LT1575/LT1577
Ultrafast Transient Response,
Low Dropout Regulators
Adjustable and Fixed
FEATURES
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DESCRIPTION
The LT
®
1575/LT1577 are single/dual controller ICs that
drive low cost external N-channel MOSFETs as source
followers to produce ultrafast transient response, low
dropout voltage regulators.
The LT1575/LT1577 achieve unprecedented transient-
load performance by eliminating expensive tantalum or
bulk electrolytic output capacitors in the most demanding
modern microprocessor applications. Precision-trimmed
adjustable and fixed output voltage versions accommo-
date any required microprocessor power supply voltage.
Selection of the N-channel MOSFET R
DS(ON)
allows very
low dropout voltages to be achieved.
Unique protection features include a high side current
limit amplifier that activates a fault protection timer
circuit. A multifunction Shutdown pin provides either
current limit time-out with latchoff, overvoltage protec-
tion, thermal shutdown or a combination of these func-
tions. The LT1575 is available in 8-pin SO or PDIP and the
LT1577 is available in 16-pin narrow body SO.
, LTC and LT are registered trademarks of Linear Technology Corporation.
UltraFast is a trademark of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
PowerPC is a trademark of IBM Corporation.
s
s
s
UltraFast
TM
Transient Response
Eliminates
Tantalum and Electrolytic Output Capacitors
FET R
DS(ON)
Defines Dropout Voltage
1% Reference/Output Voltage Tolerance Over
Temperature
Typical Load Regulation: 1mV
High Side Sense Current Limit
Multifunction Shutdown Pin with Latchoff
APPLICATIONS
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s
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Pentium
®
Processor Supplies
PowerPC
TM
Supplies
5V to 3.XXV or 3.3V to 2.XXV Microprocessor Supplies
GTL Termination
Low Voltage Logic Supplies
Adjustable
1.5V Fixed
2.8V Fixed
3.3V Fixed
3.5V Fixed
5V Fixed
Adjustable, Adjustable
3.3V Fixed, Adjustable
3.3V Fixed, 2.8V Fixed
LT1575CN8/LT1575CS8
LT1575CN8-1.5/LT1575CS8-1.5
LT1575CN8-2.8/LT1575CS8-2.8
LT1575CN8-3.3/LT1575CS8-3.3
LT1575CN8-3.5/LT1575CS8-3.5
LT1575CN8-5/LT1575CS8-5
LT1577CS-ADJ/ADJ
LT1577CS-3.3/ADJ
LT1577CS-3.3/2.8
Consult factory for additional output voltage combinations available
in the LT1577.
TYPICAL APPLICATION
Ultrafast Transient Response 5V to 3.3V Low Dropout Regulator
(For Schematic Including Current Limit, See Typical Applications)
12V
1
* FOR T < 45°C:
C6 = 24
×
1µF Y5V
CERAMIC SURFACE
MOUNT CAPACITORS.
FOR T > 45°C:
C6 = 24
×
1µF X7R
CERAMIC SURFACE
MOUNT CAPACITORS.
PLACE C6 IN THE
MICROPROCESSOR
SOCKET CAVITY
2
LT1575-3.3
SHDN
IPOS
INEG
GATE
COMP
8
7
6
5
R2
5Ω
5V
C5
220µF
C2
V
IN
1µF 3
GND
4
OUT
+
Q1
IRFZ24
50mV/DIV
V
OUT
3.3V
5A
C6*
24µF
GND
1575/77 TA01
C3
10pF
R1
7.5k
C4
1000pF
2A/DIV
U
U
U
Transient Response for
0.2A to 5A Output Load Step
100µs/DIV
1575/77 TA02
1
LT1575/LT1577
ABSOLUTE
(Note 1)
AXI U
RATI GS
Junction Temperature (Note 2) ................ 0°C to 100°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
V
IN
, IPOS, INEG ...................................................... 22V
SHDN ....................................................................... V
IN
Operating Ambient Temperature Range ..... 0°C to 70°C
PACKAGE/ORDER I FOR ATIO
TOP VIEW
SHDN 1
V
IN
2
GND 3
FB 4
N8 PACKAGE
8-LEAD PDIP
8
7
6
5
IPOS
INEG
GATE
COMP
SHDN 1
V
IN
2
GND 3
OUT 4
S8 PACKAGE
8-LEAD PLASTIC SO
N8 PACKAGE
8-LEAD PDIP
T
JMAX
= 100°C,
θ
JA
= 100°C/ W (N8)
T
JMAX
= 100°C,
θ
JA
= 130°C/ W (S8)
T
JMAX
= 100°C,
θ
JA
= 100°C/ W (N8)
T
JMAX
= 100°C,
θ
JA
= 130°C/ W (S8)
ORDER PART NUMBER
LT1575CN8
LT1575CS8
ORDER PART NUMBER
LT1575CN8-1.5
LT1575CS8-1.5
LT1575CN8-2.8
LT1575CS8-2.8
LT1575CN8-3.3
LT1575CS8-3.3
LT1575CN8-3.5
LT1575CS8-3.5
LT1575CN8-5
LT1575CS8-5
S8 PART MARKING
1575
S8 PART MARKING
157515
157528
157533
157535
15755
TOP VIEW
SHDN1 1
V
IN1
2
GND1 3
OUT-3.3 4
SHDN2 5
V
IN2
6
GND2 7
FB 8
16 IPOS1
15 INEG1
14 GATE1
13 COMP1
12 IPOS2
11 INEG2
10 GATE2
9
COMP2
SHDN1 1
V
IN1
2
GND1 3
OUT-3.3 4
SHDN2 5
V
IN2
6
GND2 7
OUT-2.8 8
S PACKAGE
16-LEAD PLASTIC NARROW SO
T
JMAX
= 100°C,
θ
JA
= 100°C/ W
ORDER PART NUMBER
LT1577CS-3.3/ADJ
Consult factory for Industrial and Military grade parts.
