1
LT1764A Series
1764af
3A, Fast Transient
Response, Low Noise,
LDO Regulators
s
Optimized for Fast Transient Response
s
Output Current: 3A
s
Dropout Voltage: 340mV at 3A
s
Low Noise: 40
V
RMS
(10Hz to 100kHz)
s
1mA Quiescent Current
s
Wide Input Voltage Range: 2.7V to 20V
s
No Protection Diodes Needed
s
Controlled Quiescent Current in Dropout
s
Fixed Output Voltages: 1.5V, 1.8V, 2.5V, 3.3V
s
Adjustable Output from 1.21V to 20V
s
< 1
A Quiescent Current in Shutdown
s
Stable with 10
F Output Capacitor
s
Stable with Ceramic Capacitors
s
Reverse Battery Protection
s
No Reverse Current
s
Thermal Limiting
The LT
1764A is a low dropout regulator optimized for
fast transient response. The device is capable of supplying
3A of output current with a dropout voltage of 340mV.
Operating quiescent current is 1mA, dropping to < 1
A in
shutdown. Quiescent current is well controlled; it does not
rise in dropout as it does with many other regulators. In
addition to fast transient response, the LT1764A has very
low output voltage noise which makes the device ideal for
sensitive RF supply applications.
Output voltage range is from 1.21V to 20V. The LT1764A
regulators are stable with output capacitors as low as 10
F.
Small ceramic capacitors can be used without the neces-
sary addition of ESR as is common with other regulators.
Internal protection circuitry includes reverse battery pro-
tection, current limiting, thermal limiting and reverse cur-
rent protection. The device is available in fixed output
voltages of 1.5V, 1.8V, 2.5V, 3.3V and as an adjustable
device with a 1.21V reference voltage. The LT1764A regu-
lators are available in 5-lead TO-220 and DD packages.
Dropout Voltage
3.3V
IN
to 2.5V
OUT
Regulator
s
3.3V to 2.5V Logic Power Supply
s
Post Regulator for Switching Supplies
, LTC and LT are registered trademarks of Linear Technology Corporation.
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
IN
SHDN
10
F*
*TANTALUM,
CERAMIC OR
ALUMINUM ELECTROLYTIC
1764 TA01
OUT
V
IN
> 3V
SENSE
GND
LT1764A-2.5
2.5V
3A
10
F*
+
+
LOAD CURRENT (A)
0
0.5
DROPOUT VOLTAGE (mV)
1.0
2.0
1.5
2.5
3.0
1764 TA02
400
350
300
250
200
150
100
50
0
2
LT1764A Series
1764af
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Minimum Input Voltage
I
LOAD
= 0.5A
1.7
V
(Notes 3, 11)
I
LOAD
= 1.5A
1.9
V
I
LOAD
= 3A
q
2.3
2.7
V
Regulated Output Voltage
LT1764A-1.5 V
IN
= 2.21V, I
LOAD
= 1mA
1.477
1.500
1.523
V
(Note 4)
2.7V < V
IN
< 20V, 1mA < I
LOAD
< 3A
q
1.447
1.500
1.545
V
LT1764A-1.8 V
IN
= 2.3V, I
LOAD
= 1mA
1.773
1.800
1.827
V
2.8V < V
IN
< 20V, 1mA < I
LOAD
< 3A
q
1.737
1.800
1.854
V
LT1764A-2.5 V
IN
= 3V, I
LOAD
= 1mA
2.462
2.500
2.538
V
3.5V < V
IN
< 20V, 1mA < I
LOAD
< 3A
q
2.412
2.500
2.575
V
LT1764A-3.3 V
IN
= 3.8V, I
LOAD
= 1mA
3.250
3.300
3.350
V
4.3V < V
IN
< 20V, 1mA < I
LOAD
< 3A
q
3.183
3.300
3.400
V
ADJ Pin Voltage
LT1764A
V
IN
= 2.21V, I
LOAD
= 1mA
1.192
1.210
1.228
V
(Notes 3, 4)
2.7V < V
IN
< 20V, 1mA < I
LOAD
< 3A
q
1.168
1.210
1.246
V
Line Regulation
LT1764A-1.5
V
IN
= 2.21V to 20V, I
LOAD
= 1mA
q
2.5
10
mV
LT1764A-1.8
V
IN
= 2.3V to 20V, I
LOAD
= 1mA
q
3
10
mV
LT1764A-2.5
V
IN
= 3V to 20V, I
LOAD
= 1mA
q
4
10
mV
LT1764A-3.3
V
IN
= 3.8V to 20V, I
LOAD
= 1mA
q
4.5
10
mV
LT1764A (Note 3)
V
IN
= 2.21V to 20V, I
LOAD
= 1mA
q
2
10
mV
ABSOLUTE
M
AXI
M
U
M
RATINGS
W
W
W
U
PACKAGE/ORDER I
N
FOR
M
ATIO
N
W
U
U
(Note 1)
IN Pin Voltage ........................................................
