LT1761ES5-2.8 [Linear]
100mA, Low Noise, LDO Micropower Regulators in SOT-23; 100mA时低噪声， LDO微稳压器，采用SOT -23
| 型号： | LT1761ES5-2.8 |
| 厂家： | 
Linear |
| 描述： | 100mA, Low Noise, LDO Micropower Regulators in SOT-23 |
| 文件： | 总16页 (文件大小：247K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1761 Series
100mA, Low Noise,
LDO Micropower
Regulators in SOT-23
U
FEATURES
DESCRIPTIO
The LT®1761 series are micropower, low noise, low
dropout regulators. With an external 0.01µF bypass
capacitor, output noise drops to 20µVRMS over a 10Hz to
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. Quies-
cent current is well controlled, not rising in dropout as it
does with many other regulators.
■
Tiny 5-Lead SOT-23 Package
■
Low Noise: 20µVRMS (10Hz to 100kHz)
■
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,
3V, 3.3V, 5V
■
■
■
Adjustable Output from 1.22V to 20V
Stable with 1µF Output Capacitor
Stable with Aluminum, Tantalum or
Ceramic Capacitors
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.
■
■
■
■
Reverse Battery Protected
No Reverse Current
Internal protection circuitry includes reverse battery pro-
tection, 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,
andasanadjustabledevicewitha1.22Vreferencevoltage.
The LT1761 regulators are available in the 5-lead SOT-23
package.
No Protection Diodes Needed
Overcurrent and UOvertemperature Protected
APPLICATIO S
■
Cellular Phones
Pagers
Battery-Powered Systems
Frequency Synthesizers
■
■
, LTC and LT are registered trademarks of Linear Technology Corporation.
■
■
Wireless Modems
U
TYPICAL APPLICATIO
10Hz to 100kHz Output Noise
5V Low Noise Regulator
5V AT100mA
20µV NOISE
10µF
IN
OUT
BYP
V
RMS
IN
+
5.4V TO
20V
1µF
0.01µF
V
LT1761-5
OUT
20µV
RMS
100µV/DIV
SHDN
GND
1761 TA01
1761 G48
1
LT1761 Series
ABSOLUTE AXI U RATI GS
W W U W
(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
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
U W
U
PACKAGE/ORDER I FOR ATIO
TOP VIEW
TOP VIEW
TOP VIEW
IN 1
GND 2
BYP 3
5 OUT
4 ADJ
IN 1
GND 2
5 OUT
4 ADJ
IN 1
GND 2
5 OUT
4 BYP
SHDN 3
SHDN 3
S5 PACKAGE
5-LEAD PLASTIC SOT-23
S5 PACKAGE
5-LEAD PLASTIC SOT-23
S5 PACKAGE
5-LEAD PLASTIC SOT-23
TJMAX = 150°C, θJA = 250°C/ W
TJMAX = 150°C, θJA = 250°C/ W
TJMAX = 150°C, θJA = 250°C/ W
SEE THE APPLICATIONS INFORMATION SECTION.
SEE THE APPLICATIONS INFORMATION SECTION.
SEE THE APPLICATIONS INFORMATION SECTION.
S5 PART
MARKING
ORDER PART
NUMBER
ORDER PART
NUMBER
S5 PART
MARKING
S5 PART
MARKING
ORDER PART
NUMBER
LTGC
LTGH
LT1761ES5-1.5
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
LT1761ES5-BYP
LT1761ES5-SD
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
= 100mA
MIN
TYP
MAX
UNITS
Minimum Input Voltage (Notes 3, 11)
I
●
1.8
2.3
V
LOAD
Regulated Output Voltage
(Note 4)
LT1761-1.5
LT1761-1.8
LT1761-2
V
= 2V, I
= 1mA
LOAD
1.478
1.457
1.436
1.5
1.5
1.5
1.522
1.538
1.555
V
V
V
IN
2.5V < V < 20V, 1mA < I
< 50mA
●
●
IN
IN
LOAD
LOAD
2.5V < V < 20V, 1mA < I
