Final Electrical Specifications
LT1790-2.5
2.5V Micropower SOT-23
Low Dropout Reference
March 2000
FEATURES
s
DESCRIPTIO
s
s
s
s
s
s
High Accuracy:
A Grade—0.05% Max
B Grade—0.1% Max
Low Drift:
A Grade—10ppm/
°
C Max
B Grade—25ppm/
°
C Max
Low Supply Current: 60µA Max
Sinks and Sources: 5mA Min
Low Dropout Voltage
Guaranteed Operational –40°C to 125°C
Wide Supply Range: 2.6V to 18V
The LT
®
1790-2.5 is a SOT-23 micropower low dropout
series reference that combines high accuracy and low drift
with low power dissipation and small package size. This
micropower reference uses curvature compensation to
obtain a low temperature coefficient and trimmed preci-
sion thin-film resistors to achieve high output accuracy. In
addition, the LT1790-2.5 uses post-package trimming to
greatly reduce the temperature coefficient and increase
the output accuracy. Output accuracy is further assured by
excellent line and load regulation. Special care has been
taken to minimize thermally induced hysteresis.
The LT1790-2.5 is ideally suited for battery-operated
systems because of its small size, low supply current and
reduced dropout voltage. This reference provides supply
current and power dissipation advantages over shunt
references that must idle the entire load current to operate.
However, since the LT1790-2.5 can also sink current, it
can operate as a micropower negative voltage reference
with the same performance as a positive reference.
, LTC and LT are registered trademarks of Linear Technology Corporation.
APPLICATIO S
s
s
s
s
s
Handheld Instruments
Negative Voltage References
Industrial Control Systems
Data Acquisition Systems
Battery-Operated Equipment
TYPICAL APPLICATIO
Typical V
OUT
Distribution
50
45
167 UNITS
NUMBER OF UNITS
Positive Connection
2.6V
≤
V
IN
≤
18V
0.1µF
4
LT1790-2.5
1, 2
6
1µF
1790 TA01
40
35
30
25
20
15
10
5
0
2.498
V
OUT
= 2.5V
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
U
LT1790BC LIMITS
LT1790AC LIMITS
2.499 2.500
2.501
OUTPUT VOLTAGE (V)
2.502
1790 TA02
U
U
1
LT1790-2.5
ABSOLUTE
MAXIMUM
RATINGS
(Note 1)
PACKAGE/ORDER INFORMATION
TOP VIEW
GND 1
GND 2
DNC* 3
6 V
OUT
5 DNC*
4 V
IN
Input Voltage .......................................................... 20V
Specified Temperature Range ..................... 0°C to 70°C
Operating Temperature Range
(Note 2) ........................................... – 40°C to 125°C
Storage Temperature Range
(Note 3) ........................................... – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
ORDER PART
NUMBER
LT1790ACS6-2.5
LT1790BCS6-2.5
S6 PART MARKING
LTMX
LTMZ
S6 PACKAGE
6-LEAD PLASTIC SOT-23
T
JMAX
= 150°C,
θ
JA
= 230°C/W
*DNC: DO NOT CONNECT
Consult factory for Industrial and Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER
Output Voltage (Notes 3, 4)
The
q
denotes specifications that apply over the specified temperature
range, otherwise specifications are at T
A
= 25°C. V
IN
= 3V, C
L
= 1µF unless otherwise specified.
CONDITIONS
LT1790ACS6-2.5
LT1790BCS6-2.5
Output Voltage Temperature Coefficient (Note 5)
Line Regulation
Load Regulation (Note 6)
LT1790ACS6-2.5
LT1790BCS6-2.5
3V
≤
V
IN
≤
18V
q
q
q
MIN
2.49875
–0.05
2.4975
–0.1
TYP
2.50
2.50
5
12
50
80
MAX
2.50125
0.05
2.5025
0.1
10
25
170
220
160
250
110
100
400
250
60
75
125
UNITS
V
%
V
%
ppm/°C
ppm/°C
ppm/V
ppm/V
ppm/mA
ppm/mA
ppm/mA
mV
mV
mV
µA
µA
µA
µs
µV
P-P
µV
RMS
ppm/√kHr
ppm
ppm
I
OUT
Source = 5mA
I
OUT
Source = 5mA
I
OUT
Sink = 5mA
V
IN
– V
OUT
,
∆V
OUT
≤
0.1%
I
OUT
= 0mA
I
OUT
Source = 5mA
I
OUT
Sink = 5mA
V
OUT
= 2.5V
q
70
q
q
Dropout Voltage (Note 7)
60
300
40
35
Supply Current
Minimum Current
Turn-On Time
Output Noise (Note 8)
Long-Term Drift of Output Voltage (Note 9)
Hysteresis (Note 10)
q
V
OUT
= – 2.5V
C
LOAD
= 1µF
0.1Hz
≤
f
≤
10Hz
10Hz
≤
f
≤
1kHz
∆T
= 0°C to 70°C
∆T
= – 40°C to 85°C
q
q
100
700
12
33
50
40
60
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
The LT1790S6 is guaranteed functional over the operating
temperature range of – 40°C to 125°C.