2
U
U
W
W W
U
W
TOP VIEW
8
7
6
5
IPOS
INEG
GATE
COMP
SHDN1 1
V
IN1
2
GND1 3
FB1 4
SHDN2 5
V
IN2
6
GND2 7
FB2 8
TOP VIEW
16 IPOS1
15 INEG1
14 GATE1
13 COMP1
12 IPOS2
11 INEG2
10 GATE2
9
COMP2
S8 PACKAGE
8-LEAD PLASTIC SO
S PACKAGE
16-LEAD PLASTIC NARROW SO
T
JMAX
= 100°C,
θ
JA
= 100°C/ W
ORDER PART NUMBER
LT1577CS-ADJ/ADJ
TOP VIEW
16 IPOS1
15 INEG1
14 GATE1
13 COMP1
12 IPOS2
11 INEG2
10 GATE2
9
COMP2
S PACKAGE
16-LEAD PLASTIC NARROW SO
T
JMAX
= 100°C,
θ
JA
= 100°C/ W
ORDER PART NUMBER
LT1577CS-3.3/2.8
LT1575/LT1577
ELECTRICAL CHARACTERISTICS
T
A
= 25°C, V
IN
= 12V, GATE = 6V, IPOS = INEG = 5V, SHDN = 0.75V unless otherwise noted.
SYMBOL
I
Q
V
FB
V
OUT
PARAMETER
Supply Current
LT1575 Reference Voltage
q
CONDITIONS
q
MIN
5
– 0.6
– 1.0
– 0.6
– 1.0
– 0.6
– 1.0
– 0.6
– 1.0
– 0.6
– 1.0
– 0.6
– 1.0
TYP
12
1.210
1.210
1.500
1.500
2.800
2.800
3.300
3.300
3.500
3.500
5.000
5.000
0.01
– 0.6
MAX
19
0.6
1.0
0.6
1.0
0.6
1.0
0.6
1.0
0.6
1.0
0.6
1.0
0.03
– 4.0
1.5
UNITS
mA
%
%
%
%
%
%
%
%
%
%
%
%
%/V
µA
mA
dB
dB
dB
dB
dB
dB
LT1575-1.5 Output Voltage
q
LT1575-2.8 Output Voltage
q
LT1575-3.3 Output Voltage
q
LT1575-3.5 Output Voltage
q
LT1575-5 Output Voltage
q
Line Regulation
I
FB
I
OUT
A
VOL
FB Input Bias Current
OUT Divider Current
LT1575 Large-Signal Voltage Gain
LT1575-1.5 Large-Signal Voltage Gain
LT1575-2.8 Large-Signal Voltage Gain
LT1575-3.3 Large-Signal Voltage Gain
LT1575-3.5 Large-Signal Voltage Gain
LT1575-5 Large-Signal Voltage Gain
V
OL
V
OH
GATE Output Swing Low (Note 3)
GATE Output Swing High
IPOS + INEG Supply Current
Current Limit Threshold Voltage
10V
≤
V
IN
≤
20V
FB = V
FB
OUT = V
OUT
V
GATE
= 3V to 10V
V
GATE
= 3V to 10V
V
GATE
= 3V to 10V
V
GATE
= 3V to 10V
V
GATE
= 3V to 10V
V
GATE
= 3V to 10V
I
GATE
= 0mA
I
GATE
= 0mA
3V
≤
IPOS
≤
20V
q
q
q
q
q
q
q
q
q
q
q
q
q
0.5
69
67
60
60
60
56
V
IN
– 1.6
0.3
42
37
1.0
84
82
76
75
74
71
2.5
V
IN
– 1
0.625
50
50
– 0.20
3.0
1.0
58
63
– 0.50
8.0
– 23
0.25
2.20
1.240
150
V
V
mA
mV
mV
%/V
µA
µA
V
V
V
mV
Current Limit Threshold Voltage
Line Regulation
SHDN Sink Current
SHDN Source Current
SHDN Low Clamp Voltage
SHDN High Clamp Voltage
SHDN Threshold Voltage
SHDN Threshold Hysteresis
3V
≤
IPOS
≤
20V
Current Flows Into Pin
Current Flows Out of Pin
q
q
q
q
q
q
q
2.5
–8
1.50
1.18
50
5.0
– 15
0.1
1.85
1.21
100
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
Absolute Maximum Ratings are those values beyond which the life
of the device may be impaired.