20V
OUT Pin Voltage ....................................................
20V
Input to Output Differential Voltage (Note 12) .......
20V
SENSE Pin Voltage ...............................................
20V
ADJ Pin Voltage ......................................................
7V
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25
C. (Note 2)
ELECTRICAL CHARACTERISTICS
ORDER PART
NUMBER
LT1764AEQ
LT1764AEQ-1.5
LT1764AEQ-1.8
LT1764AEQ-2.5
LT1764AEQ-3.3
T
JMAX
= 150
C,
JA
= 30
C/ W
SHDN Pin Voltage .................................................
20V
Output Short-Circuit Duration ......................... Indefinite
Operating Junction Temperature Range 40
C to 125
C
Storage Temperature Range ................. 65
C to 150
C
Lead Temperature (Soldering, 10 sec).................. 300
C
*PIN 5 = SENSE FOR LT1764A-1.5/LT1764A1.8/
LT1764A-2.5/LT1764A-3.3
= ADJ FOR LT1764A
ORDER PART
NUMBER
Q PACKAGE
5-LEAD PLASTIC DD
TAB IS
GND
FRONT VIEW
SENSE/ADJ*
OUT
GND
IN
SHDN
5
4
3
2
1
LT1764AET
LT1764AET-1.5
LT1764AET-1.8
LT1764AET-2.5
LT1764AET-3.3
*PIN 5 = SENSE FOR LT1764A-1.5/ LT1764A-1.8/
LT1764A-2.5/LT1764A-3.3
= ADJ FOR LT1764A
T
JMAX
= 150
C,
JA
= 50
C/ W
T PACKAGE
5-LEAD PLASTIC TO-220
FRONT VIEW
5
4
3
2
1
TAB IS
GND
SENSE/ADJ*
OUT
GND
IN
SHDN
Consult LTC Marketing for parts specified with wider operating temperature ranges.