Note 3:
If the part is stored outside of the specified temperature range, the
output voltage may shift due to hysteresis.
Note 4:
ESD (Electrostatic Discharge) sensitive device. Extensive use of
ESD protection devices are used internal to the LT1790, however, high
electrostatic discharge can damage or degrade the device. Use proper ESD
handling precautions.
2
U
W
U
U
W W
W
LT1790-2.5
ELECTRICAL CHARACTERISTICS
Note 5:
Temperature coefficient is measured by dividing the change in
output voltage by the specified temperature range. Incremental slope is
also measured at 25°C.
Note 6:
Load regulation is measured on a pulse basis from no load to the
specified load current. Output changes due to die temperature change
must be taken into account separately.
Note 7:
Excludes load regulation errors.
Note 8:
Peak-to-peak noise is measured with a single pole highpass filter
at 0.1Hz and a 2-pole lowpass filter at 10Hz. The unit is enclosed in a still
air environment to eliminate thermocouple effects on the leads. The test
time is 10 seconds. RMS noise is measured with a single pole highpass
filter at 10Hz and a 2-pole lowpass filter at 1kHz. The resulting output is
full-wave rectified and then integrated for a fixed period, making the final
reading an average as opposed to RMS. A correction factor of 1.1 is used
to convert from average to RMS and a second correction of 0.88 is used to
correct for the nonideal bandpass of the filters.
Note 9:
Long-term drift typically has a logarithmic characteristic and
therefore changes after 1000 hours tend to be smaller than before that
time. Total drift in the second thousand hours is normally less than one
third that to the first thousand hours with a continuing trend toward
reduced drift with time. Long-term drift is affected by differential stress
between the IC and the board material created during board assembly. See
Applications Information.
Note 10:
Hysteresis in the output voltage is created by package stress that
differs depending on whether the IC was previously at a higher or lower
temperature. Output voltage is always measured at 25°C, but the IC is
cycled to 85°C or – 40°C before a successive measurements. Hysteresis is
roughly proportional to the square of the temperature change. Hysteresis
is not normally a problem for operational temperature excursions where
the instrument might be stored at high or low temperature. See
Applications Information.
TYPICAL PERFOR A CE CHARACTERISTICS
Output Voltage Temperature Drift
2.508
2.506
2.504
2.502
2.500
2.498
2.496
2.494
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
1790 G13
FOUR TYPICAL PARTS
T
A
= –55°C
T
A
= 125°C
T
A
= 25°C
VOLTAGE DIFFERENTIAL (mV)
OUTPUT CURRENT (mA)
OUTPUT VOLTAGE (V)
Load Regulation (Sourcing)
0
OUTPUT VOLTAGE CHANGE (mV)
T
A
= 25°C
T
A
= –55°C
OUTPUT VOLTAGE CHANGE (mV)
5
–1
–2
T
A
= 125°C
SUPPLY CURRENT (µA)
–3
–4
–5
0.1
1
OUTPUT CURRENT (mA)
U W
10
1790 616
Minimum Input-Output Voltage
Differential (Sourcing) Series Mode
10
Minimum Input-Output Voltage
Differential (Sinking) Series Mode
90
70
50
30
10
–10
–30
