LT1764 Series
3A, Fast Transient
Response, Low Noise,
LDO Regulators
FEATURES
s
s
s
s
s
s
s
s
s
s
s
s
s
s
s
DESCRIPTIO
Optimized for Fast Transient Response
Output Current: 3A
Dropout Voltage: 340mV at 3A
Low Noise: 40
µ
V
RMS
(10Hz to 100kHz)
1mA Quiescent Current
Wide Input Voltage Range: 2.7V to 20V
No Protection Diodes Needed
Controlled Quiescent Current in Dropout
Fixed Output Voltages: 1.5V, 1.8V, 2.5V, 3.3V
Adjustable Output from 1.21V to 20V
< 1µA Quiescent Current in Shutdown
Stable with 10µF Output Capacitor
Reverse Battery Protection
No Reverse Current
Thermal Limiting
APPLICATIO S
s
s
The LT
®
1764 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. Oper-
ating quiescent current is 1mA, dropping to < 1µA 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 LT1764 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 LT1764
regulators are stable with output capacitors as low as 10µF.
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 LT1764 regu-
lators are available in 5-lead TO-220 and DD packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
3.3V to 2.5V Logic Power Supply
Post Regulator for Switching Supplies
TYPICAL APPLICATIO
400
3.3V
IN
to 2.5V
OUT
Regulator
DROPOUT VOLTAGE (mV)
350
300
250
200
150
100
50
0
0
0.5
1.0
1.5
2.0
LOAD CURRENT (A)
2.5
3.0
1764 TA02
+
V
IN
> 3V
10µF
IN
OUT
LT1764-2.5
+
10µF
2.5V
3A
SHDN SENSE
GND
1764 TA01
U
Dropout Voltage
1764fa
U
U
1
LT1764 Series
ABSOLUTE
MAXIMUM
RATINGS
(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
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
PACKAGE/ORDER INFORMATION
FRONT VIEW
5
4
TAB IS
GND
3
2
1
Q PACKAGE
5-LEAD PLASTIC DD
SENSE/ADJ*
OUT
GND
IN
SHDN
ORDER PART
NUMBER
LT1764EQ
LT1764EQ-1.5
LT1764EQ-1.8
LT1764EQ-2.5
LT1764EQ-3.3
TAB IS
GND
*PIN 5 = SENSE FOR LT1764-1.8/
LT1764-2.5/LT1764-3.3
= ADJ FOR LT1764
T
JMAX
= 150°C,
θ
JA
= 30°C/ W
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C. (Note 2)
PARAMETER
Minimum Input Voltage
(Notes 3, 11)
CONDITIONS
I
LOAD
= 0.5A
I
LOAD
= 1.5A
I
LOAD
= 2.7A, 110°C < T
J
≤
125°C
I
LOAD
= 3A, – 40°C
≤
T
J
≤
110°C
LT1764-1.5 V
IN
= 2.21V, I
LOAD
= 1mA
2.7V < V
IN
< 20V, 1mA < I
LOAD
< 3A, – 40°C
≤
T
J
≤
110°C
2.7V < V
IN
< 20V, 1mA < I
LOAD
< 2.7A, 110°C < T
J
≤
125°C
LT1764-1.8 V
IN
= 2.3V, I
LOAD
= 1mA
2.8V < V
IN
< 20V, 1mA < I
LOAD
< 3A, – 40°C
≤
T
J
≤
110°C
2.8V < V
IN
< 20V, 1mA < I
LOAD
< 2.7A, 110°C < T
J
≤
125°C
LT1764-2.5 V
IN
= 3V, I
