LTC1798 Series
1
1798fc
TYPICAL APPLICATION
DESCRIPTION
Micropower Low
Dropout References
The LTC
®
1798/LTC1798-2.5/LTC1798-3/LTC1798-4.1/
LTC1798-5 are micropower bandgap references that
combine high accuracy and low drift with very low supply
current and small package size. The combination of ultralow
quiescent current and low dropout voltage of only 200mV
(max) makes them ideal for battery-powered equipment.
The output voltage is set by an external resistor divider
for the adjustable LTC1798.
This series of references uses curvature compensation to
obtain low temperature coefficient and trimmed thin-film
resistors to achieve high output accuracy. These references
can source up to 10mA and sink up to 2mA, making them
ideal for precision regulator applications. They are stable
without an output bypass capacitor, but are also stable
with capacitance up to 1µF. This feature is important in
critical applications where PC board space is a premium
and fast settling is demanded.
The LTC1798 series references provided power dissipation
advantages over shunt references. In addition to supply
current, shunt references must also idle the entire load
current to operate.
The LTC1798 series is available in the SO-8 package.
2.5V Battery-Powered Reference
FEATURES
APPLICATIONS
n 200mV Max Dropout at 10mA Output Current
n 4µA Typical Quiescent Current
n 0.15% Max Initial Accuracy
n No Output Capacitor Required
n Output Sources 10mA, Sinks 2mA
n 40ppm/°C Max Drift
n Voltage Options: 2.5V, 3V, 4.1V, 5V and Adjustable
n Battery-Powered Systems
n Handheld Instruments
n Precision Power Supplies
n A/D and D/A Converters
n Available in the SO-8 Package
LTC1798-2.5 Temperature Drift
LTC1798-2.5
OUT
IN
GND
4
2
2.7V
TO 12.6V
62.5V
1798 TA01
0.1µF
TEMPERATURE (°C)
–40 –20 0 20 40 60 80 100
REFERENCE VOLTAGE CHANGE (mV)
1798 TA02
4
3
2
1
–2
–1
–3
–4
0
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
LTC1798 Series
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PIN CONFIGURATIONABSOLUTE MAXIMUM RATINGS
Operating Temperature Range...................... 0°C to 70°C
Extended Commercial Operating
Temperature Range .................................. –40°C to 85°C
Junction Temperature ........................................... 110°C
Storage Temperature Range ................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
(Note 1)
1
2
3
4
8
7
6
5
TOP VIEW
DNC*
DNC*
OUT
DNC*
*DNC
IN
**DNC/FB
GND
S8 PACKAGE
8-LEAD PLASTIC SO
TJMAX = 125°C, qJA = 190°C/W
* CONNECTED INTERNALLY. DO NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS
** DNC FOR LTC1798-2.5/LTC1798-3/LTC1798-4.1/LTC1798-5, FB FOR LTC1798
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION SPECIFIED TEMPERATURE RANGE
LTC1798CS8#PBF (OBSOLETE) LTC1798CS8#TRPBF 1798 8-Lead Plastic SO 0°C to 70°C
LTC1798CS8-2.5#PBF LTC1798CS8-2.5#TRPBF 179825 8-Lead Plastic SO 0°C to 70°C
LTC1798CS8-3#PBF LTC1798CS8-3#TRPBF 17983 8-Lead Plastic SO 0°C to 70°C
LTC1798CS8-4.1#PBF LTC1798CS8-4.1#TRPBF 179841 8-Lead Plastic SO 0°C to 70°C
LTC1798CS8-5#PBF LTC1798CS8-5#TRPBF 17985 8-Lead Plastic SO 0°C to 70°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
AVAILABLE OPTIONS
OUTPUT VOLTAGE
(V)
TEMPERATURE
RANGE
(ºC)
ACCURACY
(%)
TEMPERATURE
COEFFICIENT
(PPM/ºC)
PACKAGE STYLE
SO-8 (S8)
ORDER NUMBER PART MARKING
2.5 0 to 70 0.15 40 LTC1798CS8-2.5 179825
3 0 to 70 0.15 40 LTC1798CS8-3 17983
4.096 0 to 70 0.15 40 LTC1798CS8-4.1 179841
5 0 to 70 0.15 40 LTC1798CS8-5 17985
Adjustable 0 to 70 0.4 40 LTC1798CS8 1798
LTC1798 Series
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ELECTRICAL CHARACTERISTICS
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LTC1798 is guaranteed functional over the operating
temperature range of –40°C to 100°C.
