LT1111
Micropower
DC/DC Converter
Adjustable and Fixed 5V, 12V
FEATURES
s
s
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s
s
s
s
s
s
s
DESCRIPTIO
Operates at Supply Voltages from 2V to 30V
72kHz Oscillator
Works with Surface Mount Inductors
Only Three External Components Required
Step-Up or Step-Down Mode
Low-Battery Detector Comparator On-Chip
User Adjustable Current Limit
Internal 1A Power Switch
Fixed or Adjustable Output Voltage Versions
Space Saving 8-Pin MiniDIP or SO-8 Package
The LT1111 is a versatile micropower DC/DC converter.
The device requires only three external components to
deliver a fixed output of 5V or 12V. Supply voltage ranges
from 2V to 12V in step-up mode and to 30V in step-down
mode. The LT1111 functions equally well in step-up, step-
down, or inverting applications.
The LT1111 oscillator is set at 72kHz, optimizing the
device to work with off-the-shelf surface mount inductors.
The device can deliver 5V at 100mA from a 3V input in
step-up mode or 5V at 200mA from a 12V input in step-
down mode.
Switch current limit can be programmed with a single
resistor. An auxiliary open-collector gain block can be
configured as a low-battery detector, linear post regulator,
undervoltage lock-out circuit, or error amplifier.
For input sources of less than 2V use the LT1110.
APPLICATI
s
s
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s
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S
3V to 5V, 5V to 12V Converters
9V to 5V, 12V to 5V Converters
Remote Controls
Peripherals and Add-On Cards
Battery Backup Supplies
Uninterruptible Supplies
Laptop and Palmtop Computers
Cellular Telephones
Portable Instruments
Flash Memory VPP Generators
TYPICAL APPLICATI
Typical Load Regulation
6
5
OUTPUT VOLTAGE (V)
All Surface Mount 3V to 5V Step-Up Converter
SUMIDA
CD54-220M
MBRS120T3
22µH
3V INPUT
5V
100mA
4
3
2
1
0
0
25
V
IN
= 2V 2.2 2.4
I
LIM
+
V
IN
SW1
10
µ
F*
+
LT1111CS8-5
SENSE
GND
SW2
33
µ
F
*OPTIONAL
LT1111 • TA01
U
2.6
2.8 3V
50
75
100 125
150 175 200
LT1111 • TA02
UO
UO
LOAD CURRENT (mA)
1
LT11
11
ABSOLUTE
AXI U
RATI GS
Operating Temperature Range
LT1111C ............................................... 0°C to 70°C
LT1111I ......................................... – 40°C to 105°C
LT1111M ....................................... – 55°C to 125°C
Storage Temperature Range ................ – 65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
Supply Voltage (V
IN
) ............................................... 36V
SW1 Pin Voltage (V
SW1
) ......................................... 50V
SW2 Pin Voltage (V
SW2
) ............................ – 0.5V to V
IN
Feedback Pin Voltage (LT1111) ............................. 5.5V
Switch Current ....................................................... 1.5A
Maximum Power Dissipation ............................ 500mW
PACKAGE/ORDER I FOR ATIO
TOP VIEW
I
LIM
1
V
IN
2
SW1 3
SW2 4
J8 PACKAGE
8-LEAD CERAMIC DIP
8
7
6
5
FB (SENSE)*
SET
A0
GND
N8 PACKAGE
8-LEAD PLASTIC DIP
*FIXED VERSIONS
T
JMAX
= 150°C,
θ
JA
= 120°C/W (J)
T
JMAX
= 90°C,
θ
JA
= 130°C/W (N)
ORDER PART
NUMBER
LT1111CN8
LT1111CN8-5
LT1111CN8-12
LT1111MJ8
LT1111MJ8-5
LT1111MJ8-12
Consult factory for Industrial grade parts
ELECTRICAL CHARACTERISTICS
SYMBOL
I
Q
V
IN
PARAMETER
Quiescent Current
Input Voltage
Comparator Trip Point Voltage
V
OUT
Output Sense Voltage
Comparator Hysteresis
Output Hysteresis
f
OSC
DC
t
ON
V
SAT
Oscillator Frequency
Duty Cycle: Step-Up Mode
Step-Down Mode
Switch ON Time: Step-Up Mode
Step-Down Mode
SW Saturation Voltage, Step-Up Mode
SW Saturation Voltage, Step-Down Mode
I
FB
I
SET
V
OL
Feedback Pin Bias Current
Set Pin Bias Current
Gain Block Output Low
V
IN
= 3V, Military or Commercial Version
CONDITIONS
Switch OFF
Step-Up Mode
Step-Down Mode
LT1111 (Note 1)
LT1111-5 (Note 2)
LT1111-12 (Note 2)
LT1111
LT1111-5
LT1111-12
Full Load
I
LIM
Tied to V
IN
V
OUT
, = 5V, V
IN
= 12V
V
IN
= 3.0V, I
SW
= 650mA
V
IN
= 5.0V, I
SW
= 1A
V
IN
= 12V, I
SW
= 650mA
LT1111, V
FB
= 0V
V
SET
= V
REF
I
SINK
= 300µA, V
SET
= 1.00V
q
q
q
q
q
q
q
q
q
q
q
2
U
U
W
W W
U
W
TOP VIEW
I
LIM
1
V
IN
2
SW1 3
SW2 4
8
7
6
5
FB (SENSE)*
SET
A0
GND
ORDER PART
NUMBER
LT1111CS8
LT1111CS8-5
LT1111CS8-12
S8 PART MARKING
1111
11115
11111
S8 PACKAGE
8-LEAD PLASTIC SO
*FIXED VERSION
T
JMAX
= 90°C,
θ
JA
= 150°C/W
MIN
2.0
1.20
4.75
11.40
TYP
300
MAX
400
12.6
30.0
UNITS
µA
V
V
V
V
V
mV
mV
mV
kHz
%
%
µs
µs
V
V
V
nA
nA
V
1.25
5.00
12.00
8
32
75
1.30
5.25
12.60
12.5
50
120
88
59
50
9
7.8
0.65
1.0
1.5
120
300
0.4
54
43
24
5
3.3
72
50
34
7
5
0.5
0.8
1.1
70
70
0.15
LT1111
ELECTRICAL CHARACTERISTICS
SYMBOL
PARAMETER
Reference Line Regulation
A
V
I
LIM
Gain Block Gain
Current Limit
Current Limit Temperature Coefficient
Switch OFF Leakage Current
Maximum Excursion Below GND
V
IN
= 3V, Military or Commercial Version
CONDITIONS
5V
≤
V
IN
≤
30V
2V
≤
V
IN
≤
5V
R
L
= 100k (Note 3)
220Ω from I
LIM
to V
IN
q
q
q
MIN
TYP
0.02
0.20
MAX
0.075
0.400
UNITS
%/V
%/V
V/V
mA
%/
°C
1000
6000
400
– 0.3
1
– 400
10
– 350
Measured at SW1 Pin, V
SW1
= 12V
I
SW1
≤
10µA, Switch OFF
µA
mV
V
IN
= 3V, – 55°C
≤
T
A
≤
125°C unless otherwise noted.