< 100mA
V
= 2.3V, I
= 1mA
LOAD
1.775
1.750
1.725
1.8
1.8
1.8
1.825
1.845
1.860
V
V
V
IN
2.8V < V < 20V, 1mA < I
< 50mA
< 100mA
●
●
IN
IN
LOAD
LOAD
2.8V < V < 20V, 1mA < I
V
= 2.5V, I
IN
IN
= 1mA
LOAD
1.970
1.945
1.920
2
2
2
2.030
2.045
2.060
V
V
V
IN
3V < V < 20V, 1mA < I
< 50mA
< 100mA
●
●
LOAD
LOAD
3V < V < 20V, 1mA < I
LT1761-2.5
V
= 3V, I
= 1mA
LOAD
2.465
2.435
2.415
2.5
2.5
2.5
2.535
2.565
2.575
V
V
V
IN
3.5V < V < 20V, 1mA < I
< 50mA
< 100mA
●
●
IN
IN
LOAD
LOAD
3.5V < V < 20V, 1mA < I
2
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
(Note 4)
LT1761-2.8
V
= 3.3V, I
= 1mA
LOAD
2.762
2.732
2.706
2.8
2.8
2.8
2.838
2.868
2.884
V
V
V
IN
3.8V < V < 20V, 1mA < I
3.8V < V < 20V, 1mA < I
< 50mA
< 100mA
●
●
IN
LOAD
LOAD
IN
LT1761-3
V
= 3.5V, I
IN
IN
= 1mA
LOAD
2.960
2.930
2.900
3
3
3
3.040
3.070
3.090
V
V
V
IN
4V < V < 20V, 1mA < I
< 50mA
< 100mA
●
●
LOAD
LOAD
4V < V < 20V, 1mA < I
LT1761-3.3
V
= 3.8V, I
= 1mA
LOAD
3.250
3.230
3.190
3.3
3.3
3.3
3.350
3.370
3.400
V
V
V
IN
4.3V < V < 20V, 1mA < I
4.3V < V < 20V, 1mA < I
< 50mA
< 100mA
●
●
IN
LOAD
LOAD
IN
LT1761-5
LT1761
V
= 5.5V, I
IN
= 1mA
LOAD
4.935
4.900
4.850
5
5
5
5.065
5.100
5.120
V
V
V
IN
6V < V < 20V, 1mA < I
6V < V < 20V, 1mA < I
< 50mA
< 100mA
●
●
LOAD
LOAD
IN
ADJ Pin Voltage
(Note 3, 4)
V
= 2V, I
= 1mA
LOAD
1.205
1.190
1.170
1.220
1.220
1.220
1.235
1.250
1.260
V
V
V
IN
2.3V < V < 20V, 1mA < I
2.3V < V < 20V, 1mA < I
< 50mA
< 100mA
●
●
IN
LOAD
LOAD
IN
Line Regulation
LT1761-1.5
LT1761-1.8
LT1761-2
LT1761-2.5
LT1761-2.8
LT1761-3
LT1761-3.3
LT1761-5
LT1761(Note 3) ∆V = 2V to 20V, I
∆V = 2V to 20V, I
= 1mA
●
●
●
●
●
●
●
●
●
1
1
1
1
1
1
1
1
1
10
10
10
10
10
10
10
10
10
mV
mV
mV
mV
mV
mV
mV
mV
mV
IN
LOAD
∆V = 2.3V to 20V, I
= 1mA
= 1mA
IN
LOAD
LOAD
∆V = 2.5V to 20V, I
IN
∆V = 3V to 20V, I
= 1mA
IN
LOAD
∆V = 3.3V to 20V, I
= 1mA
= 1mA
= 1mA
= 1mA
IN
LOAD
LOAD
LOAD
LOAD
∆V = 3.5V to 20V, I
IN
∆V = 3.8V to 20V, I
IN
∆V = 5.5V to 20V, I
IN
= 1mA
IN
LOAD
Load Regulation
LT1761-1.5
LT1761-1.8
LT1761-2
V
V
V
V
= 2.5V, ∆I
= 2.5V, ∆I
= 2.5V, ∆I
= 2.5V, ∆I
= 1mA to 50mA
= 1mA to 50mA
= 1mA to 100mA
= 1mA to 100mA
10
20
35
30
55
mV
mV
mV
mV
IN
IN
IN
IN
LOAD
LOAD
LOAD
LOAD
●
●
14
V
V
V
V
= 2.8V, ∆I
= 2.8V, ∆I
= 2.8V, ∆I
= 2.8V, ∆I
= 1mA to 50mA
= 1mA to 50mA
= 1mA to 100mA
= 1mA to 100mA
10
15
20
35
30
60
mV
mV
mV
mV
IN
IN
IN
IN
LOAD
LOAD
LOAD
LOAD
●
●
V
V
V
V
= 3V, ∆I
= 3V, ∆I
= 3V, ∆I
= 3V, ∆I
= 1mA to 50mA
= 1mA to 50mA
= 1mA to 100mA
= 1mA to 100mA
10
15
20
35
35
65
mV
mV
mV
mV
IN
IN
IN
IN
LOAD
LOAD
LOAD
LOAD
●
●
LT1761-2.5
LT1761-2.8
LT1761-3
V
V
V
V
= 3.5V, ∆I
= 3.5V, ∆I
= 3.5V, ∆I
= 3.5V, ∆I
= 1mA to 50mA
= 1mA to 50mA
= 1mA to 100mA
= 1mA to 100mA
10
20
20
35
40
80
mV
mV
mV
mV
IN
IN
IN
IN
LOAD
LOAD
LOAD
LOAD
●
●
V
V
V
V
= 3.8V, ∆I
= 3.8V, ∆I
= 3.8V, ∆I
= 3.8V, ∆I
= 1mA to 50mA
= 1mA to 50mA
= 1mA to 100mA
= 1mA to 100mA
10
20
20
38
40
86
mV
mV
mV
mV
IN
IN
IN
IN
LOAD
LOAD
LOAD
LOAD
●
●
V
V
V
V
= 4V, ∆I
= 4V, ∆I
= 4V, ∆I
= 4V, ∆I
