Datasheet LT1761ES5-2.5, LT1761ES5-2, LT1761ES5-1.8, LT1761ES5-5, LT1761ES5-3.3 Datasheet (Linear Technology)
...Page 1
FEATURES
■
Tiny 5-Lead SOT-23 Package
■
Low Noise: 20µV
■
Low Quiescent Current: 20µA
■
Wide Input Voltage Range: 1.8V to 20V
■
Output Current: 100mA
■
Very Low Shutdown Current: < 0.1µA
■
Low Dropout Voltage: 300mV at 100mA
■
Fixed Output Voltages: 1.5V, 1.8V, 2V, 2.5V, 2.8V,
(10Hz to 100kHz)
RMS
3V, 3.3V, 5V
■
Adjustable Output from 1.22V to 20V
■
Stable with 1µF Output Capacitor
■
Stable with Aluminum, Tantalum or
Ceramic Capacitors
■
Reverse Battery Protected
■
No Reverse Current
■
No Protection Diodes Needed
■
Overcurrent and Overtemperature Protected
U
APPLICATIO S
■
Cellular Phones
■
Pagers
■
Battery-Powered Systems
■
Frequency Synthesizers
■
Wireless Modems
LT1761 Series
100mA, Low Noise,
LDO Micropower
Regulators in SOT-23
U
DESCRIPTIO
The LT®1761 series are micropower, low noise, low
dropout regulators. With an external 0.01µF bypass
capacitor, output noise drops to 20µV
100kHz bandwidth. Designed for use in battery-powered
systems, the low 20µA quiescent current makes them an
ideal choice. In shutdown, quiescent current drops to less
than 0.1µA. The devices are capable of operating over an
input voltage from 1.8V to 20V, and can supply 100mA of
output current with a dropout voltage of 300mV. Quiescent current is well controlled, not rising in dropout as it
does with many other regulators.
The LT1761 regulators are stable with output capacitors
as low as 1µF. Small ceramic capacitors can be used
without the series resistance required by other regulators.
Internal protection circuitry includes reverse battery protection, current limiting, thermal limiting and reverse
current protection. The device is available in fixed output
voltages of 1.5V, 1.8V, 2V, 2.5V, 2.8V, 3V, 3.3V and 5V,
and as an adjustable device with a 1.22V reference voltage.
The LT1761 regulators are available in the 5-lead SOT-23
package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
over a 10Hz to
RMS
TYPICAL APPLICATIO
5V Low Noise Regulator
V
5.4V TO
20V
IN
1µF
IN
SHDN
OUT
LT1761-5
BYP
GND
U
0.01µF
+
5V AT100mA
20µV
10µF
RMS
NOISE
1761 TA01
V
OUT
100µV/DIV
10Hz to 100kHz Output Noise
1761 G48
20µV
RMS
1
Page 2
LT1761 Series
WWWU
ABSOLUTE AXI U RATI GS
(Note 1)
IN Pin Voltage........................................................ ±20V
OUT Pin Voltage .................................................... ±20V
Input to Output Differential Voltage ....................... ±20V
ADJ Pin Voltage ...................................................... ±7V
BYP Pin Voltage....................................................±0.6V
SHDN Pin Voltage................................................. ±20V
UU
W
PACKAGE/ORDER I FOR ATIO
TOP VIEW
TOP VIEW
5 OUT
IN 1
IN 1
GND 2
GND 2
BYP 3
BYP 3
S5 PACKAGE
S5 PACKAGE
5-LEAD PLASTIC SOT-23
5-LEAD PLASTIC SOT-23
T
= 150°C, θJA = 250°C/W
JMAX
SEE THE APPLICATIONS INFORMATION SECTION.
ORDER PART
NUMBER
LT1761ES5-BYP
5 OUT
4 ADJ
4 ADJ
S5 PART
MARKING
LTGC LTGH LT1761ES5-1.5
LT1761ES5-SD
IN 1
GND 2
SHDN 3
S5 PACKAGE
5-LEAD PLASTIC SOT-23
T
= 150°C, θJA = 250°C/W
JMAX
SEE THE APPLICATIONS INFORMATION SECTION.
ORDER PART
NUMBER
Output Short-Circut Duration.......................... Indefinite
Operating Junction Temperature Range
(Note 2) ............................................ –40°C to 125°C
Storage Temperature Range ................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
TOP VIEW
5 OUT
4 ADJ
S5 PART
MARKING
GND 2
SHDN 3
SEE THE APPLICATIONS INFORMATION SECTION.
ORDER PART
NUMBER
TOP VIEW
IN 1
S5 PACKAGE
5-LEAD PLASTIC SOT-23
T
= 150°C, θJA = 250°C/W
JMAX
5 OUT
4 BYP
S5 PART
MARKING
LT1761ES5-1.8
LT1761ES5-2
LT1761ES5-2.5
LT1761ES5-2.8
LT1761ES5-3
LT1761ES5-3.3
LT1761ES5-5
LTMT
LTJM
LTJE
LTGD
LTLB
LTGE
LTGF
LTGG
Consult factory for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. (Note 2)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Minimum Input Voltage (Notes 3, 11) I
Regulated Output Voltage LT1761-1.5 VIN = 2V, I
(Note 4) 2.5V < V
= 100mA ● 1.8 2.3 V
LOAD
= 1mA 1.478 1.5 1.522 V
LOAD
IN
2.5V < V
IN
LT1761-1.8 VIN = 2.3V, I
LT1761-2 VIN = 2.5V, I
LT1761-2.5 VIN = 3V, I
2.8V < V
IN
2.8V < V
IN
< 20V, 1mA < I
3V < V
IN
3V < VIN < 20V, 1mA < I
3.5V < V
IN
3.5V < VIN < 20V, 1mA < I
< 20V, 1mA < I
< 20V, 1mA < I
= 1mA 1.775 1.8 1.825 V
LOAD
< 20V, 1mA < I
< 20V, 1mA < I
= 1mA 1.970 2 2.030 V
LOAD
= 1mA 2.465 2.5 2.535 V
LOAD
< 20V, 1mA < I
< 50mA ● 1.457 1.5 1.538 V
LOAD
< 100mA ● 1.436 1.5 1.555 V
LOAD
< 50mA ● 1.750 1.8 1.845 V
LOAD