3
LT1764A Series
1764af
Load Regulation
LT1764A-1.5
V
IN
= 2.7V,
I
LOAD
= 1mA to 3A
3
7
mV
V
IN
= 2.7V,
I
LOAD
= 1mA to 3A
q
23
mV
LT1764A-1.8
V
IN
= 2.8V,
I
LOAD
= 1mA to 3A
4
8
mV
V
IN
= 2.8V,
I
LOAD
= 1mA to 3A
q
25
mV
LT1764A-2.5
V
IN
= 3.5V,
I
LOAD
= 1mA to 3A
4
10
mV
V
IN
= 3.5V,
I
LOAD
= 1mA to 3A
q
30
mV
LT1764A-3.3
V
IN
= 4.3V,
I
LOAD
= 1mA to 3A
4
12
mV
V
IN
= 4.3V,
I
LOAD
= 1mA to 3A
q
40
mV
LT1764A (Note 3) V
IN
= 2.7V,
I
LOAD
= 1mA to 3A
2
5
mV
V
IN
= 2.7V,
I
LOAD
= 1mA to 3A
q
20
mV
Dropout Voltage
I
LOAD
= 1mA
0.02
0.05
V
V
IN
= V
OUT(NOMINAL)
I
LOAD
= 1mA
q
0.10
V
(Notes 5, 6, 11)
I
LOAD
= 100mA
0.07
0.13
V
I
LOAD
= 100mA
q
0.18
V
I
LOAD
= 500mA
0.14
0.20
V
I
LOAD
= 500mA
q
0.27
V
I
LOAD
= 1.5A
0.25
0.33
V
I
LOAD
= 1.5A
q
0.40
V
I
LOAD
= 3A
0.34
0.45
V
I
LOAD
= 3A
q
0.66
V
GND Pin Current
I
LOAD
= 0mA
q
1
1.5
mA
V
IN
= V
OUT(NOMINAL)
+ 1V
I
LOAD
= 1mA
q
1.1
1.6
mA
(Notes 5, 7)
I
LOAD
= 100mA
q
3.5
5
mA
I
LOAD
= 500mA
q
11
18
mA
I
LOAD
= 1.5A
q
40
75
mA
I
LOAD
= 3A
q
120
200
mA
Output Voltage Noise
C
OUT
= 10
F, I
LOAD
= 3A, BW = 10Hz to 100kHz
40
V
RMS
ADJ Pin Bias Current
(Notes 3, 8)
3
10
A
Shutdown Threshold
V
OUT
= Off to On
q
0.9
2
V
V
OUT
= On to Off
q
0.25
0.75
V
SHDN Pin Current
V
SHDN
= 0V
0.01
1
A
(Note 9)
V
SHDN
= 20V
7
30
A
Quiescent Current in Shutdown
V
IN
= 6V, V
SHDN
= 0V
0.01
1
A
Ripple Rejection
V
IN
V
OUT
= 1.5V (Avg), V
RIPPLE
= 0.5V
P-P
,
55
63
dB
f
RIPPLE
= 120Hz, I
LOAD
= 1.5A
Current Limit
V
IN
= 7V, V
OUT
= 0V
4
A
LT1764A-1.8, LT1764A-2.5, LT1764A-3.3;
q
3.1
A
V
IN
= V
OUT(NOMINAL)
+ 1V,
V
OUT
= 0.1V
LT1764A, LT1764A-1.5;
q
3.1
A
V
IN
= 2.7V,
V
OUT
= 0.1V
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25
C. (Note 2)
4
LT1764A Series
1764af
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT1764A regulators are tested and specified under pulse load
conditions such that T
J
T
A
. The LT1764A is 100% tested at T
A
= 25
C.
Performance at 40
C and 125
C is assured by design, characterization
and correlation with statistical process controls.
Note 3: The LT1764A (adjustable version) is tested and specified for these
conditions with the ADJ pin connected to the OUT pin.
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 LT1764A
(adjustable version) is tested and specified for these conditions with an
external resistor divider (two 4.12k resistors) for an output voltage of
2.42V. The external resistor divider will add a 300
A 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
IN
V
DROPOUT
.
Note 7: GND pin current is tested with V
IN
= V
OUT(NOMINAL)
+ 1V or
V
IN
= 2.7V (whichever is greater) and a current source load. The GND pin
current will decrease 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 LT1764A, LT1764A-1.5 and LT1764A-1.8 dropout voltage
will be limited by the minimum input voltage specification under some
output voltage/load conditions.
Note 12. All combinations of absolute maximum input voltage and
absolute maximum output voltage cannot be achieved. The absolute
maximum differential from input to output is
20V. For example, with
V
IN
= 20V, V
OUT
cannot be pulled below ground.