Note 3: If the part is stored outside of the specified operating temperature
range, the output may shift due to hysteresis.
Note 4: ESD (Electostatic Discharge) sensitive device. Extensive use of
ESD protection devices are used internal to the LTC1798, however, high
electrostatic discharge can damage or degrade the device. Use proper ESD
handling precautions.
Note 5: Peak-to-peak noise is measured with a single pole highpass filter
at 0.1Hz and 2-pole lowpass filter at 10Hz.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
VIN Input Voltage Range l12.6 V
IIN Input Current FB = OUT for LTC1798
l
4 6.5
8.5
µA
µA
VOUT Output Voltage (Note 4) LTC1798, FB = OUT
LTC1798 ADJ
LTC1798-2.5
LTC1798-3
LTC1798-4.1
LTC1798-5
LTC1798 All Fixed Options
2.3755
–0.4
2.4963
2.9955
4.090
4.9925
–0.15
2.385
2.5
3
4.096
5
2.3945
0.4
2.5037
3.0045
4.102
5.0075
0.15
V
%
V
V
V
V
%
enOutput Voltage Noise (Note 5) 0.1Hz ≤ f ≤ 10Hz 8 ppmP-P
TC Output Voltage Temp Coefficient (Note 6) TMIN ≤ TJ ≤ TMAX l15 40 ppm/°C
VOUT/VIN Line Regulation VIN = (VOUT(NOMINAL) + 0.2V) to 12.6V l30 120 ppm/V
VOUT/IOUT Load Regulation (Note 7) Sourcing 0mA to 10mA l0.1 0.3 mV/mA
Sinking 0mA to 2mA
l
1.75 4
6.5
mV/mA
mV/mA
ISC Short-Circuit Output Current VOUT Shorted to GND
VOUT Shorted to VIN
20
2
40
4
mA
mA
VDO Dropout Voltage (Note 8) IOUT = 0, VOUT ≤ 0.1%
IOUT = 10mA, VOUT ≤ 0.1%
l
l
100
200
mV
mV
VHYST Output Hysteresis (Note 9) T = –40°C to 85°C
T = 0°C to 70°C
200
50
ppm
ppm
IFB FB Pin Input Current LTC1798, OUT = FB 10 nA
The l denotes specifications which apply over the full specified temperature
range, otherwise specifications are at TA = 25°C. VIN = VOUT(NOMINAL) + 0.2V, IOUT = 0mA unless otherwise noted. FB = OUT for the LTC1798.
Note 6: Temperature coefficient is the change in output voltage divided by
the nominal output voltage divided by the specified temperature range.
Note 7: 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 8: Dropout voltage is (VIN – VOUT) when VOUT falls to 0.1% below its
nominal value at VIN = VOUT + 0.5V.
Note 9: Hysteresis in 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 hot or cold before successive measurements. Hysteresis is not
normally a problem for operational temperature excursions where the
instrument might be stored at high or low temperature.
LTC1798 Series
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TYPICAL PERFORMANCE CHARACTERISTICS
OUTPUT SOURCE CURRENT (mA)
DROPOUT VOLTAGE (mV)
100
90
80
70
60
50
40
30
20
10
00 1 10 100
1798 G01
0.1
TA = 25°C
TEMPERATURE (°C)
–50 –25
INPUT CURRENT (µA)
150
1798 G02
0 25 50 75 100 125
8
7
6
5
4
3
2
1
0
VIN = 2.7V
TEMPERATURE (°C)
–50 –25
OUTPUT SHORT-CIRCUIT CURRENT (mA)
150
1798 G03
0 25 50 75 100 125
70
60
50
40
30
20
10
5
0
TA = 25°C
VIN = VOUT(NOM) + 0.2V
OUTPUT
SHORTED
TO VIN
OUTPUT
SHORTED
TO GND
INPUT VOLTAGE (V)
2
OUTPUT SHORT-CIRCUIT CURRENT (mA)
25
20
15
10
5
0
46 8 10
1798 G04
12 14
TA = 25°C
OUTPUT SHORTED
TO VIN
INPUT VOLTAGE (V)
2
OUTPUT SHORT-CIRCUIT CURRENT (mA)
42
41
46 8 10
1798 G05
12 14
TA = 25°C
OUTPUT SHORTED
TO GND
OUTPUT CURRENT (mA)
VOUT FROM NO LOAD (mV)
5
4
3
2
1
0
–1
–2
–3
–4
–5 0 1 10 100
1798 G06
0.1
TA = 25°C
VIN = VOUT(NOM) + 0.2V
SINKING
SOURCING
INPUT VOLTAGE (V)
2
OUTPUT VOLTAGE (V)
2.5010
2.5005
2.5000
2.4995 46 8 10
1798 G07
12 14
TA = 25°C
INPUT VOLTAGE (V)
2
INPUT CURRENT (µA)
7
6