= 1mA to 50mA
= 1mA to 50mA
= 1mA to 100mA
= 1mA to 100mA
10
20
20
40
40
90
mV
mV
mV
mV
IN
IN
IN
IN
LOAD
LOAD
LOAD
LOAD
●
●
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
Load Regulation
LT1761-3.3
V
V
V
V
= 4.3V, ∆I
= 4.3V, ∆I
= 4.3V, ∆I
= 4.3V, ∆I
= 1mA to 50mA
= 1mA to 50mA
= 1mA to 100mA
= 1mA to 100mA
10
20
40
mV
mV
mV
mV
IN
IN
IN
IN
LOAD
LOAD
LOAD
LOAD
●
●
20
40
100
LT1761-5
V
V
V
V
= 6V, ∆I
= 6V, ∆I
= 6V, ∆I
= 6V, ∆I
= 1mA to 50mA
= 1mA to 50mA
= 1mA to 100mA
= 1mA to 100mA
15
25
30
60
mV
mV
mV
mV
IN
IN
IN
IN
LOAD
LOAD
LOAD
LOAD
●
●
65
150
LT1761 (Note 3) V = 2.3V, ∆I
= 1mA to 50mA
= 1mA to 50mA
= 1mA to 100mA
= 1mA to 100mA
1
1
6
mV
mV
mV
mV
IN
LOAD
LOAD
LOAD
LOAD
V
V
V
= 2.3V, ∆I
= 2.3V, ∆I
= 2.3V, ∆I
●
●
12
12
50
IN
IN
IN
Dropout Voltage
I
I
= 1mA
= 1mA
0.10
0.17
0.24
0.30
0.15
0.19
V
V
LOAD
LOAD
V
= V
●
●
●
●
IN
OUT(NOMINAL)
(Notes 5, 6, 11)
I
I
= 10mA
= 10mA
0.22
0.29
V
V
LOAD
LOAD
I
I
= 50mA
= 50mA
0.28
0.38
V
V
LOAD
LOAD
I
I
= 100mA
= 100mA
0.35
0.45
V
V
LOAD
LOAD
GND Pin Current
I
I
I
I
I
= 0mA
●
●
●
●
●
20
55
230
1
2.2
45
100
400
2
µA
µA
LOAD
LOAD
LOAD
LOAD
LOAD
V
= V
= 1mA
IN
OUT(NOMINAL)
(Notes 5, 7)
= 10mA
= 50mA
= 100mA
µA
mA
mA
4
Output Voltage Noise
ADJ Pin Bias Current
Shutdown Threshold
C
= 10µF, C
= 0.01µF, I
= 100mA, BW = 10Hz to 100kHz
20
30
µV
RMS
OUT
BYP
LOAD
(Notes 3, 8)
100
2
nA
V
V
= Off to On
= On to Off
●
●
0.8
0.65
V
V
OUT
OUT
0.25
SHDN Pin Current
(Note 9)
V
V
= 0V
= 20V
●
●
0
1
0.5
3
µA
µA
SHDN
SHDN
Quiescent Current in Shutdown
Ripple Rejection (Note 3)
V
V
= 6V, V
= 0V
SHDN
0.01
65
0.1
µA
IN
– V
= 1.5V (Avg), V
= 0.5V , f = 120Hz,
P-P RIPPLE
55
dB
IN
OUT
RIPPLE
I
= 50mA
LOAD
Current Limit
V
V
= 7V, V
= 0V
200
mA
mA
IN
IN
OUT
OUT(NOMINAL)
= V
+ 1V, ∆V
= –5%
●
●
110
OUT
Input Reverse Leakage Current
V
= –20V, V
= 0V
OUT
1
mA
IN
Reverse Output Current
(Note 10)
LT1761-1.5
LT1761-1.8
LT1761-2
LT1761-2.5
LT1761-2.8
LT1761-3
LT1761-3.3
LT1761-5
LT1761 (Note 3) V
V
= 1.5V, V < 1.5V
10
10
10
10
10
10
10
10
5
20
20
20
20
20
20
20
20
10
µA
µA
µA
µA
µA
µA
µA
µA
µA
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
OUT
IN
V
= 1.8V, V < 1.8V
IN
V
V
V
V
V
V
= 2V, V < 2V
IN
= 2.5V, V < 2.5V
IN
= 2.8V, V < 2.8V
IN
= 3V, V < 3V
IN
= 3.3V, V < 3.3V
IN
= 5V, V < 5V
IN
= 1.22V, V < 1.22V
IN
T = 25°C. Performance at –40°C and 125°C is assured by design,
characterization and correlation with statistical process controls.
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
A
Note 3: The LT1761 (adjustable versions) are tested and specified for
these conditions with the ADJ pin connected to the OUT pin.
Note 2: The LT1761 regulators are tested and specified under pulse load
conditions such that T ≈ T . The LT1761 is 100% production tested at
J
A
4
LT1761 Series
ELECTRICAL CHARACTERISTICS
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 7: GND pin current is tested with V = V
or V = 2.3V
OUT(NOMINAL) IN
IN
(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.