< 100mA ● 1.725 1.8 1.860 V
LOAD
< 50mA ● 1.945 2 2.045 V
LOAD
< 100mA ● 1.920 2 2.060 V
LOAD
< 50mA ● 2.435 2.5 2.565 V
LOAD
< 100mA ● 2.415 2.5 2.575 V
LOAD
2
Page 3
LT1761 Series
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. (Note 2)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Regulated Output Voltage LT1761-2.8 VIN = 3.3V, I
(Note 4) 3.8V < V
3.8V < V
LT1761-3 VIN = 3.5V, I
4V < V
IN
4V < VIN < 20V, 1mA < I
LT1761-3.3 VIN = 3.8V, I
4.3V < V
4.3V < V
LT1761-5 VIN = 5.5V, I
6V < V
IN
6V < V
IN
ADJ Pin Voltage LT1761 VIN = 2V, I
(Note 3, 4) 2.3V < V
2.3V < V
Line Regulation LT1761-1.5 ∆VIN = 2V to 20V, I
LT1761-1.8 ∆V
LT1761-2 ∆V
LT1761-2.5 ∆V
LT1761-2.8 ∆V
LT1761-3 ∆V
LT1761-3.3 ∆V
LT1761-5 ∆V
LT1761(Note 3) ∆V
= 2.3V to 20V, I
IN
= 2.5V to 20V, I
IN
= 3V to 20V, I
IN
= 3.3V to 20V, I
IN
= 3.5V to 20V, I
IN
= 3.8V to 20V, I
IN
= 5.5V to 20V, I
IN
= 2V to 20V, I
IN
Load Regulation LT1761-1.5 VIN = 2.5V, ∆I
V
= 2.5V, ∆I
IN
= 2.5V, ∆I
V
IN
= 2.5V, ∆I
V
IN
LT1761-1.8 VIN = 2.8V, ∆I
V
= 2.8V, ∆I
IN
= 2.8V, ∆I
V
IN
= 2.8V, ∆I
V
IN
LT1761-2 VIN = 3V, ∆I
= 3V, ∆I
V
IN
V
= 3V, ∆I
IN
= 3V, ∆I
V
IN
LT1761-2.5 VIN = 3.5V, ∆I
= 3.5V, ∆I
V
IN
V
= 3.5V, ∆I
IN
= 3.5V, ∆I
V
IN
LT1761-2.8 VIN = 3.8V, ∆I
= 3.8V, ∆I
V
IN
V
= 3.8V, ∆I
IN
= 3.8V, ∆I
V
IN
LT1761-3 VIN = 4V, ∆I
= 4V, ∆I
V
IN
V
= 4V, ∆I
IN
= 4V, ∆I
V
IN
= 1mA 2.762 2.8 2.838 V
LOAD
< 20V, 1mA < I
IN
< 20V, 1mA < I
IN
= 1mA 2.960 3 3.040 V
LOAD
< 20V, 1mA < I
= 1mA 3.250 3.3 3.350 V
LOAD
< 20V, 1mA < I
IN
< 20V, 1mA < I
IN
= 1mA 4.935 5 5.065 V
LOAD
< 20V, 1mA < I
< 20V, 1mA < I
= 1mA 1.205 1.220 1.235 V
LOAD
< 20V, 1mA < I
IN
< 20V, 1mA < I
IN
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
LOAD
= 1mA to 50mA 10 20 mV
LOAD
= 1mA to 50mA ● 35 mV
LOAD
= 1mA to 100mA 14 30 mV
LOAD
= 1mA to 100mA ● 55 mV
LOAD
= 1mA to 50mA 10 20 mV
LOAD
= 1mA to 50mA ● 35 mV
LOAD
= 1mA to 100mA 15 30 mV
LOAD
= 1mA to 100mA ● 60 mV
LOAD
= 1mA to 50mA 10 20 mV
LOAD
= 1mA to 50mA ● 35 mV
LOAD
= 1mA to 100mA 15 35 mV
LOAD
= 1mA to 100mA ● 65 mV
LOAD
= 1mA to 50mA 10 20 mV
LOAD
= 1mA to 50mA ● 35 mV
LOAD
= 1mA to 100mA 20 40 mV
LOAD
= 1mA to 100mA ● 80 mV
LOAD
= 1mA to 50mA 10 20 mV
LOAD
= 1mA to 50mA ● 38 mV
LOAD
= 1mA to 100mA 20 40 mV
LOAD
= 1mA to 100mA ● 86 mV
LOAD
= 1mA to 50mA 10 20 mV
LOAD
= 1mA to 50mA ● 40 mV
LOAD
= 1mA to 100mA 20 40 mV
LOAD
= 1mA to 100mA ● 90 mV
LOAD
< 50mA ● 2.732 2.8 2.868 V
LOAD
< 100mA ● 2.706 2.8 2.884 V
LOAD
< 50mA ● 2.930 3 3.070 V
LOAD
< 100mA ● 2.900 3 3.090 V
LOAD
< 50mA ● 3.230 3.3 3.370 V
LOAD
< 100mA ● 3.190 3.3 3.400 V
LOAD
< 50mA ● 4.900 5 5.100 V
LOAD
< 100mA ● 4.850 5 5.120 V
LOAD
< 50mA ● 1.190 1.220 1.250 V
LOAD
< 100mA ● 1.170 1.220 1.260 V
LOAD
= 1mA ● 110 mV
= 1mA ● 110 mV
= 1mA ● 110 mV
= 1mA ● 110 mV
= 1mA ● 110 mV
= 1mA ● 110 mV
= 1mA ● 110 mV
= 1mA ● 110 mV
= 1mA ● 110 mV
3
Page 4
LT1761 Series
ELECTRICAL CHARACTERISTICS
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C. (Note 2)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Load Regulation LT1761-3.3 VIN = 4.3V, ∆I
VIN = 4.3V, ∆I
V
= 4.3V, ∆I
IN
VIN = 4.3V, ∆I
LT1761-5 VIN = 6V, ∆I
V
= 6V, ∆I
IN
VIN = 6V, ∆I
V
= 6V, ∆I
IN
LT1761 (Note 3) VIN = 2.3V, ∆I
V
= 2.3V, ∆I
IN
VIN = 2.3V, ∆I
V
= 2.3V, ∆I
IN
Dropout Voltage I
VIN = V
OUT(NOMINAL)
(Notes 5, 6, 11) I
GND Pin Current I
V
= V
IN
OUT(NOMINAL)
(Notes 5, 7) I
Output Voltage Noise C
= 1mA 0.10 0.15 V
LOAD
I
= 1mA ● 0.19 V
LOAD
= 10mA 0.17 0.22 V
LOAD
I
= 10mA ● 0.29 V
LOAD
I
= 50mA 0.24 0.28 V
LOAD
I
= 50mA ● 0.38 V
LOAD
I
= 100mA 0.30 0.35 V
LOAD
I
= 100mA ● 0.45 V
LOAD
= 0mA ● 20 45 µA
LOAD
I
= 1mA ● 55 100 µA
LOAD
= 10mA ● 230 400 µA
LOAD
I
= 50mA ● 12 mA
LOAD
I
= 100mA ● 2.2 4 mA
LOAD
= 10µF, C
OUT
= 0.01µF, I
BYP
ADJ Pin Bias Current (Notes 3, 8) 30 100 nA
Shutdown Threshold V
SHDN Pin Current V
(Note 9) V
Quiescent Current in Shutdown VIN = 6V, V
Ripple Rejection (Note 3) VIN – V
Current Limit VIN = 7V, V
Input Reverse Leakage Current VIN = –20V, V
Reverse Output Current LT1761-1.5 V
(Note 10) LT1761-1.8 V
= Off to On ● 0.8 2 V
OUT
V
= On to Off ● 0.25 0.65 V
OUT
= 0V ● 0 0.5 µA
SHDN
= 20V ● 13 µA
SHDN
= 0V 0.01 0.1 µA
SHDN
= 1.5V (Avg), V
OUT
I
= 50mA
LOAD
= 0V 200 mA
= V
OUT(NOMINAL)
OUT
+ 1V, ∆V
= 0V ● 1mA
OUT
= 1.5V, VIN < 1.5V 10 20 µA
OUT
= 1.8V, VIN < 1.8V 10 20 µA
OUT
= 2V, VIN < 2V 10 20 µA
OUT
= 2.5V, VIN < 2.5V 10 20 µA
OUT
= 2.8V, VIN < 2.8V 10 20 µA
OUT
= 3V, VIN < 3V 10 20 µA
OUT
= 3.3V, VIN < 3.3V 10 20 µA
OUT
= 5V, VIN < 5V 10 20 µA
OUT
= 1.22V, VIN < 1.22V 5 10 µA
OUT
V
IN
LT1761-2 V
LT1761-2.5 V
LT1761-2.8 V
LT1761-3 V
LT1761-3.3 V
LT1761-5 V
LT1761 (Note 3) V