5
446 8 10
1798 G08
12 14
TA = 25°C
FREQUENCY (Hz)
POWER SUPPLY REJECTION RATIO (dB)
60
50
40
30
20
10
010 1k 10k
1798 G09
100
VIN = 2.7V
LTC1798-2.5* Output Short-Circuit
Current vs Input Voltage
LTC1798-2.5* Output Short-Circuit
Current vs Input Voltage
LTC1798 Series
Load Regulation
LTC1798-2.5*
Output Voltage vs Input Voltage
LTC1798-2.5*
Input Current vs Input Voltage
LTC1798-2.5
PSRR vs Frequency
LTC1798-2.5* Dropout Voltage
vs Output Source Current
LTC1798-2.5*
Input Current vs Temperature
LTC1798 Series Output Short-Circuit
Current vs Temperature
LTC1798 Series
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TYPICAL PERFORMANCE CHARACTERISTICS
5µV/DIV
1798 G10
1SEC/DIV
VIN = 2.7V
INPUT VOLTAGE (V)
012345678910
INPUT CURRENT (µA)
1798 G11
1400
1200
1000
800
600
400
200
0
TA = –55°C
TA = 25°C
TA = 125°C
INPUT VOLTAGE (V)
00.5 1 1.5 2 2.5 3 3.5 4 4.5 5
INPUT CURRENT (µA)
1798 G12
250
200
150
100
50
0
TA = 25°C
TA = –55°C
TA = 125°C
LTC1798-2.5
0.1Hz to 10Hz Noise
LTC1798-5 Input Current
vs Input Voltage in Dropout
LTC1798-2.5 Input Current
vs Input Voltage in Dropout
PIN FUNCTIONS
DNC (Pins 1, 5, 7, 8): Do Not Connect. Connected
internally for post package trim. These pins must be left
unconnected.
IN (Pin 2): Positive Supply. Bypassing with a 0.1µF capaci-
tor is recommended if the output loading changes. (VOUT
+ 0.2V) ≤ VIN ≤ 12.6V.
DNC (Pin 3): (LTC1798-2.5/LTC1798-3/LTC1798-4.1/
LTC1798-5) Do Not Connect. Connected internally for post
package trim. This pin must be left unconnected.
FB (Pin 3): (LTC1798) Resistor Divider Feedback Pin.
Connect a resistor divider from OUT to GND and the center
tap to FB. This pin sets the output potential.
VV
RR
R
OUT =+
2 385
12
2
.;
R1 is connected from OUT
to FB and R2 from FB to GND. Selecting R2 ≥ 10k will
make IOUT < 250µA.
GND (Pin 4): Negative Supply or Ground Connection.
OUT (Pin 6): Reference Output. The output can source
up to 10mA and sink up to 2mA. It is stable with output
bypass capacitor ranging from 0µF to 1µF.
LTC1798 Series
6
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Figure 1. Reference Output Load Transient Response, 1µF Output Capacitor
10ms/DIV
VOUT
100mV/DIV
IOUT
1mA
0mA
1798 F01a
Longer Battery Life
Series references have an advantage over shunt style
references. To operate, shunt references require a resistor
between the power supply and the output. This resistor
must be chosen to supply the maximum current that is
demanded by the circuit being regulated. When the circuit
being controlled is not operating at this maximum current,
the shunt reference must always sink this current, resulting
in high power dissipation and short battery life.
The LTC1798 series low dropout references do not require
a current setting resistor and can operate with any supply
voltage from (VOUT(NOMINAL) + 0.2V) to 12.6V. When the
circuitry being regulated does not demand current, the
LTC1798 series reduces its dissipation and battery life is
extended. If the reference is not delivering load current it
BLOCK DIAGRAM
+
IN
6
1798 BD
2
4
OUT
3 (LTC1798)FB
2.385V
GND
R1
R2
NOTE: R1 AND R2 ARE NOT CONNECTED FOR LTC1798
0.5ms/DIV
VOUT
100mV/DIV
IOUT
1mA
0mA
1798 F01b
APPLICATIONS INFORMATION
dissipates only 10.8µW when operating on a 2.7V supply
for LTC1798-2.5, yet the same connection can deliver
10mA of load current when demanded.
