LTC1427-50
Micropower, 10-Bit Current
Output DAC with SMBus
Serial Interface
FEATURES
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DESCRIPTION
The LTC
®
1427-50 is a micropower, 10-Bit current output
DAC with an output range of 0µA to 50µA. The DAC output is
guaranteed monotonic and DNL is less than 0.9LSB under all
operating conditions. Full-scale accuracy is
±2.5%
over
the commercial temperature range. The LTC1427-50 oper-
ates with power supply voltages from 2.7V to 5.5V and the
DAC current source output can be biased from (V
CC
– 1.3V)
to – 15V.
The LTC1427-50 communicates with external circuitry by
using the SMBus serial interface. It acts as an SMBus slave
device using one of four selectable SMBus addresses set by
the two address pins AD0 and AD1 .
On power-up, the DAC output assumes midrange or zero
scale, depending on the logic state of the two address pins.
The LTC1427-50 can be shut down through the SHDN pin or
by setting the SHDN bit = 1 in the SMBus command byte.
Digital data for the DAC output is retained internally and the
supply current drops to 10µA typically when in shutdown.
The LTC1427-50 is available in an 8-pin SO package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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Precision 50
µ
A,
±
1.5% Initial Full-Scale Output
Current,
±
2.5% Over Temperature
Wide Output Voltage DC Compliance: – 15V to
(V
CC
– 1.3V)
Wide Supply Range: 2.7V
≤
V
CC
≤
5.5V
Supply Current in Shutdown: 10µA Typ
Low Supply Current: 115µA Typ
Available in 8-Pin SO
SMBus Serial Interface
Four Selectable SMBus Addresses
DAC Powers Up at Zero or Midscale
DAC Contents Are Retained in Shutdown
APPLICATIONS
s
s
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LCD Contrast and Backlight Brightness Control
Power Supply Voltage Adjustment
Battery Charger Voltage/Current Adjustment
GaAs FET Bias Adjustment
Trimmer Pot Elimination
TYPICAL APPLICATION
Digitally Controlled LCD Bias Generator
L1
D1
V
OUT
*
6
V
IN
2 TO 4
CELLS
SHDN
1µF
3
LT1317
SHDN
GND
4
FB
V
C
1
4700pF
100k
5
SW
2
R2
12.1k
1%
C1
1µF
R1
226k
1%
LTC1427-50
1
2
3
4
SHDN
AD1
AD0
GND
V
CC
I
OUT
SCL
SDA
8
7
6
5
µPU
(e.g., 8051)
P1.2
P1.1
P1.0
L1 = 10
µH
SUMIDA CD43
MURATA-ERIE LQH3C
OR COILCRAFT DO1608
D1 =MBR0530
*V
OUT
= 12.7V TO 24V IN 11mV STEPS
15mA (2 CELLS)
35mA ( 3 CELLS)
U
U
U
V
CC
3.3V
1427 TA02
1
LTC1427-50
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
SHDN 1
AD1 2
AD0 3
GND 4
8
7
6
5
V
CC
I
OUT
SCL
SDA
Total Supply Voltage (V
CC
) ........................................ 7V
Input Voltage (All Inputs)............. – 0.3V to (V
CC
+ 0.3V)
DAC Output Voltage ...................... – 15V to (V
CC
+ 0.3V)
DAC Output Short-Circuit Duration .................. Indefinite
Operating Ambient Temperature Range ....... 0°C to 70°C
Junction Temperature .......................................... 125°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec.)................. 300°C
ORDER PART
NUMBER
LTC1427CS8-50
S8 PART MARKING
14275
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 125°C,
θ
JA
= 190°C/ W
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
SYMBOL
V
CC
I
CC
PARAMETER
Supply Voltage
Supply Current
DAC Resolution
I
FS
I
ZS
DNL
DAC Full-Scale Current
DAC Zero-Scale Current
DAC Differential Nonlinearity
Supply Voltage Rejection
Output Voltage Rejection
I
IN
V
IH
Logic Input Current
High Level Input Voltage
CONDITIONS
T
A
= operating temperature range unless otherwise specified.
MIN
q
TYP
115
10
10
MAX
5.5
225
25
50.75
51.25
±200
±0.9
±8
±5
±1
UNITS
V
µA
µA
Bits
µA
µA
nA
LSB
LSB
LSB
µA
V
V
V
2.7
V
SHDN
= V
SCL
= V
SDA
= V
CC
= 3.3V
V
SHDN
= 0V
V
CC
= 3.3V, V(I
OUT
) = 0V
q
q
q
q
49.25
48.75
50
50
±0.1
±0.15
V
CC
= 3.3V, V(I
OUT
) = 0V
V
CC
= 3.3V, Monotonicity Guaranteed, V(I
OUT
) = 0V
V
CC
= 2.7V to 5.5V, V(I
OUT
) = 0V
V
CC
= 3.3V, Full-Scale Current, – 15V
≤
V(I
OUT
)
≤
2V
0V
≤
V
IN
≤
V
CC
AD0, AD1
SHDN
SCL, SDA
SHDN, AD0, AD1
SCL, SDA
I
OUT
= 3mA, SDA Only
q
q
q
q
q
q
q
q
q
q
q
V
CC
– 0.3
2.4
1.4
0.8
0.6
0.4
V
IL
V
OL
Low Level Input Voltage
Low Level Output Voltage
2
U
W
U
U
W W
W
V
V
V
LTC1427-50
RECO
SYMBOL
f
SMB
t
BUF
t
HD:STA
t
SU:STA
t
SU:STO
t
HD:DAT
t
SU:DAT
t
LOW
t
HIGH
t
f
t
r
E DED OPERATI G CO DITIO S
CONDITIONS
q
q
q
q
q
q
q
q
q
q
q
V
CC
= 3.3V, T
A
= operating temperature range unless otherwise specified.