= 1mA to 50mA 10 20 mV
LOAD
= 1mA to 50mA ● 40 mV
LOAD
= 1mA to 100mA 20 40 mV
LOAD
= 1mA to 100mA ● 100 mV
LOAD
= 1mA to 50mA 15 30 mV
LOAD
= 1mA to 50mA ● 60 mV
LOAD
= 1mA to 100mA 25 65 mV
LOAD
= 1mA to 100mA ● 150 mV
LOAD
= 1mA to 50mA 1 6 mV
LOAD
= 1mA to 50mA ● 12 mV
LOAD
= 1mA to 100mA 1 12 mV
LOAD
= 1mA to 100mA ● 50 mV
LOAD
= 100mA, BW = 10Hz to 100kHz 20 µV
LOAD
= 0.5V
RIPPLE
= –5% ● 110 mA
OUT
P-P
, f
= 120Hz, 55 65 dB
RIPPLE
RMS
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT1761 regulators are tested and specified under pulse load
conditions such that T
≈ TA. The LT1761 is 100% production tested at
J
4
TA = 25°C. Performance at –40°C and 125°C is assured by design,
characterization and correlation with statistical process controls.
Note 3: The LT1761 (adjustable versions) are tested and specified for
these conditions with the ADJ pin connected to the OUT pin.
Page 5
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE (V)
100
1761 G06
050
1.84
1.83
1.82
1.81
1.80
1.79
1.78
1.77
1.76
–25 25 75 125
IL = 1mA
ELECTRICAL CHARACTERISTICS
LT1761 Series
Note 4: Operating conditions are limited by maximum junction
temperature. The regulated output voltage specification will not apply for
all possible combinations of input voltage and output current. When
operating at maximum input voltage, the output current range must be
limited. When operating at maximum output current, the input voltage
range must be limited.
Note 5: To satisfy requirements for minimum input voltage, the LT1761
(adjustable version) is tested and specified for these conditions with an
external resistor divider (two 250k resistors) for an output voltage of
2.44V. The external resistor divider will add a 5µA DC load on the output.
Note 6: Dropout voltage is the minimum input to output voltage differential
needed to maintain regulation at a specified output current. In dropout, the
output voltage will be equal to: V
– V
IN
DROPOUT
.
Note 7: GND pin current is tested with VIN = V
(whichever is greater) and a current source load. This means the device is
tested while operating in its dropout region or at the minimum input
voltage specification. This is the worst-case GND pin current. The GND pin
current will decrease slightly at higher input voltages.
Note 8: ADJ pin bias current flows into the ADJ pin.
Note 9: SHDN pin current flows into the SHDN pin.
Note 10: Reverse output current is tested with the IN pin grounded and the
OUT pin forced to the rated output voltage. This current flows into the OUT
pin and out the GND pin.
Note 11: For the LT1761, LT1761-1.5, LT1761-1.8 and LT1761-2 dropout
voltage will be limited by the minimum input voltage specification under
some output voltage/load conditions. See the curve of Minimum Input
Voltage in the Typical Performance Characteristics.
UW
TYPICAL PERFOR A CE CHARACTERISTICS
Typical Dropout Voltage
500
450
400
350
300
250
200
150
DROPOUT VOLTAGE (mV)
100
50
0
0 102030
40
OUTPUT CURRENT (mA)
TJ = 125°C
TJ = 25°C
60 70 80 90 100
50
1761 G00
Guaranteed Dropout Voltage
500
= TEST POINTS
450
400
350
300
250
200
150
DROPOUT VOLTAGE (mV)
100
50
0
0 102030
TJ ≤ 125°C
TJ ≤ 25°C
40
50
OUTPUT CURRENT (mA)
60 70 80 90 100
1761 G01
OUT(NOMINAL)
Dropout Voltage
500
450
400
350
300
250
200
150
DROPOUT VOLTAGE (mV)
100
50
0
–50
–25
IL = 100mA
0
TEMPERATURE (°C)
or VIN = 2.3V
IL = 50mA
IL = 10mA
IL = 1mA
50
25
75
100
125
1761 G01.1
40
35
30
25
20
15
10
QUIESCENT CURRENT (µA)
5
0
–50
Quiescent Current
VIN = 6V
= ∞ (250k FOR LT1761-BYP, -SD)
R
L
= 0 (5µA FOR LT1761-BYP, -SD)
I
L
V
= V
SHDN
IN
V
= 0V
SHDN
–25 25 75 125
050
TEMPERATURE (°C)
100
1761 G03
LT1761-1.5
Output Voltage
1.528
IL = 1mA
1.521
1.514
1.507
1.500
1.493
OUTPUT VOLTAGE (V)
1.486
1.479
1.472
–25 25 75 125
–50
050
TEMPERATURE (°C)
LT1761-1.8
Output Voltage
100
1761 G51
5
Page 6
LT1761 Series
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE (V)
100
1761 G12
050
5.08
5.06
5.04
5.02
5.00
4.98
4.96
4.94
4.92
–25 25 75 125
IL = 1mA
TEMPERATURE (°C)
–50
OUTPUT VOLTAGE (V)
100
1761 G52
050
2.84
2.83
2.82
2.81
2.80
2.79
2.78
2.77
2.76
–25 25 75 125
IL = 1mA
UW
TYPICAL PERFOR A CE CHARACTERISTICS
LT1761-2
Output Voltage
2.04
IL = 1mA
2.03
2.02
2.01
2.00
1.99
OUTPUT VOLTAGE (V)
1.98
1.97
1.96
–25 25 75 125
–50
LT1761-3
Output Voltage
3.060
IL = 1mA
3.045
3.030
3.015
3.000
2.985
OUTPUT VOLTAGE (V)
2.970
2.955
2.940
–25 25 75 125
–50
050
TEMPERATURE (°C)
050
TEMPERATURE (°C)
100
100
1761 G07
1761 G09
LT1761-2.5
Output Voltage
2.54
IL = 1mA
2.53
2.52
2.51
2.50
1.49
OUTPUT VOLTAGE (V)
1.48
1.47
1.46
–25 25 75 125
–50
LT1761-3.3
Output Voltage