–50 –30 –10 10 30 50 70 90 110 130
TEMPERATURE (°C)
1790 G15
1
100µA
1mA
5mA
0.1
0
0.1
0.2
0.3
0.4
0.5
INPUT-OUTPUT VOLTAGE (V)
0.6
1790 G14
Load Regulation (Sinking)
80
70
Supply Current vs Input Voltage
4
60
50
T
A
= –55°C
3
T
A
= –55°C
2
T
A
= 125°C
1
T
A
= 25°C
0
0.1
1
OUTPUT CURRENT (mA)
10
1790 617
T
A
= 25°C
40
30
T
A
= 125°C
20
10
0
0
5
10
INPUT VOLTAGE (V)
1790 G18
15
20
3
LT1790-2.5
TYPICAL PERFOR A CE CHARACTERISTICS
Line Regulation
2.515
T
A
= 125°C
2.510
OUTPUT VOLTAGE (V)
POWER SUPPLY REJECTION RATIO (dB)
OUTPUT IMPEDANCE (Ω)
2.505
T
A
= 25°C
2.500
2.495
2.490
2.489
0
2
4
6 8 10 12 14 16 18 20
INPUT VOLTAGE (V)
1790 G19
T
A
= –55°C
– 2.5V Characteristics
0.30
R1 10k
4
3V
6
V
OUT
1µF
0.25
CURRENT IN R
L
(mA)
0.20
0.15
0.10
0.05
–V
EE
ppm
0
–4.0 –3.5 –3.0 –2.5 –2.0 –1.5 –1.0 –0.5
OUTPUT TO GROUND VOLTAGE (V)
Output Noise 0.1Hz to 10Hz
10
OUTPUT NOISE (5µV/DIV)
NOISE VOLTAGE (µV/√Hz)
0
1
2
4
U W
3
Power Supply Rejection Ratio
vs Frequency
20
10
0
–10
–20
–30
–40
–50
–60
–70
–80
100
1k
10k
100k
FREQUENCY (Hz)
1M
1790 G20
Output Impedance vs Frequency
1000
C
L
= 1µF
C
L
= 0.47µF
C
L
= 1µF
100
C
L
= 4.7µF
10
1
100
1k
10k
FREQUENCY (Hz)
100k
1790 G21
Long-Term Drift
(Data Points Reduced After 500 Hr)
140
T
A
= 30°C
120 2 TYPICAL PARTS SOLDERED TO PCB
100
80
60
40
20
0
LT1790-2.5
1, 2
R
L
5k
T
A
= 25°C
T
A
= 125°C
T
A
= –55°C
0
–20
–40
–60
0
200
600
400
HOURS
800
1000
1790 G23
1790 G22
Output Voltage Noise Spectrum
C
L
= 1µF
8
6
I
O
= 0µA
I
O
= 100µA
I
O
= 250µA
4
2
I
O
= 1mA
0
4 5 6
TIME (SEC)
7
8
9
10
10
100
1k
FREQUENCY (Hz)
10k
1790 G25
1790 G24
LT1790-2.5
APPLICATIONS INFORMATION
Bypass and Load Capacitors
The LT1790-2.5 voltage reference should have an input
bypass capacitor of 0.1µF or larger, however the bypass-
ing of other local devices may serve as the required
component. This reference also requires an output capaci-
tor for stability. The optimum output capacitance for most
applications is 1µF, although larger values work as well.
This capacitor affects the turn-on and settling time for the
output to reach its final value.
Figure 1 shows the turn-on time for the LT1790-2.5 with
a 1µF input bypass and 1µF load capacitor. Figure 2 shows
the output response to a 0.5V transient on V
IN
with the
same capacitors.
V
GEN
3V
2V
3V
2V
1V
0V
1790 F01
Figure 1. Turn-On Characteristics of LT1790-2.5
3V
2V
1V
0V
1790 F02
Figure 2. Output Response to 0.5V Ripple on V
IN
U
V
IN
V
IN
W
U
U
The test circuit of Figure 3 is used to measure the stability
of various load currents. With R
L
= 1k, the 1V step
produces a current step of 1mA. Figure 4 shows the
response to a
±0.5mA
load. Figure 5 is the output re-
sponse to a sourcing step from 4mA to 5mA, and Figure
6 is the output response of a sinking step from – 4mA to
– 5mA.
V
IN
3V
4
C
IN
0.1µF
6
C
L
1µF
1k
V
GEN
1V
1790 F03
LT1790-2.5
1, 2
Figure 3. Response Time Test Circuit
V
OUT
V
OUT
1790 F04
Figure 4. LT1790-2.5 Sourcing and Sinking 0.5mA
V
OUT
V
OUT
V
GEN
–2V
–3V
1790 F05
Figure 5. LT1790-2.5 Sourcing 4mA to 5mA
5
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