PARAMETER
SMB Operating Frequency
Bus Free Time Between Stop and Start Condition
Hold Time After (Repeated) Start Condition
Repeated Start Condition Setup Time
Stop Condition Setup Time
Data Hold Time
Data Setup Time
Clock Low Period
Clock High Period
Clock/Data Fall Time
Clock/Data Rise Time
MIN
10
4.7
4.0
4.7
4.0
300
250
4.7
4.0
50
300
1000
TYP
MAX
100
UNITS
kHz
µs
µs
µs
µs
ns
ns
µs
µs
ns
ns
SMBus Timing (Notes 2, 3)
The
q
denotes specifications that apply over the full operating temperature
range.
Note 1:
Absolute Maximum Ratings are those beyond which the life of the
device may be impaired.
Note 2:
All values are referenced to V
IH
and V
IL
levels.
Note 3:
These parameters are guaranteed by design and are not tested.
Refer to the Timing Diagrams for additional information.
TYPICAL PERFORMANCE CHARACTERISTICS
DNL vs Code
1.0
6
4
0.5
DNL (LSB)
INL (LSB)
0
–0.5
–1.0
0
512
CODE
1024
1247 G01
U
U
U
U W
U WW
INL vs Code
2
0
–2
–4
–6
–8
–10
0
512
CODE
1024
1247 G02
3
LTC1427-50
TYPICAL PERFORMANCE CHARACTERISTICS
Zero-Scale Current vs
Temperature
0.02
0
–0.02
OUTPUT CURRENT (µA)
OUTPUT CURRENT (µA)
–0.04
–0.06
–0.08
–0.10
–0.12
–0.14
–0.16
V (I
OUT
) = 0V
–0.18
–50 –25
0
25 50 75 100 125
TEMPERATURE (°C)
Bias Voltage Rejection
(Zero-Scale Current)
4
ZERO-SCALE OUTPUT CURRENT (nA)
FULL-SCALE OUTPUT ERROR (LSB)
T
A
= 25°C
V
CC
= 3.3V
2
1.0
0
–2
–4
–15 –12
0
I
OUT
BIAS VOLTAGE (V)
–9
–6
Supply Voltage Rejection
2
FULL-SCALE OUTPUT ERROR (LSB)
T
A
= 25°C
V(I
OUT
) = 0V
200
SHUTDOWN CURRENT (µA)
SUPPLY CURRENT (µA)
1
0
–1
–2
0
1
5
SUPPLY VOLTAGE (V)
2
3
4
4
U W
–3
6
1427 G07
Full-Scale Current vs
Temperature
52
V(I
OUT
) = 0V
51
50
49
150
48
–50 –25
0
25
50
75
100 125
150
TEMPERATURE (°C)
1427 G04
1427 G03
Bias Voltage Rejection
(Full-Scale Current)
T
A
= 25°C
V
CC
= 3.3V
0.5
0
–0.5
3
6
–1.0
–15 –12
0
I
OUT
BIAS VOLTAGE (V)
–9
–6
–3
3
6
1427 G05
1427 G06
Supply Current vs Temperature
20
Shutdown Current vs Temperature
150
V
CC
= 5.5V
V
CC
= 3.3V
15
V
CC
= 5.5V
10
V
CC
= 2.7V
5
V
CC
= 3.3V
V
CC
= 2.7V
100
50
7
0
–50 –25
0
25 50 75 100 125
TEMPERATURE (°C)
150
0
–50 –25
0
25 50 75 100 125
TEMPERATURE (°C)
150
1527 G08
1527 G09
LTC1427-50
PIN FUNCTIONS
SHDN (Pin 1):
Shutdown. A logic low puts the chip into
shutdown mode. In shutdown, the digital settings for the
DAC are retained. On release from shutdown, the previ-
ously programmed value for I
OUT
is reinstated.
AD1, AD0 (Pins 2, 3):
Address Selection Pins. Tie these
two pins to either V
CC
or GND to select one of four SMBus
addresses to which the LTC1427-50 will respond.
GND (Pin 4):
Ground. Ground should be tied directly to a
ground plane.
SDA (Pin 5):
SMBus Bidirectional Data Input/Digital Out-
put. This pin is an open-drain output and requires a pull-
up resistor or current source to V
CC
. Data is shifted into the
SDA pin and acknowledged by the SDA pin.
SCL (Pin 6):
SMBus Clock Input. Data is shifted into the
SDA pin at the rising edges of the SCL clock during data
transfer.
I
OUT
(Pin 7):
DAC Current Output.
V
CC
(Pin 8):
Voltage Supply. This supply must be kept free
from noise and ripple by bypassing directly to the ground
plane.
FU CTIO TABLES
AD1
L
L
H
H
AD0
L
H
L
H
SMBus Address Location
0101101
0101111
0101110
0101100
DAC Power-Up Value
Zero-Scale
Zero-Scale
Zero-Scale
Midscale
Application
CCFL Backlight Control
General Purpose
General Purpose
LCD Contrast Control
BLOCK DIAGRAM
SCL
SDA
SMBUS
INTERFACE
AD0
W
U
U
U
U
U
SHDN
SD
POWER-ON
RESET
3
REGISTER A
3-BIT
LATCH
EN1
1
REGISTER B
1-BIT LATCH
EN2
SHDN
VOLTAGE
REFERENCE
SD
R
ADJ
2
8
REGISTER C
10-BIT
LATCH
10
EN2
SD
10-BIT
CURRENT
DAC
I
OUT
AD1
1427 BD
5
微控制器 MCU