3.360
IL = 1mA
3.345
3.330
3.315
3.300
3.285
OUTPUT VOLTAGE (V)
3.270
3.255
3.240
–25 25 75 125
–50
050
TEMPERATURE (°C)
050
TEMPERATURE (°C)
LT1761-2.8
Output Voltage
100
1761 G08
LT1761-5
Output Voltage
100
1761 G11
1.240
1.235
1.230
1.225
1.220
1.215
ADJ PIN VOLTAGE (V)
1.210
1.205
1.200
6
LT1761-BYP, LT1761-SD
ADJ Pin Voltage
IL = 1mA
–25 25 75 125
–50
050
TEMPERATURE (°C)
100
1761 G10
LT1761-1.5
Quiescent Current
200
TJ = 25°C
175
= ∞
R
L
150
125
100
75
50
QUIESCENT CURRENT (µA)
25
0
213579
0
V
SHDN
V
SHDN
6
4
INPUT VOLTAGE (V)
= V
= 0V
LT1761-1.8
Quiescent Current
200
TJ = 25°C
175
= ∞
R
L
150
125
100
75
50
QUIESCENT CURRENT (µA)
IN
8
10
1761 G53
25
0
213579
0
INPUT VOLTAGE (V)
V
= V
SHDN
IN
V
= 0V
SHDN
6
8
4
10
1761 G18
Page 7
INPUT VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G02
0123
4
5
678910
TJ = 25°C
*FOR V
OUT
= 1.8V
RL = 18Ω
I
L
= 100mA*
RL = 36Ω
I
L
= 50mA*
RL = 180Ω
I
L
= 10mA*
RL = 1.8k
I
L
= 1mA*
UW
TYPICAL PERFOR A CE CHARACTERISTICS
LT1761 Series
LT1761-2
Quiescent Current
200
TJ = 25°C
175
= ∞
R
L
150
125
100
75
50
QUIESCENT CURRENT (µA)
25
0
213579
0
LT1761-3
Quiescent Current
200
TJ = 25°C
175
= ∞
R
L
150
125
100
75
50
QUIESCENT CURRENT (µA)
25
0
213579
0
V
SHDN
V
SHDN
6
4
INPUT VOLTAGE (V)
V
SHDN
V
SHDN
6
4
INPUT VOLTAGE (V)
= V
= 0V
= V
= 0V
LT1761-2.5
Quiescent Current
200
TJ = 25°C
175
= ∞
R
L
150
125
100
75
50
QUIESCENT CURRENT (µA)
IN
8
10
1761 G19
25
0
213579
0
INPUT VOLTAGE (V)
V
= V
SHDN
IN
V
= 0V
SHDN
6
8
4
10
1761 G13
LT1761-3.3
Quiescent Current
200
TJ = 25°C
175
= ∞
R
L
150
125
100
75
50
QUIESCENT CURRENT (µA)
IN
8
10
1761 G14
25
0
213579
0
INPUT VOLTAGE (V)
V
= V
SHDN
IN
V
= 0V
SHDN
6
8
4
10
1761 G15
LT1761-2.8
Quiescent Current
200
TJ = 25°C
175
= ∞
R
L
150
125
100
75
50
QUIESCENT CURRENT (µA)
25
0
213579
0
LT1761-5
Quiescent Current
200
TJ = 25°C
175
= ∞
R
L
150
125
100
75
50
QUIESCENT CURRENT (µA)
25
0
213579
0
V
SHDN
V
SHDN
6
4
INPUT VOLTAGE (V)
V
SHDN
V
SHDN
6
4
INPUT VOLTAGE (V)
= V
= 0V
= V
= 0V
IN
8
10
1761 G54
IN
8
10
1761 G16
LT1761-BYP, LT1761-SD
Quiescent Current
30
25
20
15
10
QUIESCENT CURRENT (µA)
5
0
02 6 10 14 18
TJ = 25°C
= 250k
R
L
= 5µA
I
L
4 8 12 16
INPUT VOLTAGE (V)
V
SHDN
V
SHDN
= V
= 0V
LT1761-1.5
GND Pin Current
2.50
2.25
2.00
IN
20
1761 G17
1.75
1.50
1.25
1.00
0.75
GND PIN CURRENT (mA)
0.50
0.25
0
RL = 15Ω
= 100mA*
I
L
RL = 1.5k
I
0123
INPUT VOLTAGE (V)
L
= 1mA*
4
5
TJ = 25°C
*FOR V
= 1.5V
OUT
RL = 30Ω
= 50mA*
I
L
RL = 150Ω
= 10mA*
I
L
678910
1761 G55
LT1761-1.8
GND Pin Current
7
Page 8
LT1761 Series
INPUT VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G23
0123
4
5
678910
TJ = 25°C
*FOR V
OUT
= 5V
RL = 50Ω
I
L
= 100mA
RL = 100Ω
I
L
= 50mA*
RL = 500Ω
I
L
= 10mA*
RL = 5k
I
L
= 1mA*
INPUT VOLTAGE (V)
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
GND PIN CURRENT (mA)
1761 G56
0123
4
5
678910
TJ = 25°C
*FOR V
OUT
= 2.8V
RL = 28Ω
I
L
= 100mA
RL = 56Ω
I
L
= 50mA*
RL = 280Ω
I
L
= 10mA*
RL = 2.8k
I
L
= 1mA*
UW
TYPICAL PERFOR A CE CHARACTERISTICS
LT1761-2
GND Pin Current
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
GND PIN CURRENT (mA)
0.50
0.25
0
0123
RL = 20Ω
I
= 100mA*
L
INPUT VOLTAGE (V)
LT1761-3
GND Pin Current
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
GND PIN CURRENT (mA)
0.50
0.25
0
0123
RL = 30Ω
I
RL = 3k
I
INPUT VOLTAGE (V)
RL = 2k
= 1mA*
I
L
4
= 100mA*
L
= 1mA*
L
4
TJ = 25°C
*FOR V
OUT
RL = 40Ω
= 50mA*
I
L
RL = 200Ω
= 10mA*
I
L
678910
5
TJ = 25°C
*FOR V
OUT
RL = 60Ω
I
= 50mA*
L
RL = 300Ω
= 10mA*
I
L
678910
5
= 2V
1761 G04
= 3V
1761 G21
LT1761-2.5
GND Pin Current
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
GND PIN CURRENT (mA)
0.50
0.25
0
0123
RL = 25Ω
I
L
INPUT VOLTAGE (V)
LT1761-3.3
GND Pin Current
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
GND PIN CURRENT (mA)
0.50
0.25
0
0123
INPUT VOLTAGE (V)
= 100mA
RL = 2.5k
= 1mA*
I
L
4
RL = 33Ω
I
= 100mA*
L
RL = 3.3k
= 1mA*
I
L
4
TJ = 25°C
*FOR V
OUT
RL = 50Ω
= 50mA*
I
L
RL = 250Ω
= 10mA*
I
L
678910
5
TJ = 25°C
*FOR V
678910
5
OUT
RL = 66Ω
I
= 50mA*
L
RL = 330Ω
= 10mA*
I
L
= 3.3V
LT1761-2.8
GND Pin Current
= 2.5V
1761 G20
LT1761-5
GND Pin Current
1761 G22
LT1761-BYP, LT1761-SD
GND Pin Current
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
GND PIN CURRENT (mA)
0.50
0.25
0
0123
8
RL = 12.2Ω
I
= 100mA*
L
RL = 1.22k
= 1mA*
I
L
4
5
INPUT VOLTAGE (V)
TJ = 25°C
*FOR V
RL = 24.4Ω
I
L
= 1.22V
OUT
= 50mA*
RL = 122Ω
= 10mA*
I
L
678910
1761 G24
GND Pin Current vs I
2.50
VIN = V
2.25
2.00
1.75
1.50
1.25
1.00
0.75
GND PIN CURRENT (mA)
0.50
0.25
0
OUT(NOMINAL)
0 102030
OUTPUT CURRENT (mA)
+ 1V
40
50
LOAD
60 70 80 90 100
1761 G25