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
U W
TYPICAL PERFOR A CE CHARACTERISTICS
Typical Dropout Voltage
Dropout Voltage
Guaranteed Dropout Voltage
500
450
400
350
300
250
200
150
100
50
500
450
400
350
300
250
200
150
100
50
500
450
400
350
300
250
200
150
100
50
= TEST POINTS
T
≤ 125°C
≤ 25°C
J
T = 125°C
J
I
= 100mA
L
T
J
I
= 50mA
= 10mA
L
T = 25°C
J
I
L
I
= 1mA
L
0
–50
0
0
0
25
50
75 100 125
–25
40
40
50 60 70 80 90 100
0
10 20 30
50 60 70 80 90 100
0
10 20 30
TEMPERATURE (°C)
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
1761 G01.1
1761 G00
1761 G01
LT1761-1.5
Output Voltage
LT1761-1.8
Output Voltage
Quiescent Current
1.528
1.521
1.514
1.507
1.500
1.493
1.486
1.479
1.472
1.84
1.83
1.82
1.81
1.80
1.79
1.78
1.77
1.76
40
35
30
25
20
15
10
5
I
= 1mA
I = 1mA
L
V
= 6V
L
IN
L
R
= ∞ (250k FOR LT1761-BYP, -SD)
I
= 0 (5µA FOR LT1761-BYP, -SD)
L
V
SHDN
= V
IN
V
= 0V
50
SHDN
25
0
–50
–25
0
25
50
75
125
–25
0
25
50
75
125
–50
100
–50
100
–25
0
75
125
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1761 G51
1761 G06
1761 G03
5
LT1761 Series
TYPICAL PERFOR A CE CHARACTERISTICS
U W
LT1761-2.5
Output Voltage
LT1761-2.8
Output Voltage
LT1761-2
Output Voltage
2.04
2.03
2.02
2.01
2.00
1.99
1.98
1.97
1.96
2.54
2.53
2.52
2.51
2.50
1.49
1.48
1.47
1.46
2.84
2.83
2.82
2.81
2.80
2.79
2.78
2.77
2.76
I
= 1mA
I = 1mA
L
I
= 1mA
L
L
–25
0
25
50
75
125
–25
0
25
50
75
125
–50
100
100
100
–50
100
–25
0
25
50
75
125
–50
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1761 G07
1761 G08
1761 G52
LT1761-3
Output Voltage
LT1761-3.3
Output Voltage
LT1761-5
Output Voltage
5.08
5.06
5.04
5.02
5.00
4.98
4.96
4.94
4.92
3.060
3.045
3.030
3.015
3.000
2.985
2.970
2.955
2.940
3.360
3.345
3.330
3.315
3.300
3.285
3.270
3.255
3.240
I
= 1mA
I
= 1mA
I
= 1mA
L
L
L
–25
0
25
50
75
125
–50
100
–25
0
25
50
75
125
–50
–25
0
25
50
75
125
–50
100
TEMPERATURE (°C)
TEMPERATURE (°C)
TEMPERATURE (°C)
1761 G12
1761 G09
1761 G11
LT1761-1.5
Quiescent Current
LT1761-BYP, LT1761-SD
ADJ Pin Voltage
LT1761-1.8
Quiescent Current
200
175
150
125
100
75
200
175
150
125
100
75
1.240
1.235
1.230
1.225
1.220
1.215
1.210
1.205
1.200
T
= 25°C
= ∞
T
= 25°C
J
R = ∞
L
I = 1mA
L
J
L
R
50
50
V
V
= V
V
V
= V
IN
SHDN
IN
SHDN
25
25
= 0V
8
= 0V
8
SHDN
SHDN
0
0
0
1
2
3
4
5
6
7
9
10
0
1
2
3
4
5
6
7
9
10
–25
0
25
50
75
125
–50
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
TEMPERATURE (°C)
1761 G53
1761 G18
1761 G10
6
LT1761 Series
U W
TYPICAL PERFOR A CE CHARACTERISTICS
LT1761-2
Quiescent Current
LT1761-2.8
Quiescent Current
LT1761-2.5
Quiescent Current
200
175
150
125
100
75
200
175
150
125
100
75
200
175
150
125
100
75
T
= 25°C
= ∞
T
= 25°C
= ∞
T
= 25°C
R = ∞
L
J
L
J
L
J
R
R
50
50
50
V
V
= V
IN
V
= V
IN
SHDN
V
= V
IN
SHDN
SHDN
25
25
25
= 0V
8
V
= 0V
8
V
= 0V
8
SHDN
SHDN
SHDN
0
0
0
0
1
2
3
4
5
6
7
9
10
0
1
2
3
4
5
6
7
9
10
0
1
2
3
4
5
6
7
9
10
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1761 G19
1761 G13
1761 G54
LT1761-3
Quiescent Current
LT1761-3.3
Quiescent Current
LT1761-5
Quiescent Current
200
175
150
125
100
75
200
175
150
125
100
75
200
175
150
125
100
75
T
= 25°C
= ∞
T
= 25°C
R = ∞
L
T
= 25°C
= ∞
J
L
J
J
L
R
R
50
50
50
V
V
= V
IN
V
= V
IN
V
= V
IN
SHDN
SHDN
SHDN
25
25
25
V
= 0V
8
= 0V
8
V
= 0V
8
SHDN
SHDN
SHDN
0
0
0
0
1
2
3
4
5
6
7
9
10
0
1
2
3
4
5
6
7
9
10
0
1
2
3
4
5
6
7
9
10
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1761 G15
1761 G16
1761 G14