LOAD
= 1mA
3.5V < V
IN
< 20V, 1mA < I
LOAD
< 3A, – 40°C
≤
T
J
≤
110°C
3.5V < V
IN
< 20V, 1mA < I
LOAD
< 2.7A, 110°C < T
J
≤
125°C
LT1764-3.3 V
IN
= 3.8V, I
LOAD
= 1mA
4.3V < V
IN
< 20V, 1mA < I
LOAD
< 3A, – 40°C
≤
T
J
≤
110°C
4.3V < V
IN
< 20V, 1mA < I
LOAD
< 2.7A, 110°C < T
J
≤
125°C
ADJ Pin Voltage
(Notes 3, 4)
LT1764
V
IN
= 2.21V, I
LOAD
= 1mA
2.7V < V
IN
< 20V, 1mA < I
LOAD
< 3A, – 40°C
≤
T
J
≤
110°C
2.7V < V
IN
< 20V, 1mA < I
LOAD
< 2.7A, 110°C < T
J
≤
125°C
1.477
1.447
1.447
1.773
1.737
1.737
2.462
2.412
2.412
3.250
3.183
3.183
1.192
1.168
1.168
MIN
TYP
1.7
1.9
2.3
2.3
1.500
1.500
1.500
1.800
1.800
1.800
2.500
2.500
2.500
3.300
3.300
3.300
1.210
1.210
1.210
MAX
UNITS
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
V
Regulated Output Voltage
(Note 4)
2
U
U
W
W W
U
W
FRONT VIEW
5
4
3
2
1
T PACKAGE
5-LEAD PLASTIC TO-220
GND
IN
SHDN
SENSE/ADJ*
OUT
ORDER PART
NUMBER
LT1764ET
LT1764ET-1.5
LT1764ET-1.8
LT1764ET-2.5
LT1764ET-3.3
*PIN 5 = SENSE FOR LT1764-1.8/
LT1764-2.5/LT1764-3.3
= ADJ FOR LT1764
T
JMAX
= 150°C,
θ
JA
= 50°C/ W
2.7
2.7
1.523
1.545
1.545
1.827
1.854
1.854
2.538
2.575
2.575
3.350
3.400
3.400
1.228
1.246
1.246
1764fa
LT1764 Series
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C. (Note 2)
PARAMETER
Line Regulation
CONDITIONS
LT1764-1.5
LT1764-1.8
LT1764-2.5
LT1764-3.3
LT1764 (Note 3)
LT1764-1.5
∆V
IN
= 2.21V to 20V, I
LOAD
= 1mA
∆V
IN
= 2.3V to 20V, I
LOAD
= 1mA
∆V
IN
= 3V to 20V, I
LOAD
= 1mA
∆V
IN
= 3.8V to 20V, I
LOAD
= 1mA
∆V
IN
= 2.21V to 20V, I
LOAD
= 1mA
V
IN
= 2.7V,
∆I
LOAD
= 1mA to 3A
V
IN
= 2.7V,
∆I
LOAD
= 1mA to 3A, – 40°C
≤
T
J
≤
110°C
V
IN
= 2.7V,
∆I
LOAD
= 1mA to 2.7A, 110°C < T
J
≤
125°C
V
IN
= 2.8V,
∆I
LOAD
= 1mA to 3A
V
IN
= 2.8V,
∆I
LOAD
= 1mA to 3A, – 40°C
≤
T
J
≤
110°C
V
IN
= 2.8V,
∆I
LOAD
= 1mA to 2.7A, 110°C < T
J
≤
125°C
V
IN
= 3.5V,
∆I
LOAD
= 1mA to 3A
V
IN
= 3.5V,
∆I
LOAD
= 1mA to 3A, – 40°C
≤
T
J
≤
110°C
V
IN
= 3.5V,
∆I
LOAD
= 1mA to 2.7A, 110°C < T
J
≤
125°C
V
IN
= 4.3V,
∆I
LOAD
= 1mA to 3A
V
IN
= 4.3V,
∆I
LOAD
= 1mA to 3A, – 40°C
≤
T
J
≤
110°C
V
IN
= 4.3V,
∆I
LOAD
= 1mA to 2.7A, 110°C < T
J
≤
125°C
q
q
q
q
q
MIN
TYP
2.5
3
4
4.5
2
3
MAX
10
10
10
10
10
7
23
23
8
25
25
10
30
30
12
40
40
5
20
20
0.05
0.10
0.13
0.18
0.20
0.27
0.33
0.40
0.66
0.45
0.66
1.5
1.6
5
18
75
200
200
10
2
1
30
1
UNITS
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
mV
V
V
V
V
V
V
V
V
V
V
V
mA
mA
mA
mA
mA
mA
mA
µV
RMS
µA
V
V
µA
µA
µA
dB
Load Regulation
LT1764-1.8