SHDN Pin Threshold
(On-to-Off)
1.0
IL = 1mA
0.9
0.8
0.7
0.6
0.5
0.4
0.3
SHDN PIN THRESHOLD (V)
0.2
0.1
0
–50
0
–25
TEMPERATURE (°C)
50
25
75
100
125
1761 G26
Page 9
UW
TYPICAL PERFOR A CE CHARACTERISTICS
SHDN Pin Threshold
(Off-to-On)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
SHDN PIN THRESHOLD (V)
0.2
0.1
0
–50
–25
0
TEMPERATURE (°C)
IL = 100mA
IL = 1mA
25
50
75
100
125
1761 G27
SHDN Pin Input Current
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
SHDN PIN INPUT CURRENT (µA)
0.1
0
0123
SHDN PIN VOLTAGE (V)
4
678910
5
1761 G28
LT1761 Series
SHDN Pin Input Current
1.4
1.2
1.0
0.8
0.6
0.4
SHDN PIN INPUT CURRENT (µA)
0.2
0
–50
0
–25
TEMPERATURE (°C)
V
= 20V
SHDN
50
25
75
100
125
1761 G29
ADJ Pin Bias Current
100
90
80
70
60
50
40
30
ADJ PIN BIAS CURRENT (nA)
20
10
0
–50
–25
0
25
TEMPERATURE (°C)
50
75
100
125
1761 G30
Current Limit
350
V
= 0V
OUT
= 25°C
T
J
300
250
200
150
100
SHORT-CIRCUIT CURRENT (mA)
50
0
0
2
1
INPUT VOLTAGE (V)
Reverse Output Current Reverse Output Current
REVERSE OUTPUT CURRENT (µA)
25.0
22.5
20.0
17.5
15.0
12.5
10.0
VIN = 0V
V
= 1.22V (LT1761-BYP, -SD)
OUT
V
= 1.5V (LT1761-1.5)
OUT
V
= 1.8V (LT1761-1.8)
OUT
V
= 2V (LT1761-2)
OUT
V
= 2.5V (LT1761-2.5)
OUT
V
= 2.8V (LT1761-2.8)
OUT
V
= 3V (LT1761-3)
OUT
V
= 3.3V (LT1761-3.3)
OUT
V
= 5V (LT1761-5)
OUT
7.5
5.0
2.5
0
–50
–25
0
TEMPERATURE (°C)
100
TJ = 25°C
V
90
IN
CURRENT FLOWS
80
INTO OUTPUT PIN
V
OUT
70
(LT1761-BYP, -SD)
60
50
40
30
LT1761-3
20
REVERSE OUTPUT CURRENT (µA)
10
0
0123
= 0V
= V
ADJ
LT1761-1.5
LT1761-1.8
LT1761-2
LT1761-2.5
LT1761-2.8
OUTPUT VOLTAGE (V)
LT1761-5
4
678910
5
LT1761-BYP
LT1761-SD
LT1761-3.3
1761 G33
4
3
LT1761-BYP,-SD
LT1761-1.5,-1.8,-2,
-2.5,-2.8,-3,-3.3,-5
25
5
50
75
100
6
1761 G31
1761 G34
125
Current Limit
350
300
250
200
150
CURRENT LIMIT (mA)
100
50
7
0
–50
–25
25
0
TEMPERATURE (°C)
VIN = 7V
= 0V
V
OUT
50
75
100
125
1761 G32
Input Ripple Rejection
80
70
LT1761-BYP
60
LT1761-5
50
40
30
RIPPLE REJECTION (dB)
20
10
0
100 100k
10 1k 10k 1M
IL = 100mA
= V
V
IN
1V + 50mV
= 0
C
BYP
C
OUT
FREQUENCY (Hz)
OUT(NOMINAL)
RIPPLE
RMS
C
= 10µF
OUT
= 1µF
+
1761 G35
9
Page 10
LT1761 Series
UW
TYPICAL PERFOR A CE CHARACTERISTICS
LT1761-5
Input Ripple Rejection Input Ripple Rejection
80
C
= 0.01µF
70
60
50
40
30
RIPPLE REJECTION (dB)
20
10
0
10 1k 10k 1M
BYP
C
= 100pF
BYP
IL = 100mA
= V
V
IN
OUT(NOMINAL)
1V + 50mV
= 10µF
C
OUT
100 100k
+
RIPPLE
RMS
FREQUENCY (Hz)
C
BYP
= 1000pF
1761 G36
80
70
60
50
40
30
RIPPLE REJECTION (dB)
VIN = V
20
10
0
–50
OUT (NOMINAL)
1V + 0.5V
P-P
AT f = 120Hz
I
= 50mA
L
–25 25 75 125
050
TEMPERATURE (°C)
RIPPLE
Load Regulation
∆IL = 1mA to 50mA
0
100
1761 G39
LT1761-BYP, -SD
LT1761-1.5
LT1761-1.8
LT1761-2
LT1761-2.5
LT1761-2.8
LT1761-3
LT1761-3.3
LT1761-5
–5
–10
–15
–20
–25
–30
LOAD REGULATION (mV)
–35
–40
–25 25 75 125
–50
050
TEMPERATURE (°C)
LT1761-BYP, LT1761-SD
Minimum Input Voltage
2.5
2.0
1.5
1.0
+
100
1761 G37
0.5
MINIMUM INPUT VOLTAGE (V)
0
–50
–25
0
TEMPERATURE (°C)
IL = 100mA
IL = 50mA
50
25
75
100
125
1761 G38
Load Regulation
∆IL = 1mA to 100mA
0
–10
–20
–30
–40
–50
–60
–70
LOAD REGULATION (mV)
–80
–90
–100
–25 25 75 125
–50
050
TEMPERATURE (°C)
100
1761 G40
LT1761-BYP, -SD
LT1761-1.5
LT1761-1.8
LT1761-2
LT1761-2.5
LT1761-2.8
LT1761-3
LT1761-3.3
LT1761-5
Output Noise Spectral Density
10
LT1761-3.3
LT1761-2.8,-3
LT1761-5
1
LT1761-BYP, -SD
0.1
C
= 10µF
OUT
C
= 0
BYP
= 100mA
I
L
OUTPUT NOISE SPECTRAL DENSITY (µV/√Hz)
0.01
10 1k 10k 100k
100
LT1761-2.5
LT1761-1.5
LT1761-1.8
LT1761-2
FREQUENCY (Hz)
10
1761 G41
Output Noise Spectral Density
10
LT1761-5
1
LT1761-BYP
0.1
C
= 0.01µF
BYP
C
= 10µF
OUT
= 100mA
I
L
OUTPUT NOISE SPECTRAL DENSITY (µV/√Hz)
0.01
10 1k 10k 100k
100
FREQUENCY (Hz)
C
BYP
= 1000pF
C
BYP
= 100pF
1761 G42
RMS Output Noise vs
Bypass Capacitor
140
LT1761-5
)
OUTPUT NOISE (µV
120
100
RMS
80
60
40
20
0
10
LT1761-3.3
LT1761-1.8, -2
LT1761-1.5
100 1k 10k
LT1761-3
LT1761-2.8
C
BYP
C
= 10µF
OUT
= 100mA
I
L
f = 10Hz TO 100kHz
LT1761-2.5
LT1761-BYP
(pF)
1761 G43
Page 11
UW
TYPICAL PERFOR A CE CHARACTERISTICS
LT1761 Series
RMS Output Noise vs
Load Current (10Hz to 11kHz)
160
C
= 10µF
OUT
C
= 0
0
0.01
BYP
= 0.01µF
C
BYP
0.1 1
LOAD CURRENT (mA)
)
OUTPUT NOISE (µV
140
120
RMS
100
80
60
40
20
LT1761-5
10Hz to 100kHz Output Noise
C
BYP
LT1761-5
LT1761-BYP
LT1761-5
LT1761-BYP
10 100
= 1000pF
1761 G44
V
OUT
100µV/DIV
LT1761-5
10Hz to 100kHz Output Noise
C
= 0
BYP
C
= 10µF
OUT
= 100mA 1761 G45
I
L
1ms/DIV
LT1761-5
10Hz to 100kHz Output Noise
C
= 100pF
BYP
V
OUT
100µV/DIV
= 10µF
C
OUT
= 100mA 1761 G46
I
L
1ms/DIV
LT1761-5
10Hz to 100kHz Output Noise
C
= 0.01µF