Output Bypass Capacitor
The LTC1798 series is designed to be stable with or without
capacitive loads. With no capacitive load, the reference
is ideal for fast settling applications, or where PC board
space is at a premium.
In applications with significant output loading changes, an
output bypass capacitor of up to 1µF can be used to improve
the output transient response. Figure 1 shows the response
of the reference to a 1mA to 0µA load step with a 1µF output
capacitor. If more than 1µF of output capacitance is required,
a resistor in series with the capacitor is recommended
LTC1798 Series
7
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LTC1798-5
OUT
IN
GND
4
2
5.2V
TO
12.6V
65V
1798 F02
0.1µF
COUT
>1µF
DAMPING RESISTOR
<1k
APPLICATIONS INFORMATION
Figure 2. Adding a Damping Resistor with
Output Capacitors Greater Than 1µF
Figure 3. Damping Resistance vs Output Capacitor Value
OUTPUT CAPACITOR VALUE (µF)
1
10
RESISTOR VALUE (Ω)
100
1k
10k
10 100 1000
1798 F03
These references consume only 4µA of quiescent current
under light and heavy loads as well as in dropout; whereas,
PNP-based references waste considerable amounts of cur-
rent when the pass transistor is saturated. In addition, the
LTC1798 series provides a lower dropout voltage (200mV
max) than PNP-based references.
to reduce the output ringing. Figure 2 illustrates the use of
a damping resistor for capacitive loads greater than 1µF.
Figure 3 shows the resistor and capacitor values required
to achieve critical damping.
Internal P-Channel Pass Transistor
The LTC1798 series features an internal P-channel MOSFET
pass transistor. This provides several advantages over
similar designs using a PNP bipolar pass transistor.
LTC1798 Series
8
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PACKAGE DESCRIPTION
Dimensions in inches (millimeters) unless otherwise noted.
S8 Package
8-Lead Plastic Small Outline (Narrow .150 Inch)
(Reference LTC DWG # 05-08-1610)
.016 – .050
(0.406 – 1.270)
.010 – .020
(0.254 – 0.508)¥ 45
0– 8 TYP
.008 – .010
(0.203 – 0.254)
SO8 0303
.053 – .069
(1.346 – 1.752)
.014 – .019
(0.355 – 0.483)
TYP
.004 – .010
(0.101 – 0.254)
.050
(1.270)
BSC
1234
.150 – .157
(3.810 – 3.988)
NOTE 3
8765
.189 – .197
(4.801 – 5.004)
NOTE 3
.228 – .244
(5.791 – 6.197)
.245
MIN .160 .005
RECOMMENDED SOLDER PAD LAYOUT
.045 .005
.050 BSC
.030 .005
TYP
INCHES
(MILLIMETERS)
NOTE:
1. DIMENSIONS IN
2. DRAWING NOT TO SCALE
3. THESE DIMENSIONS DO NOT INCLUDE MOLD FLASH OR PROTRUSIONS.
MOLD FLASH OR PROTRUSIONS SHALL NOT EXCEED .006" (0.15mm)
LTC1798 Series
9
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REVISION HISTORY
REV DATE DESCRIPTION PAGE NUMBER
C 9/10 Added Maximum limit for VIN in Electrical Characteristics section 3
(Revision history begins at Rev C)
LTC1798 Series
10
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 FAX: (408) 434-0507 www.linear.com
LINEAR TECHNOLOGY CORPORATION 2008
LT 0910 REV C • PRINTED IN USA
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+
1
4
8
VSS = –4V
VOUT = –3V
0.2V ≤ VCC ≤ 8.5V
3
2
LTC1798-3
1/2 LTC1542
OUT
GND
4
6
1798 TA03
IN
2
0.1µF
Micropower Low Dropout Negative Reference
LTC1798-2.5
OUT
IN
GND
4
2
VCC = 5V 62.5V
VIRTUAL
GROUND
1798 TA04
0.1µF 0.1µF
Supply Splitter
LTC1798-3
LTC1096L
MPU
SERIAL DATA LINK
(MICROWIRE AND
SPI COMPATIBLE)
OUT
IN
GND
CS/
SHDN
+IN
–IN
GND
VCC
CLK
DOUT
VREF
ANALOG INPUT
0V TO 3V RANGE
1
2
3
4
8
7
6
5
42VIN
3.2V TO
12.6V
6
1798 TA05
1µF
SERIAL DATA LINK
0.1µF
Low Power, Low Voltage Supply Reference for LTC1096L