LT1761-BYP, LT1761-SD
Quiescent Current
LT1761-1.5
GND Pin Current
LT1761-1.8
GND Pin Current
30
25
20
15
10
5
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
T = 25°C
T = 25°C
T = 25°C
J
R
J
J
= 250k
*FOR V
= 1.5V
*FOR V
= 1.8V
L
L
OUT
OUT
I
= 5µA
V
= V
IN
SHDN
R
L
= 15Ω
R = 18Ω
L
L
I
= 100mA*
I = 100mA*
L
R
L
= 36Ω
L
R
L
= 30Ω
L
I
= 50mA*
I
= 50mA*
R
L
= 1.5k
R = 1.8k
L
I = 1mA*
L
L
R
L
= 150Ω
R
= 180Ω
L
L
I
= 1mA*
I
= 10mA*
I = 10mA*
L
V
SHDN
= 0V
0
0
2
4
6
8
10 12 14 16 18 20
0
1
2
3
4
6
7
8
9
10
0
1
2
3
4
6
7
8
9
10
5
5
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1761 G17
1761 G55
1761 G02
7
LT1761 Series
TYPICAL PERFOR A CE CHARACTERISTICS
U W
LT1761-2
GND Pin Current
LT1761-2.5
GND Pin Current
LT1761-2.8
GND Pin Current
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
T = 25°C
T = 25°C
T = 25°C
J
J
J
*FOR V
= 2.5V
*FOR V
= 2.8V
*FOR V
= 2V
OUT
OUT
OUT
R
L
= 25Ω
L
R
L
= 28Ω
L
I
= 100mA
I
= 100mA
R
L
= 20Ω
L
I
= 100mA*
R
L
= 50Ω
R
L
= 56Ω
L
R
L
= 40Ω
L
L
I
= 50mA*
I
= 50mA*
I
= 50mA*
R
L
= 2.5k
R
L
= 2k
R = 2.8k
L
I = 1mA*
L
L
L
R
L
= 250Ω
R
L
= 200Ω
R
L
= 280Ω
L
L
L
I
= 1mA*
I
= 1mA*
I
= 10mA*
I
= 10mA*
I
= 10mA*
4
4
0
1
2
3
5
6
7
8
9
10
4
0
1
2
3
5
6
7
8
9
10
0
1
2
3
5
6
7
8
9
10
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1761 G20
1761 G04
1761 G56
LT1761-3
GND Pin Current
LT1761-3.3
GND Pin Current
LT1761-5
GND Pin Current
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
T = 25°C
T = 25°C
J
J
T = 25°C
J
*FOR V
= 3V
*FOR V
= 3.3V
OUT
OUT
*FOR V
= 5V
OUT
R
L
= 50Ω
L
I
= 100mA
R
L
= 30Ω
L
R
L
= 33Ω
L
I
= 100mA*
I
= 100mA*
R
L
= 100Ω
L
R
L
= 66Ω
L
R
L
= 60Ω
I
= 50mA*
L
I
= 50mA*
I
= 50mA*
R
L
= 5k
= 1mA*
L
R
L
= 3k
= 1mA*
R = 3.3k
L
L
R
= 500Ω
= 10mA*
R
L
= 300Ω
R
L
= 330Ω
L
L
L
I
I
I
= 1mA*
L
I
I
= 10mA*
I
= 10mA*
L
4
4
5
4
0
1
2
3
5
6
7
8
9
10
0
1
2
3
6
7
8
9
10
0
1
2
3
6
7
8
9
10
5
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
INPUT VOLTAGE (V)
1761 G21
1761 G22
1761 G23
SHDN Pin Threshold
(On-to-Off)
LT1761-BYP, LT1761-SD
GND Pin Current
GND Pin Current vs ILOAD
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
0.25
0
I
L
= 1mA
V
IN
= V
+ 1V
T = 25°C
OUT(NOMINAL)
J
*FOR V
= 1.22V
OUT
R
L
= 12.2Ω
L
I
= 100mA*
R
L
= 24.4Ω
L
I
= 50mA*
R
L
= 1.22k
L
R
L
= 122Ω
L
I
= 1mA*
I
= 10mA*
40
50 60 70 80 90 100
0
10 20 30
4
–50
0
25
50
75
125
0
1
2
3
5
6
7
8
9
10
–25
100
TEMPERATURE (°C)
OUTPUT CURRENT (mA)
INPUT VOLTAGE (V)
1761 G25
1761 G24
1761 G26
8
LT1761 Series
U W
TYPICAL PERFOR A CE CHARACTERISTICS
SHDN Pin Threshold
(Off-to-On)
SHDN Pin Input Current
SHDN Pin Input Current
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
V
= 20V
SHDN
I
= 100mA
L
I
= 1mA
L
–50
0
25
50
75 100 125
–50
–25
0
25
50
75 100 125
–25
4
0
1
2
3
5
6
7
8
9
10
TEMPERATURE (°C)
TEMPERATURE (°C)
SHDN PIN VOLTAGE (V)
1761 G27
1761 G29
1761 G28
Current Limit
Current Limit
ADJ Pin Bias Current
100
90
80
70
60
50
40
30
20
10
0
350
300
250
200
150
100
50
350
300
250
200
150
100
50
V
T
= 0V
V
V
= 7V
OUT
OUT
J
IN
= 25°C
= 0V
0
0
–50
0
25
50
75 100 125
0
1
2
3
4
5
6
7
–50
–25
0
25
50
75 100 125
–25
TEMPERATURE (°C)
INPUT VOLTAGE (V)
TEMPERATURE (°C)
1761 G30
1761 G31
1761 G32
Reverse Output Current
Reverse Output Current
Input Ripple Rejection
80
70
60
50
40
30
20
10
0
25.0
22.5
20.0
17.5
15.0
100
90
80
70
60
50
40
30
20
10
0
V
V
V
V
V
V
V
V
V
= 0V
T = 25°C
IN
LT1761-BYP
LT1761-SD
I
= 100mA
IN
J
V
L
V
= 1.22V (LT1761-BYP, -SD)