BYP
V
OUT
100µV/DIV
C
OUT
I
L
LT1761-5 Transient Response
C
0.2
0.1
0
–0.1
DEVIATION (V)
OUTPUT VOLTAGE
–0.2
100
50
(mA)
0
LOAD CURRENT
0 400
= 10µF
= 100mA 1761 G47
= 0
BYP
1ms/DIV
800
1200 1600 2000
TIME (µs)
VIN = 6V
C
= 10µF
IN
C
= 10µF
OUT
1761 G49
V
OUT
100µV/DIV
C
OUT
= 100mA 1761 G48
I
L
LT1761-5 Transient Response
C
BYP
0.04
0.02
0
–0.02
DEVIATION (V)
OUTPUT VOLTAGE
–0.04
100
50
(mA)
0
LOAD CURRENT
0406010020
= 10µF
= 0.01µF
1ms/DIV
80
120 140 180160 200
TIME (µs)
VIN = 6V
C
= 10µF
IN
C
= 10µF
OUT
1761 G50
11
Page 12
LT1761 Series
U
UU
PI FU CTIO S
IN (Pin 1): Input. Power is supplied to the device through
the IN pin. A bypass capacitor is required on this pin if the
device is more than six inches away from the main input
filter capacitor. In general, the output impedance of a
battery rises with frequency, so it is advisable to include a
bypass capacitor in battery-powered circuits. A bypass
capacitor in the range of 1µF to 10µF is sufficient. The
LT1761 regulators are designed to withstand reverse
voltages on the IN pin with respect to ground and the OUT
pin. In the case of a reverse input, which can happen if a
battery is plugged in backwards, the device will act as if
there is a diode in series with its input. There will be no
reverse current flow into the regulator and no reverse
voltage will appear at the load. The device will protect both
itself and the load.
GND (Pin 2): Ground.
SHDN (Pin 3, Fixed/-SD Devices): Shutdown. The SHDN
pin is used to put the LT1761 regulators into a low power
shutdown state. The output will be off when the SHDN pin
is pulled low. The SHDN pin can be driven either by 5V
logic or open-collector logic with a pull-up resistor. The
pull-up resistor is required to supply the pull-up current of
the open-collector gate, normally several microamperes,
and the SHDN pin current, typically 1µA. If unused, the
SHDN pin must be connected to VIN. The device will not
function if the SHDN pin is not connected. For the
LT1761-BYP, the SHDN pin is internally connected to VIN.
BYP (Pins 3/4, Fixed/-BYP Devices): Bypass. The BYP
pin is used to bypass the reference of the LT1761 regulators to achieve low noise performance from the regulator.
The BYP pin is clamped internally to ±0.6V (one VBE) from
ground. A small capacitor from the output to this pin will
bypass the reference to lower the output voltage noise. A
maximum value of 0.01µF can be used for reducing output
voltage noise to a typical 20µV
bandwidth. If not used, this pin must be left unconnected.
ADJ (Pin 4, Adjustable Devices Only): Adjust Pin. For the
adjustable LT1761, this is the input to the error amplifier.
This pin is internally clamped to ±7V. It has a bias current
of 30nA which flows into the pin (see curve of ADJ Pin Bias
Current vs Temperature in the Typical Performance Characteristics section). The ADJ pin voltage is 1.22V referenced
to ground and the output voltage range is 1.22V to 20V.
OUT (Pin 5): Output. The output supplies power to the
load. A minimum output capacitor of 1µF is required to
prevent oscillations. Larger output capacitors will be
required for applications with large transient loads to limit
peak voltage transients. See the Applications Information
section for more information on output capacitance and
reverse output characteristics.
over a 10Hz to 100kHz
RMS
WUUU
APPLICATIO S I FOR ATIO
The LT1761 series are 100mA low dropout regulators with
micropower quiescent current and shutdown. The devices
are capable of supplying 100mA at a dropout voltage of
300mV. Output voltage noise can be lowered to 20µV
over a 10Hz to 100kHz bandwidth with the addition of a
0.01µF reference bypass capacitor. Additionally, the refer-
ence bypass capacitor will improve transient response of
the regulator, lowering the settling time for transient load
conditions. The low operating quiescent current (20µA)
drops to less than 1µA in shutdown. In addition to the low
quiescent current, the LT1761 regulators incorporate several protection features which make them ideal for use in
battery-powered systems. The devices are protected
against both reverse input and reverse output voltages. In
battery backup applications where the output can be held
RMS
12
up by a backup battery when the input is pulled to ground,
the LT1761-X acts like it has a diode in series with its
output and prevents reverse current flow. Additionally, in
dual supply applications where the regulator load is
returned to a negative supply, the output can be pulled
below ground by as much as 20V and still allow the device
to start and operate.
