIVE
OFFSET
INPUT CODE
(b)
1448 F01
Figure 1. Effects of Rail-to-Rail Operation on a DAC Transfer Curve: (a) Overall Transfer Function, (b) Effect of Negative
Offset for Codes Near Zero Scale, (c) Effect of Positive Full-Scale Error for Input Codes Near Full Scale When VREF = VCC
7
LTC1448
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TYPICAL APPLICATIONS
This circuit shows how to use one LTC1448 to make an
autoranging ADC. The microprocessor sets the reference
span and the Common pin for the analog input by loading
the appropriate digital code into the LTC1448. VOUT A
controls the Common pin for the analog inputs to the
LTC1296 and VOUT B controls the reference span by setting
the REF + pin on the LTC1296. The LTC1296 has a Shutdown pin that goes low in shutdown mode. This will turn
off the PNP transistor supplying power to the LTC1448.
The resistor and capacitor on the LTC1448 outputs act as
a lowpass filter for noise.
An Autoranging 8-Channel ADC with Shutdown
22µF
+
5V
VCC
CH0
CS
DOUT
µP
CLK
8 ANALOG
INPUT CHANNELS
LTC1296
DIN
CH7
COM
SSO
REF +
REF –
74HC04
50k
50k
5V
0.1µF
CLK
VOUT B
DIN
VCC
100Ω
0.1µF
CS/LD
LTC1448
GND
100Ω
REF
1448 TA04
VOUT A
0.1µF
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LTC1448
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TYPICAL APPLICATIONS
Digitally Programmable Current Source
5V
0.1µF
CLK
µP
DIN
CS/LD
VCC
RL
REF
LTC1448
VS + 6V TO 100V
FOR RL ≤ 50Ω
VOUT A
DIN • 5
≈ 0mA TO 10mA
4096 • RA
+
LT1077
GND
IOUT =
Q1
2N3440
–
RA
510Ω
5%
VOUT B PIN NOT SHOWN FOR CLARITY
1448 TA05
9
LTC1448
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PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
N8 Package
8-Lead PDIP (Narrow 0.300)
(LTC DWG # 05-08-1510)
0.400*
(10.160)
MAX
8
7
6
5
1
2
3
4
0.255 ± 0.015*
(6.477 ± 0.381)
0.300 – 0.325
(7.620 – 8.255)
0.009 – 0.015
(0.229 – 0.381)
(
+0.035
0.325 –0.015
8.255
+0.889
–0.381
)
0.045 – 0.065
(1.143 – 1.651)
0.065
(1.651)
TYP
0.100 ± 0.010
(2.540 ± 0.254)
*THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.010 INCH (0.254mm)
10
0.130 ± 0.005
(3.302 ± 0.127)
0.125
(3.175) 0.020
MIN (0.508)
MIN
0.018 ± 0.003
(0.457 ± 0.076)
N8 1197
LTC1448
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PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
8
7
6
5
0.150 – 0.157**
(3.810 – 3.988)
0.228 – 0.244
(5.791 – 6.197)
1
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
0.053 – 0.069
(1.346 – 1.752)
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.014 – 0.019
(0.355 – 0.483)
2
3
4
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
TYP
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
SO8 0996
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LTC1448
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TYPICAL APPLICATION
12-Bit, 3V to 5V Supply, Dual Voltage Output DAC
2.7V TO 5.5V
0.1µF
DIN VCC
µP
CLK
REF
VOUT A
OUTPUT A
0V TO REF
VOUT B
OUTPUT B
0V TO REF
CS/LD
LTC1448
GND
1448 TA03
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC1257
Single 12-Bit VOUT DAC, Full Scale: 2.048V, VCC: 4.75V to 15.75V,
Reference Can Be Overdriven Up to 12V, i.e., FSMAX = 12V
5V to 15V Single Supply, Complete VOUT DAC in
SO-8 Package
LTC1446/LTC1446L
Dual 12-Bit VOUT DACs in SO-8 Package with Internal Reference
LTC1446: VCC = 4.5V to 5.5V, VOUT = 0V to 4.095V
LTC1446L: VCC = 2.7V to 5.5V, VOUT = 0V to 2.5V
LTC1450/LTC1450L
Single 12-Bit VOUT DACs with Parallel Interface
LTC1450: VCC = 4.5V to 5.5V, VOUT = 0V to 4.095V
LTC1450L: VCC = 2.7V to 5.5V, VOUT = 0V to 2.5V
LTC1451
Single Rail-to-Rail 12-Bit DAC, Full Scale: 4.095V, VCC: 4.5V to 5.5V,
Internal 2.048V Reference Brought Out to Pin
5V Low Power, Complete VOUT DAC in SO-8 Package
LTC1452
Single Rail-to-Rail 12-Bit VOUT Multiplying DAC, VCC: 2.7V to 5.5V
Low Power, Multiplying VOUT DAC with Rail-to-Rail
Buffer Amplifier in SO-8 Package
LTC1453
Single Rail-to-Rail 12-Bit VOUT DAC, Full Scale: 2.5V, VCC: 2.7V to 5.5V
3V, Low Power, Complete VOUT DAC in SO-8 Package
LTC1454/LTC1454L
Dual 12-Bit VOUT DACs in SO-16 Package with Added Functionality
LTC1454: VCC = 4.5V to 5.5V, VOUT = 0V to 4.095V
LTC1454L: VCC = 2.7V to 5.5V, VOUT = 0V to 2.5V
LTC1456
Single Rail-to-Rail Output 12-Bit DAC with Clear Pin,
Full Scale: 4.095V, VCC: 4.5V to 5.5V
Low Power, Complete VOUT DAC in SO-8
Package with Clear Pin
LTC1458/LTC1458L
Quad 12 Bit Rail-to-Rail Output DACs with Added Functionality
LTC1458: VCC = 4.5V to 5.5V, VOUT = 0V to 4.095V
LTC1458L: VCC = 2.7V to 5.5V, VOUT = 0V to 2.5V
LTC1659
Single Rail-to-Rail 12-Bit VOUT DAC in MSOP-8 Package,
VCC: 2.7V to 5.5V
Low Power Multiplying VOUT DAC in MSOP-8
Package. Output Swings from GND to REF.
REF Input Can Be Tied to VCC
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417● (408)432-1900
FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com
1448f LT/TP 0398 4K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1997
工商网监
湘ICP备2023018690号