= 1.5V (LT1761-1.5)
= 1.8V (LT1761-1.8)
= 2V (LT1761-2)
= 0V
OUT
OUT
OUT
OUT
OUT
OUT
OUT
= V
+
IN
OUT(NOMINAL)
LT1761-BYP
LT1761-5
CURRENT FLOWS
INTO OUTPUT PIN
1V + 50mV
C
RIPPLE
RMS
= 0
BYP
V
= V
ADJ
OUT
= 2.5V (LT1761-2.5)
= 2.8V (LT1761-2.8)
= 3V (LT1761-3)
(LT1761-BYP, -SD)
LT1761-1.5
C
= 10µF
OUT
LT1761-1.8
LT1761-2
LT1761-2.5
= 3.3V (LT1761-3.3)
= 5V (LT1761-5)
12.5 OUT
V
OUT
10.0
7.5
5.0
2.5
0
LT1761-2.8
LT1761-3
LT1761-BYP,-SD
C
= 1µF
OUT
LT1761-1.5,-1.8,-2,
-2.5,-2.8,-3,-3.3,-5
LT1761-3.3
LT1761-5
10
100
1k
10k
100k
1M
4
0
1
2
3
5
6
7
8
9
10
–50
0
25
50
75 100 125
–25
FREQUENCY (Hz)
TEMPERATURE (°C)
OUTPUT VOLTAGE (V)
1761 G35
1761 G33
1761 G34
9
LT1761 Series
U W
TYPICAL PERFOR A CE CHARACTERISTICS
LT1761-5
Input Ripple Rejection
LT1761-BYP, LT1761-SD
Minimum Input Voltage
Input Ripple Rejection
80
70
60
50
40
30
20
10
0
2.5
2.0
1.5
1.0
0.5
0
80
70
60
50
40
30
20
10
0
C
= 0.01µF
BYP
C
= 1000pF
BYP
I
= 100mA
L
I
= 50mA
L
C
= 100pF
BYP
V
= V
+
I
= 100mA
= V
IN
OUT (NOMINAL)
L
IN
1V + 0.5V RIPPLE
P-P
V
+
OUT(NOMINAL)
AT f = 120Hz
1V + 50mV
RMS
RIPPLE
I
= 50mA
–25
C
= 10µF
L
OUT
10
100
1k
10k
100k
1M
0
25
50
75
125
–50
0
25
50
75
125
–50
100
100
–25
FREQUENCY (Hz)
TEMPERATURE (°C)
TEMPERATURE (°C)
1761 G36
1761 G37
1761 G38
Load Regulation
∆IL = 1mA to 50mA
Load Regulation
∆IL = 1mA to 100mA
0
–5
0
–10
LT1761-BYP, -SD
LT1761-1.5
LT1761-BYP, -SD
LT1761-1.5
LT1761-1.8
LT1761-2
–20
–30
–40
–50
–60
–70
–80
–90
–100
–10
–15
–20
–25
–30
–35
–40
LT1761-1.8
LT1761-2
LT1761-2.5
LT1761-2.8
LT1761-3
LT1761-2.5
LT1761-2.8
LT1761-3
LT1761-3.3
LT1761-3.3
LT1761-5
LT1761-5
–25
0
25
50
75
125
–25
0
25
50
75
125
–50
100
–50
100
TEMPERATURE (°C)
TEMPERATURE (°C)
1761 G39
1761 G40
RMS Output Noise vs
Bypass Capacitor
Output Noise Spectral Density
Output Noise Spectral Density
140
120
100
80
10
1
10
1
C
I
= 10µF
OUT
L
LT1761-5
LT1761-3.3
LT1761-3
LT1761-2.8
LT1761-2.5
= 100mA
LT1761-3.3
f = 10Hz TO 100kHz
LT1761-2.8,-3
LT1761-2.5
LT1761-5
LT1761-5
C
= 1000pF
BYP
C
= 100pF
BYP
LT1761-BYP, -SD
60
LT1761-BYP
LT1761-1.5
0.1
0.01
LT1761-1.8
LT1761-2
0.1
C
= 0.01µF
BYP
40
LT1761-1.8, -2
LT1761-1.5
C
C
L
= 10µF
OUT
BYP
20
C
= 10µF
OUT
= 0
LT1761-BYP
1k
I = 100mA
L
I = 100mA
0
0.01
10
100
10k
10
100
1k
FREQUENCY (Hz)
10k
100k
10
100
1k
FREQUENCY (Hz)
10k
100k
C
(pF)
BYP
1761 G41
1761 G42
1761 G43
10
LT1761 Series
U W
TYPICAL PERFOR A CE CHARACTERISTICS
LT1761-5
10Hz to 100kHz Output Noise
CBYP = 100pF
LT1761-5
RMS Output Noise vs
Load Current (10Hz to 11kHz)
10Hz to 100kHz Output Noise
CBYP = 0
160
140
120
100
80
C
= 10µF
OUT
C
= 0
BYP
BYP
C
= 0.01µF
LT1761-5
VOUT
100µV/DIV
VOUT
100µV/DIV
LT1761-BYP
LT1761-5
60
40
1ms/DIV
COUT = 10µF
IL = 100mA
1ms/DIV
20
C
OUT = 10µF
LT1761-BYP
10 100
1761 G46
IL = 100mA
1761 G45
0
0.01
0.1
1
LOAD CURRENT (mA)
1761 G44
LT1761-5
10Hz to 100kHz Output Noise
CBYP = 1000pF
LT1761-5
10Hz to 100kHz Output Noise
CBYP = 0.01µF
VOUT
100µV/DIV
VOUT
100µV/DIV
1ms/DIV
COUT = 10µF
IL = 100mA
1ms/DIV
COUT = 10µF
IL = 100mA
1761 G47
1761 G48
LT1761-5 Transient Response
CBYP = 0
LT1761-5 Transient Response
CBYP = 0.01µF
V
C
C
= 6V
IN
IN
V
C
C
= 6V
IN
IN
0.04
0.02
0
0.2
0.1
= 10µF
= 10µF
= 10µF
OUT
= 10µF
OUT
0
–0.02
–0.04
–0.1
–0.2
100
50
0
100
50
0
80
0
20 40 60
100 120 140 160 180 200
800
TIME (µs)
0
400
1200
1600
2000
TIME (µs)
1761 G50
1761 G49
11
LT1761 Series
U
U
U
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.