Adjustable Operation
The adjustable version of the LT1761 has an output
voltage range of 1.22V to 20V. The output voltage is set by
the ratio of two external resistors as shown in Figure 1. The
device servos the output to maintain the ADJ pin voltage
at 1.22V referenced to ground. The current in R1 is then
Page 13
WUUU
APPLICATIO S I FOR ATIO
LT1761 Series
equal to 1.22V/R1 and the current in R2 is the current in R1
plus the ADJ pin bias current. The ADJ pin bias current,
30nA at 25°C, flows through R2 into the ADJ pin. The
output voltage can be calculated using the formula in
Figure 1. The value of R1 should be no greater than 250k
to minimize errors in the output voltage caused by the ADJ
pin bias current. Note that in shutdown the output is turned
off and the divider current will be zero. Curves of ADJ
Pin Voltage vs Temperature and ADJ Pin Bias Current
vs Temperature appear in the Typical Performance
Characteristics.
The adjustable device is tested and specified with the ADJ
pin tied to the OUT pin for an output voltage of 1.22V.
Specifications for output voltages greater than 1.22V will
be proportional to the ratio of the desired output voltage to
1.22V: V
/1.22V. For example, load regulation for an
OUT
output current change of 1mA to 100mA is –1mV typical
at V
= 1.22V. At V
OUT
= 12V, load regulation is:
OUT
(12V/1.22V)(–1mV) = –9.8mV
IN
V
IN
LT1761
GND
OUT
ADJ
R2
R1
1761 F01
V
OUT
+
VV
OUT ADJ
VV
ADJ
InA
ADJ
OUTPUT RANGE = 1.22V TO 20V
2
.
.
AT 25 C
R
IR
+
()()
1
R
122 1
=+
=
122
=°
30
2
Typical Performance Characteristics section). However,
regulator start-up time is inversely proportional to the size
of the bypass capacitor, slowing to 15ms with a 0.01µF
bypass capacitor and 10µF output capacitor.
Output Capacitance and Transient Response
The LT1761 regulators are designed to be stable with a
wide range of output capacitors. The ESR of the output
capacitor affects stability, most notably with small
capacitors. A minimum output capacitor of 1µF with an
ESR of 3Ω or less is recommended to prevent oscillations. The LT1761-X is a micropower device and output
transient response will be a function of output capacitance. Larger values of output capacitance decrease the
peak deviations and provide improved transient response
for larger load current changes. Bypass capacitors, used
to decouple individual components powered by the
LT1761-X, will increase the effective output capacitor
value. With larger capacitors used to bypass the reference (for low noise operation), larger values of output
capacitors are needed. For 100pF of bypass capacitance,
2.2µF of output capacitor is recommended. With a 330pF
bypass capacitor or larger, a 3.3µF output capacitor is
recommended. The shaded region of Figure 2 defines the
region over which the LT1761 regulators are stable. The
minimum ESR needed is defined by the amount of
bypass capacitance used, while the maximum ESR is 3Ω.
Figure 1. Adjustable Operation
Bypass Capacitance and Low Noise Performance
The LT1761 regulators may be used with the addition of a
bypass capacitor from V
to the BYP pin to lower output
OUT
voltage noise. A good quality low leakage capacitor is recommended. This capacitor will bypass the reference of the
regulator, providing a low frequency noise pole. The noise
pole provided by this bypass capacitor will lower the output voltage noise to as low as 20µV
with the addition
RMS
of a 0.01µF bypass capacitor. Using a bypass capacitor
has the added benefit of improving transient response.
With no bypass capacitor and a 10µF output capacitor, a
10mA to 100mA load step will settle to within 1% of its final
value in less than 100µs. With the addition of a 0.01µF
bypass capacitor, the output will stay within 1% for a 10mA
to 100mA load step (see LT1761-5 Transient Reponse in
Extra consideration must be given to the use of ceramic
capacitors. Ceramic capacitors are manufactured with a
variety of dielectrics, each with different behavior across
temperature and applied voltage. The most common
4.0
3.5
3.0
2.5
2.0
ESR (Ω)
C
1.5
BYP
C
1.0
0.5
0
1
STABLE REGION
= 0
= 100pF
BYP
C
= 330pF
BYP
C
> 3300pF
BYP
310
245678
OUTPUT CAPACITANCE (µF)
9
1761 F02
Figure 2. Stability
13
Page 14
LT1761 Series
WUUU
APPLICATIO S I FOR ATIO
dielectrics used are Z5U, Y5V, X5R and X7R. The Z5U and
Y5V dielectrics are good for providing high capacitances
in a small package, but exhibit strong voltage and temperature coefficients as shown in Figures 3 and 4. When
used with a 5V regulator, a 10µF Y5V capacitor can exhibit
an effective value as low as 1µF to 2µF over the operating
temperature range. The X5R and X7R dielectrics result in
more stable characteristics and are more suitable for use
as the output capacitor. The X7R type has better stability
across temperature, while the X5R is less expensive and
is available in higher values.
Voltage and temperature coefficients are not the only
sources of problems. Some ceramic capacitors have a
piezoelectric response. A piezoelectric device generates
voltage across its terminals due to mechanical stress,
similar to the way a piezoelectric accelerometer or
20
0
–20
–40
–60
CHANGE IN VALUE (%)
–80
–100
0
26
Figure 3. Ceramic Capacitor DC Bias Characteristics
40
20
0
–20
–40
–60
CHANGE IN VALUE (%)
–80
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
–100
–50
–25 0
Figure 4. Ceramic Capacitor Temperature Characteristics
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
X5R
Y5V
4
8
DC BIAS VOLTAGE (V)
TEMPERATURE (°C)
10
Y5V
50 100 125
25 75
14
12
16
1761 F03
X5R
1761 F04
microphone works. For a ceramic capacitor the stress
can be induced by vibrations in the system or thermal
transients. The resulting voltages produced can cause
appreciable amounts of noise, especially when a ceramic
capacitor is used for noise bypassing. A ceramic capacitor produced Figure 5’s trace in response to light tapping
from a pencil. Similar vibration induced behavior can
masquerade as increased output voltage noise.
LT1761-5
C
= 10µF
OUT
= 0.01µF
C
BYP
= 100mA
I
LOAD
V
OUT
500µV/DIV
100ms/DIV 1761 F05
Figure 5. Noise Resulting from Tapping on a Ceramic Capacitor
Thermal Considerations
The power handling capability of the device will be limited
by the maximum rated junction temperature (125°C). The
power dissipated by the device will be made up of two
components:
1. Output current multiplied by the input/output voltage
differential: (I
)(VIN – V
OUT
OUT
), and
2. GND pin current multiplied by the input voltage:
(I
)(VIN).