4
LT1764-2.5
4
LT1764-3.3
4
LT1764 (Note 3) V
IN
= 2.7V,
∆I
LOAD
= 1mA to 3A
V
IN
= 2.7V,
∆I
LOAD
= 1mA to 3A, – 40°C
≤
T
J
≤
110°C
V
IN
= 2.7V,
∆I
LOAD
= 1mA to 2.7A, 110°C < T
J
≤
125°C
Dropout Voltage
V
IN
= V
OUT(NOMINAL)
(Notes 5, 6, 11)
I
LOAD
= 1mA
I
LOAD
= 1mA
I
LOAD
= 100mA
I
LOAD
= 100mA
I
LOAD
= 500mA
I
LOAD
= 500mA
I
LOAD
= 1.5A
I
LOAD
= 1.5A
I
LOAD
= 2.7A, 110°C < T
J
≤
125°C
I
LOAD
= 3A
I
LOAD
= 3A, – 40°C
≤
T
J
≤
110°C
GND Pin Current
V
IN
= V
OUT(NOMINAL)
+ 1V
(Notes 5, 7)
I
LOAD
= 0mA
I
LOAD
= 1mA
I
LOAD
= 100mA
I
LOAD
= 500mA
I
LOAD
= 1.5A
I
LOAD
= 2.7A, 110°C < T
J
≤
125°C
I
LOAD
= 3A, – 40°C
≤
T
J
≤
110°C
C
OUT
= 10µF, I
LOAD
= 3A, BW = 10Hz to 100kHz
(Notes 3, 8)
V
OUT
= Off to On
V
OUT
= On to Off
V
SHDN
= 0V
V
SHDN
= 20V
V
IN
= 6V, V
SHDN
= 0V
V
IN
– V
OUT
= 1.5V (Avg), V
RIPPLE
= 0.5V
P-P
,
f
RIPPLE
= 120Hz, I
LOAD
= 1.5A
55
q
q
q
q
q
q
q
q
2
0.02
0.07
q
0.14
q
0.25
q
0.34
1
1.1
3.5
11
40
120
120
40
3
0.25
0.9
0.75
0.01
7
0.01
63
Output Voltage Noise
ADJ Pin Bias Current
Shutdown Threshold
SHDN Pin Current
(Note 9)
Quiescent Current in Shutdown
Ripple Rejection
1764fa
3
LT1764 Series
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25°C. (Note 2)
PARAMETER
Current Limit
CONDITIONS
V
IN
= 7V, V
OUT
= 0V
LT1764-1.8, LT1764-2.5, LT1764-3.3
V
IN
= V
OUT(NOMINAL)
+ 1V,
∆V
OUT
= – 0.1V, – 40°C
≤
T
J
≤
110°C
V
IN
= V
OUT(NOMINAL)
+ 1V,
∆V
OUT
= – 0.1V, 110°C < T
J
≤
125°C
LT1764, LT1764-1.5
V
IN
= 2.7V,
∆V
OUT
= – 0.1V, – 40°C
≤
T
J
≤
110°C
V
IN
= 2.7V,
∆V
OUT
= – 0.1V, 110°C < T
J
≤
125°C
Input Reverse Leakage Current
V
IN
= – 20V, V
OUT
= 0V
q
MIN
TYP
4
MAX
UNITS
A
A
A
A
A
3.1
2.8
3.1
2.8
1
600
600
600
600
300
1200
1200
1200
1200
600
mA
µA
µA
µA
µA
µA
Reverse Output Current (Note 10) LT1764-1.5 V
OUT
= 1.5V, V
IN
< 1.5V
LT1764-1.8 V
OUT
= 1.8V, V
IN
< 1.8V
LT1764-2.5 V
OUT
= 2.5V, V
IN
< 2.5V
LT1764-3.3 V
OUT
= 3.3V, V
IN
< 3.3V
LT1764 (Note 3) V
OUT
= 1.21V, V
IN
< 1.21V
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2:
The LT1764 regulators are tested and specified under pulse load
conditions such that T
J
≈
T
A
. The LT1764 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 LT1764 (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 LT1764
(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 300µA 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 LT1764, LT1764-1.5 and LT1764-1.8 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.