Note 2:
T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LT1575CN8: T
J
= T
A
+ (P
D
• 100°CW)
LT1575CS8: T
J
= T
A
+ (P
D
• 130°CW)
LT1577CS: T
J
= T
A
+ (P
D
• 100°CW)
Because the LT1577 consists of two regulators in the package, the total
LT1577 power dissipation must be used for its junction temperature
calculation. The total LT1577 P
D
= P
D
(Regulator 1) + P
D
(Regulator 2).
Note 3:
The V
GS(th)
of the external MOSFET must be greater than
3V – V
OUT
.
3
LT1575/LT1577
TYPICAL PERFORMANCE CHARACTERISTICS
Quiescent Current vs Temperature
19
18
17
16
15
V
IN
= 12V
14
V
IN
= 20V
13
12
V
IN
= 8V
11
10
9
8
7
6
5
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G01
FB INPUT BIAS CURRENT (µA)
QUIESCENT CURRENT (mA)
REFERENCE VOLTAGE (V)
LT1575-1.5 V
OUT
vs Temperature
1.515
1.512
REFERENCE VOLTAGE (V)
1.509
1.506
1.503
1.500
1.497
1.494
1.491
1.488
1.485
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G04
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
LT1575-3.5 V
OUT
vs Temperature
3.535
3.530
3.525
3.520
3.515
3.510
3.505
3.500
3.495
3.490
3.485
3.480
3.475
3.470
3.465
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G07
OUT DIVIDER CURRENT (mA)
OUTPUT VOLTAGE (V)
OUTPUT VOLTAGE (V)
4
U W
Adjustable LT1575 V
REF
vs Temperature
1.222
1.220
1.218
1.216
1.214
1.212
1.210
1.208
1.206
1.204
1.202
1.200
1.198
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G02
FB Input Bias Current
vs Temperature
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
V
IN
= 20V
V
IN
= 12V
V
IN
= 8V
0
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G03
LT1575-2.8 V
OUT
vs Temperature
2.828
2.824
2.800
2.816
2.812
2.808
2.804
2.800
2.796
2.792
2.788
2.784
2.780
2.776
2.772
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G05
LT1575-3.3 V
OUT
vs Temperature
3.333
3.327
3.321
3.315
3.309
3.303
3.297
3.291
3.285
3.279
3.273
3.267
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G06
LT1575-5 V
OUT
vs Temperature
5.050
5.040
5.030
5.020
5.010
5.000
4.990
4.980
4.970
4.960
4.950
–75 –50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G08
OUT Divider Current
vs Temperature
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G09
LT1575/LT1577
TYPICAL PERFORMANCE CHARACTERISTICS
V
REF
/V
OUT
Line Regulation
vs Temperature
0.030
0.025
LARGE-SIGNAL VOLTAGE GAIN (dB)
120
115
110
105
100
95
90
85
80
75
70
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G11
ERROR AMPLIFIER GAIN AND PHASE
LINE REGULATION (%/V)
0.020
0.015
0.010
0.005
0
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G10
Gate Output Swing Low
vs Temperature
3.00
2.75
I
LOAD
= 50mA
GATE OUTPUT SWING HIGH (V)
GATE OUTPUT SWING LOW (V)
2.5
2.0
1.5
1.0
NO LOAD
0.5
0
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G14
2.50
NO LOAD
2.25
2.00
1.75
1.50
1.25
1.00
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G13
I
POS
+ I
NEG
SUPPLY CURRENT (µA)
Current Limit Threshold Voltage
vs Temperature
CURRENT LIMIT THRESHOLD VOLTAGE (mV)
65
60
55
50
IPOS = 20V
45
40
35
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G16
CURRENT LIMIT THRESHOLD
VOLTAGE LINE REGULATION (%/V)
U W
Error Amplifier Large-Signal
Voltage Gain vs Temperature
200
Gain and Phase vs Frequency
150
PHASE
100
GAIN
50
0
1k
10k
100k
1M
FREQUENCY (Hz)
10M
100M
1575/77 G12
Gate Output Swing High
vs Temperature
3.0
1000
900
800
700
600
500
400
IPOS + INEG Supply Current
vs Temperature
I
LOAD
= 50mA
IPOS = INEG = 5V
IPOS = INEG = 12V
IPOS = INEG = 20V
IPOS = INEG = 3V
300
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G15
Current Limit Threshold Voltage
Line Regulation vs Temperature
0
– 0.1
IPOS = 5V
IPOS = 3V
– 0.2
– 0.3
– 0.4
– 0.5
–75 – 50 –25 0 25 50 75 100 125 150 175
TEMPERATURE (°C)
1575/77 G17
5