GND
The ground pin current can be found by examining the
GND Pin Current curves in the Typical Performance Characteristics section. Power dissipation will be equal to the
sum of the two components listed above.
The LT1761 series regulators have internal thermal limiting designed to protect the device during overload conditions. For continuous normal conditions, the maximum
junction temperature rating of 125°C must not be
exceeded. It is important to give careful consideration to
all sources of thermal resistance from junction to ambient.
Additional heat sources mounted nearby must also be
considered.
For surface mount devices, heat sinking is accomplished
by using the heat spreading capabilities of the PC board
14
Page 15
LT1761 Series
U
WUU
APPLICATIONS INFORMATION
and its copper traces. Copper board stiffeners and plated
through-holes can also be used to spread the heat generated by power devices.
The following table lists thermal resistance for several
different board sizes and copper areas. All measurements
were taken in still air on 3/32" FR-4 board with one ounce
copper.
Table 1. Measured Thermal Resistance
COPPER AREA THERMAL RESISTANCE
TOPSIDE* BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm
2500mm
2500mm
2
2
2
2
2
2500mm
2500mm
2500mm
2500mm
2500mm
2500mm22500mm
1000mm22500mm
2
225mm
2
100mm
2
50mm
*Device is mounted on topside.
Calculating Junction Temperature
Example: Given an output voltage of 3.3V, an input voltage
range of 4V to 6V, an output current range of 0mA to 50mA
and a maximum ambient temperature of 50°C, what will
the maximum junction temperature be?
The power dissipated by the device will be equal to:
I
OUT(MAX)(VIN(MAX)
– V
where,
I
OUT(MAX)
V
IN(MAX)
I
GND
at (I
= 50mA
= 6V
= 50mA, VIN = 6V) = 1mA
OUT
So,
OUT
2
2
2
2
2
) + I
GND(VIN(MAX)
125°C/W
125°C/W
130°C/W
135°C/W
150°C/W
)
Protection Features
The LT1761 regulators incorporate several protection
features which make them ideal for use in battery-powered
circuits. In addition to the normal protection features
associated with monolithic regulators, such as current
limiting and thermal limiting, the devices are protected
against reverse input voltages, reverse output voltages
and reverse voltages from output to input.
Current limit protection and thermal overload protection
are intended to protect the device against current overload
conditions at the output of the device. For normal operation, the junction temperature should not exceed 125°C.
The input of the device will withstand reverse voltages of
20V. Current flow into the device will be limited to less than
1mA (typically less than 100µA) and no negative voltage
will appear at the output. The device will protect both itself
and the load. This provides protection against batteries
which can be plugged in backward.
The output of the LT1761-X can be pulled below ground
without damaging the device. If the input is left open circuit
or grounded, the output can be pulled below ground by
20V. For fixed voltage versions, the output will act like a
large resistor, typically 500kΩ or higher, limiting current
flow to typically less than 100µA. For adjustable versions,
the output will act like an open circuit; no current will flow
out of the pin. If the input is powered by a voltage source,
the output will source the short-circuit current of the
device and will protect itself by thermal limiting. In this
case, grounding the SHDN pin will turn off the device and
stop the output from sourcing the short-circuit current.
P = 50mA(6V – 3.3V) + 1mA(6V) = 0.14W
The thermal resistance will be in the range of 125°C/W to
150°C/W depending on the copper area. So the junction
temperature rise above ambient will be approximately
equal to:
0.14W(150°C/W) = 21.2°C
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
T
= 50°C + 21.2°C = 71.2°C
JMAX
The ADJ pin of the adjustable device can be pulled above
or below ground by as much as 7V without damaging the
device. If the input is left open circuit or grounded, the ADJ
pin will act like an open circuit when pulled below ground
and like a large resistor (typically 100k) in series with a
diode when pulled above ground.
In situations where the ADJ pin is connected to a resistor
divider that would pull the ADJ pin above its 7V clamp
voltage if the output is pulled high, the ADJ pin input
current must be limited to less than 5mA. For example, a
resistor divider is used to provide a regulated 1.5V output
from the 1.22V reference when the output is forced to 20V.
15
Page 16
LT1761 Series
The top resistor of the resistor divider must be chosen to
limit the current into the ADJ pin to less than 5mA when the
ADJ pin is at 7V. The 13V difference between output and
ADJ pin divided by the 5mA maximum current into the ADJ
pin yields a minimum top resistor value of 2.6k.
In circuits where a backup battery is required, several
different input/output conditions can occur. The output
voltage may be held up while the input is either pulled to
ground, pulled to some intermediate voltage or is left open
circuit. Current flow back into the output will follow the
curve shown in Figure 6.
When the IN pin of the LT1761-X is forced below the OUT
pin or the OUT pin is pulled above the IN pin, input current
will typically drop to less than 2µA. This can happen if the
input of the device is connected to a discharged (low
voltage) battery and the output is held up by either a
U
PACKAGE DESCRIPTIO
S5 Package
5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
(0.014 – 0.022)
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DIMENSIONS ARE INCLUSIVE OF PLATING
3. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
4. MOLD FLASH SHALL NOT EXCEED 0.254mm
5. PACKAGE EIAJ REFERENCE IS SC-74A (EIAJ)
0.35 – 0.55
Dimensions in inched (millimeters) unless otherwise noted.
2.60 – 3.00
(0.102 – 0.118)
1.50 – 1.75
(0.059 – 0.069)
0.09 – 0.20
(0.004 – 0.008)
(NOTE 2)
backup battery or a second regulator circuit. The state of
the SHDN pin will have no effect on the reverse output
current when the output is pulled above the input.
100
0.00 – 0.15
(0.00 – 0.006)
0.35 – 0.50
(0.014 – 0.020)
FIVE PLACES (NOTE 2)
TJ = 25°C
V
= 0V
90
IN
CURRENT FLOWS
80
INTO OUTPUT PIN
= V
V
OUT
70
60
50
40
30
20
REVERSE OUTPUT CURRENT (µA)
10
0
ADJ
(LT1761-BYP, -SD)
0123
LT1761-2.5
LT1761-2.8
LT1761-3
LT1761-1.8
LT1761-2
LT1761-1.5
OUTPUT VOLTAGE (V)
4
Figure 6. Reverse Output Current
0.90 – 1.45
(0.035 – 0.057)
0.90 – 1.30
(0.035 – 0.051)
(0.110 – 0.118)
LT1761-BYP
LT1761-SD
LT1761-5
2.80 – 3.00
LT1761-3.3
678910
5
(NOTE 3)
1.90
(0.074)
REF
1761 F06
0.95
(0.037)
REF
S5 SOT-23 0599
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Linear Technology Corporation
16
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear-tech.com
Includes 2.5V Reference and Comparator
500mV Dropout Voltage
Noise
RMS
Noise
RMS
(100kHz BW)
RMS
Noise
RMS
, SOT-223 Package
RMS
, 340mV Dropout Voltage
RMS
1761fa LT/TP 0401 2K REV A • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1999
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