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 regula-
tors 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
maximumvalueof0.01µFcanbeusedforreducingoutput
voltage noise to a typical 20µVRMS over a 10Hz to 100kHz
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
of30nAwhichflowsintothepin(seecurveofADJPinBias
Current vs Temperature in the Typical Performance Char-
acteristicssection).TheADJpinvoltageis1.22Vreferenced
to ground and the output voltage range is 1.22V to 20V.
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
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.
W U U
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APPLICATIO S I FOR ATIO
TheLT1761seriesare100mAlowdropoutregulatorswith
micropowerquiescentcurrentandshutdown.Thedevices
are capable of supplying 100mA at a dropout voltage of
300mV. Output voltage noise can be lowered to 20µVRMS
over a 10Hz to 100kHz bandwidth with the addition of a
0.01µFreferencebypasscapacitor. Additionally, therefer-
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
quiescentcurrent, theLT1761regulatorsincorporatesev-
eral 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
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
theratiooftwoexternalresistorsasshowninFigure1.The
device servos the output to maintain the ADJ pin voltage
at 1.22V referenced to ground. The current in R1 is then
12
LT1761 Series
W U U
APPLICATIO S I FOR ATIO
U
equalto1.22V/R1andthecurrentinR2isthecurrentinR1
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
pinbiascurrent.Notethatinshutdowntheoutputisturned
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.
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 oscilla-
tions. The LT1761-X is a micropower device and output
transient response will be a function of output capaci-
tance. Larger values of output capacitance decrease the
peakdeviationsandprovideimprovedtransientresponse
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 refer-
ence (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. TheshadedregionofFigure2definesthe
region over which the LT1761 regulators are stable. The
minimum ESR needed is defined by the amount of
bypasscapacitanceused,whilethemaximumESRis3Ω.
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: VOUT/1.22V. For example, load regulation for an
output current change of 1mA to 100mA is –1mV typical
at VOUT = 1.22V. At VOUT = 12V, load regulation is:
(12V/1.22V)(–1mV) = –9.8mV
IN
OUT
ADJ
V
OUT
R2
R1
V
= 1.22V 1+
= 1.22V
+ I
(
R2
+
)(
)
OUT
ADJ
V
IN
R2
R1
LT1761
GND
V
ADJ
I
= 30nA AT 25°C
ADJ
OUTPUT RANGE = 1.22V TO 20V
1761 F01
Figure 1. Adjustable Operation
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
Bypass Capacitance and Low Noise Performance
The LT1761 regulators may be used with the addition of a
bypass capacitor from VOUT to the BYP pin to lower output
voltage noise. A good quality low leakage capacitor is rec-
ommended. Thiscapacitorwillbypassthereferenceofthe
regulator, providing a low frequency noise pole. The noise
pole provided by this bypass capacitor will lower the out-
put voltage noise to as low as 20µVRMS with the addition
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
10mAto100mAloadstepwillsettletowithin1%ofitsfinal
value in less than 100µs. With the addition of a 0.01µF
bypasscapacitor,theoutputwillstaywithin1%fora10mA
to 100mA load step (see LT1761-5 Transient Reponse in
4.0
3.5
3.0
STABLE REGION
2.5
2.0
C
= 0
1.5
1.0
0.5
0
BYP
C
= 100pF
BYP
C
= 330pF
BYP
C
> 3300pF
BYP
1
3
6
9 10
8
2
4
5
7
OUTPUT CAPACITANCE (µF)
1761 F02
Figure 2. Stability
13
LT1761 Series
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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 tem-
perature 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.
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 capaci-
tor 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
OUT = 10µF
CBYP = 0.01µF
ILOAD = 100mA
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
VOUT
500µV/DIV
100ms/DIV
1761 F05
20
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
Figure 5. Noise Resulting from Tapping on a Ceramic Capacitor
0
X5R
Thermal Considerations
–20
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:
–40
–60
Y5V
–80
1. Output current multiplied by the input/output voltage
differential: (IOUT)(VIN – VOUT), and
–100
0
8
12 14
2
4
6
10
16
DC BIAS VOLTAGE (V)
2. GND pin current multiplied by the input voltage:
(IGND)(VIN).
1761 F03
Figure 3. Ceramic Capacitor DC Bias Characteristics
The ground pin current can be found by examining the
GND Pin Current curves in the Typical Performance Char-
acteristics section. Power dissipation will be equal to the
sum of the two components listed above.
40
20
X5R
0
–20
The LT1761 series regulators have internal thermal limit-
ing designed to protect the device during overload condi-
tions. For continuous normal conditions, the maximum
junction temperature rating of 125°C must not be
exceeded. It is important to give careful consideration to
allsourcesofthermalresistancefromjunctiontoambient.
Additional heat sources mounted nearby must also be
considered.
–40
Y5V
–60
–80
BOTH CAPACITORS ARE 16V,
1210 CASE SIZE, 10µF
–100
50
TEMPERATURE (°C)
100 125
–50 –25
0
25
75
1761 F04
For surface mount devices, heat sinking is accomplished
by using the heat spreading capabilities of the PC board
Figure 4. Ceramic Capacitor Temperature Characteristics
14
LT1761 Series
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W U U
APPLICATIONS INFORMATION
and its copper traces. Copper board stiffeners and plated
through-holes can also be used to spread the heat gener-
ated by power devices.
Protection Features
The LT1761 regulators incorporate several protection
featureswhichmakethemidealforuseinbattery-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.