TYPICAL PERFOR A CE CHARACTERISTICS
Typical Dropout Voltage
600
GUARANTEED DROPOUT VOLTAGE (mV)
500
DROPOUT VOLTAGE (mV)
400
T
J
= 125°C
300
200
T
J
= 25°C
100
0
500
T
J
≤
125°C
400
300
T
J
≤
25°C
200
100
0
0
0.5
DROPOUT VOLTAGE (mV)
0
0.5
1.0
1.5
2.0
OUTPUT CURRENT (A)
4
U W
2.5
1764 G01
Guaranteed Dropout Voltage
700
600
= TEST POINTS
600
500
400
Dropout Voltage
I
L
= 3A
300
I
L
= 1.5A
200
I
L
= 0.5A
100
0
–50 –25
I
L
= 100mA
I
L
= 1mA
3.0
2.0
1.5
1.0
OUTPUT CURRENT (A)
2.5
3.0
1764 G02
50
25
75
0
TEMPERATURE (°C)
100
125
1764 G03
1764fa
LT1764 Series
TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current
1.4
1.2
QUIESCENT CURRENT (mA)
LT1764-1.8/2.5/3.3
1.0
LT1764
0.8
0.6
0.4
0.2
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
0
–50 –25
V
IN
= 6V
R
L
=
∞
I
L
= 0
V
SHDN
= V
IN
50
25
75
0
TEMPERATURE (°C)
100
125
LT1764-3.3 Output Voltage
3.38
3.36
OUTPUT VOLTAGE (V)
I
L
= 1mA
QUIESCENT CURRENT (mA)
ADJ PIN VOLTAGE (V)
3.34
3.32
3.30
3.28
3.26
3.24
3.22
– 50 – 25
0
75
50
25
TEMPERATURE (°C)
100
125
LT1764-2.5 Quiescent Current
40
35
T
J
= 25°C
R
L
=
∞
V
SHDN
= V
IN
40
35
QUIESCENT CURRENT (mA)
QUIESCENT CURRENT (mA)
30
25
20
15
10
5
0
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
30
25
20
15
10
5
0
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
QUIESCENT CURRENT (mA)
U W
1764 G04
1756 G07
1764 G10
LT1764-1.8 Output Voltage
1.84
1.83
1.82
1.81
1.80
1.79
1.78
1.77
1.76
– 50 – 25
0
75
50
25
TEMPERATURE (°C)
100
125
I
L
= 1mA
2.58
2.56
2.54
2.52
2.50
2.48
2.46
2.44
LT1764-2.5 Output Voltage
I
L
= 1mA
2.42
– 50 – 25
0
75
50
25
TEMPERATURE (°C)
100
125
1756 G05
1756 G06
LT1764 ADJ Pin Voltage
1.230
1.225
1.220
1.215
1.210
1.205
1.200
1.195
1.190
– 50 – 25
0
75
50
25
TEMPERATURE (°C)
100
125
LT1764-1.8 Quiescent Current
40
35
30
25
20
15
10
5
0
0
1
2
3 4 5 6 7
INPUT VOLTAGE (V)
8
9
10
T
J
= 25°C
R
L
=
∞
V
SHDN
= V
IN
I
L
= 1mA
1756 G08
1764 G09
LT1764-3.3 Quiescent Current
1.6
T
J
= 25°C
R
L
=
∞
V
SHDN
= V
IN
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
LT1764 Quiescent Current
T
J
= 25°C
R
L
= 4.3k
V
SHDN
= V
IN
0
2
4
6 8 10 12 14 16 18 20
INPUT VOLTAGE (V)
1764 G12
1764 G11
1764fa
5
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