Input Reverse Leakage Current
V
IN
= 20V, V
OUT
= 0V
q
1
mA
Reverse Output Current (Note 10) LT1764A-1.5 V
OUT
= 1.5V, V
IN
< 1.5V
600
1200
A
LT1764A-1.8 V
OUT
= 1.8V, V
IN
< 1.8V
600
1200
A
LT1764A-2.5 V
OUT
= 2.5V, V
IN
< 2.5V
600
1200
A
LT1764A-3.3 V
OUT
= 3.3V, V
IN
< 3.3V
600
1200
A
LT1764A (Note 3) V
OUT
= 1.21V, V
IN
< 1.21V
300
600
A
ELECTRICAL CHARACTERISTICS
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25
C. (Note 2)
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Typical Dropout Voltage
OUTPUT CURRENT (A)
0
0
DROPOUT VOLTAGE (mV)
100
200
300
400
600
0.5
1.0
1.5
2.0
1764 G01
2.5
3.0
500
T
J
= 125
C
T
J
= 25
C
Guaranteed Dropout Voltage
OUTPUT CURRENT (A)
0
700
600
500
400
300
200
100
0
1.5
2.5
1764 G02
0.5
1.0
2.0
3.0
GUARANTEED DROPOUT VOLTAGE (mV)
= TEST POINTS
T
J
125
C
T
J
25
C
TEMPERATURE (
C)
50
DROPOUT VOLTAGE (mV)
400
500
600
25
75
1764 G03
300
200
25
0
50
100
125
100
0
I
L
= 3A
I
L
= 1.5A
I
L
= 0.5A
I
L
= 100mA
I
L
= 1mA
Dropout Voltage
5
LT1764A Series
1764af
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
Quiescent Current
LT1764A-1.8 Output Voltage
TEMPERATURE (
C)
50
0.8
1.0
1.4
25
75
1764 G04
0.6
0.4
25
0
50
100
125
0.2
0
1.2
QUIESCENT CURRENT (mA)
LT1764A-1.5/1.8/2.5/3.3
LT1764A
V
IN
= 6V
R
L
=
I
L
= 0
V
SHDN
= V
IN
TEMPERATURE (
C)
50
OUTPUT VOLTAGE (V)
25
1756 G05
25
0
50
1.84
1.83
1.82
1.81
1.80
1.79
1.78
1.77
1.76
75
100
125
I
L
= 1mA
LT1764A-3.3 Output Voltage
LT1764A ADJ Pin Voltage
LT1764A-1.8 Quiescent Current
TEMPERATURE (
C)
50
OUTPUT VOLTAGE (V)
25
1756 G07
25
0
50
3.38
3.36
3.34
3.32
3.30
3.28
3.26
3.24
3.22
75
100
125
I
L
= 1mA
TEMPERATURE (
C)
50
ADJ PIN VOLTAGE (V)
25
1756 G08
25
0
50
1.230
1.225
1.220
1.215
1.210
1.205
1.200
1.195
1.190
75
100
125
I
L
= 1mA
INPUT VOLTAGE (V)
0
QUIESCENT CURRENT (mA)
40
35
30
25
20
15
10
5
0
8
1764 G09
2
4
6
10
7
1
3
5
9
T
J
= 25
C
R
L
=
V
SHDN
= V
IN
LT1764A-2.5 Quiescent Current
INPUT VOLTAGE (V)
0
QUIESCENT CURRENT (mA)
40
35
30
25
20
15
10
5
0
8
1764 G10
2
4
6
10
7
1
3
5
9
T
J
= 25
C
R
L
=
V
SHDN
= V
IN
TEMPERATURE (
C)
50
OUTPUT VOLTAGE (V)
1.53
25
1764A G40
1.50
1.48
25
0
50
1.47
1.46
1.54
1.52
1.51
1.49
75
100
125
I
L
= 1mA
LT1764A-2.5 Output Voltage
TEMPERATURE (
C)
50
OUTPUT VOLTAGE (V)
25
1756 G06
25
0
50
2.58
2.56
2.54
2.52
2.50
2.48
2.46
2.44
2.42
75
100
125
I
L
= 1mA
LT1764A-1.5 Output Voltage
LT1764A-1.5 Quiescent Current
INPUT VOLTAGE (V)
0
QUIESCENT CURRENT (mA)
40
35
30
25
20
15
10
5
0
8
1764 G41
2
4
6
10
7
1
3
5
9
T
J
= 25
C
R
L
=
V
SHDN
= V
IN
PDF 
ZIP