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
Current limit protection and thermal overload protection
areintendedtoprotectthedeviceagainstcurrentoverload
conditions at the output of the device. For normal opera-
tion, the junction temperature should not exceed 125°C.
COPPER AREA
THERMAL RESISTANCE
TOPSIDE*
2500mm2
1000mm2
225mm2
100mm2
50mm2
BACKSIDE BOARD AREA (JUNCTION-TO-AMBIENT)
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
2500mm2
125°C/W
125°C/W
130°C/W
135°C/W
150°C/W
The input of the device will withstand reverse voltages of
20V.Currentflowintothedevicewillbelimitedtolessthan
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.
*Device is mounted on topside.
Calculating Junction Temperature
Example: Given an output voltage of 3.3V, an input voltage
rangeof4Vto6V, anoutputcurrentrangeof0mAto50mA
and a maximum ambient temperature of 50°C, what will
the maximum junction temperature be?
The output of the LT1761-X can be pulled below ground
withoutdamagingthedevice.Iftheinputisleftopencircuit
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.
The power dissipated by the device will be equal to:
IOUT(MAX)(VIN(MAX) – VOUT) + IGND(VIN(MAX)
where,
)
IOUT(MAX) = 50mA
VIN(MAX) = 6V
IGND at (IOUT = 50mA, VIN = 6V) = 1mA
So,
The ADJ pin of the adjustable device can be pulled above
or below ground by as much as 7V without damaging the
device. Iftheinputisleftopencircuitorgrounded, theADJ
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.
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
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
fromthe1.22Vreferencewhentheoutputisforcedto20V.
The maximum junction temperature will then be equal to
the maximum junction temperature rise above ambient
plus the maximum ambient temperature or:
TJMAX = 50°C + 21.2°C = 71.2°C
15
LT1761 Series
The top resistor of the resistor divider must be chosen to
limitthecurrentintotheADJpintolessthan5mAwhenthe
ADJ pin is at 7V. The 13V difference between output and
ADJpindividedbythe5mAmaximumcurrentintotheADJ
pin yields a minimum top resistor value of 2.6k.
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
T
= 25°C
LT1761-BYP
LT1761-SD
J
90
80
70
60
50
40
30
20
10
0
V = 0V
IN
CURRENT FLOWS
INTO OUTPUT PIN
V
(LT1761-BYP, -SD)
LT1761-1.5
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, pulledtosomeintermediatevoltageorisleftopen
circuit. Current flow back into the output will follow the
curve shown in Figure 6.
= V
ADJ
OUT
LT1761-1.8
LT1761-2
LT1761-2.5
LT1761-2.8
LT1761-3
LT1761-3.3
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
LT1761-5
4
0
1
2
3
5
6
7
8
9
10
OUTPUT VOLTAGE (V)
1761 F06
Figure 6. Reverse Output Current
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PACKAGE DESCRIPTIO
Dimensions in inched (millimeters) unless otherwise noted.
2.60 – 3.00
(0.102 – 0.118)
2.80 – 3.00
1.50 – 1.75
(0.059 – 0.069)
(0.110 – 0.118)
(NOTE 3)
0.00 – 0.15
(0.00 – 0.006)
0.90 – 1.45
(0.035 – 0.057)
S5 Package
5-Lead Plastic SOT-23
(LTC DWG # 05-08-1633)
0.35 – 0.55
(0.014 – 0.022)
0.35 – 0.50
(0.014 – 0.020)
FIVE PLACES (NOTE 2)
0.90 – 1.30
(0.035 – 0.051)
0.09 – 0.20
(0.004 – 0.008)
(NOTE 2)
0.95
(0.037)
REF
S5 SOT-23 0599
1.90
(0.074)
REF
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)
RELATED PARTS
PART NUMBER
LT1120
DESCRIPTION
COMMENTS
Includes 2.5V Reference and Comparator
125mA Low Dropout Regulator with 20µA I
Q
LT1121
150mA Micropower Low Dropout Regulator
30µA I , SOT-223 Package
Q
LT1129
700mA Micropower Low Dropout Regulator
50µA Quiescent Current
LT1175
500mA Negative Low Dropout Micropower Regulator
300mA Low Dropout Micropower Regulator with Shutdown
45µA I , 0.26V Dropout Voltage, SOT-223 Package
Q
LT1521
15µA I , Reverse Battery Protection
Q
LT1529
3A Low Dropout Regulator with 50µA I
500mV Dropout Voltage
Q
LT1762 Series
LT1763 Series
LTC1928
LT1962 Series
LT1963
150mA, Low Noise, LDO Micropower Regulator
500mA, Low Noise, LDO Micropower Regulator
Doubler Charge Pump with Low Noise Linear Regulator
300mA, Low Noise, LDO Micropower Regulator
1.5A, Low Noise, Fast Transient Response LDO
3A, Low Noise, Fast Transient Response LDO
25µA Quiescent Current, 20µV
30µA Quiescent Current, 20µV
Noise
Noise
RMS
RMS
Low Output Noise: 60µV
(100kHz BW)
RMS
30µA Quiescent Current, 20µV
Noise
RMS
40µV
40µV
, SOT-223 Package
RMS
LT1764
, 340mV Dropout Voltage
RMS
LTC3404
High Efficiency Synchronous Step-Down Switching Regulator
Burst ModeTM Operation, Monolithic, 100% Duty Cycle
Burst Mode is a trademark of Linear Technology Corporation.
1761fa LT/TP 0401 2K REV A • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1999
LinearTechnology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
16
●
●
(408)432-1900 FAX:(408)434-0507 www.linear-tech.com
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