SYMBOL
I
Q
f
OSC
DC
t
ON
PARAMETER
Quiescent Current
Oscillator Frequency
Duty Cycle: Step-Up Mode
Step-Down Mode
Switch ON Time: Step-Up Mode
Step-Down Mode
Reference Line Regulation
V
SAT
SW Saturation Voltage, Step-Up Mode
SW Saturation Voltage, Step-Down Mode
Full Load
I
LIM
Tied to V
IN
V
OUT
= 5V, V
IN
= 12V
2V
≤
V
IN
≤
5V, 25°C
≤
T
A
≤
125°C
2.4V
≤
V
IN
≤
5V, T
A
= – 55°C
0°C
≤
T
A
≤
125°C, I
SW
= 500mA,
T
A
= – 55°C, I
SW
= 400mA
V
IN
= 12V,
I
SW
= 500mA
0°C
≤
T
A
≤
125°C
T
A
= – 55°C
CONDITIONS
Switch OFF
q
q
q
q
q
q
MIN
45
40
20
5
3
LT1111M
TYP
300
72
50
7
0.2
0.5
MAX
500
100
62
55
11
9
0.4
0.8
0.65
1.5
2.0
UNITS
µA
kHz
%
%
µs
µs
%/V
%/V
V
V
V
V
IN
= 3V, 0°C
≤
T
A
≤
70°C unless otherwise noted.
SYMBOL
I
Q
f
OSC
DC
t
ON
PARAMETER
Quiescent Current
Oscillator Frequency
Duty Cycle: Step-Up Mode
Step-Down Mode
Switch ON Time: Step-Up Mode
Step-Down Mode
Reference Line Regulation
V
SAT
SW Saturation Voltage, Step-Up Mode
SW Saturation Voltage, Step-Down Mode
Full Load
I
LIM
Tied to V
IN
V
OUT
= 5V, V
IN
= 12V
2V
≤
V
IN
≤
5V
V
IN
= 3V, I
SW
= 650mA
V
IN
= 12V, I
SW
= 650mA
CONDITIONS
Switch OFF
q
q
q
q
q
q
q
q
q
MIN
300
54
43
24
5.0
3.3
LT1111C
TYP
72
50
34
7
5
0.2
0.5
1.1
MAX
450
95
59
50
9.0
7.8
0.7
0.65
1.50
UNITS
µA
kH
%
%
µs
µs
%/V
V
V
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
This specification guarantees that both the high and low trip points
of the comparator fall within the 1.20V to 1.30V range.
Note 2:
The output voltage waveform will exhibit a sawtooth shape due to
the comparator hysteresis. The output voltage on the fixed output versions
will always be within the specified range.
Note 3:
100k resistor connected between a 5V source and the A0 pin.
3
LT11
11
TYPICAL PERFOR A CE CHARACTERISTICS
Oscillator Frequency
100
75
74
73
OSCILLATOR FREQUENCY (KHz)
90
80
70
60
50
40
–50
FREQUENCY (KHz)
ON TIME (µs)
9 12 15 18 21 24 27 30
INPUT VOLTAGE (V)
LT1111 • TPC02
–25
25
75
0
50
TEMPERATURE (°C)
Duty Cycle
60
58
1.0
0.9
SATURATION VOLTAGE (V)
SATURATION VOLTAGE (V)
56
DUTY CYCLE (%)
54
52
50
48
46
44
42
40
–50
–25
50
75
0
25
TEMPERATURE (°C)
100
125
Switch ON Voltage
Step-Down Mode
2.00
1.75
V
IN
= 12V
I
SW =
650mA
1.4
1.2
1.0
OSCILLATOR FREQUENCY (KHz)
ON VOLTAGE (V)
ON VOLTAGE (V)
1.50
1.25
1.00
0.75
0.50
–50 –25
50
75
0
25
TEMPERATURE (°C)
4
U W
100
LT1111 • TPC01
LT1111 • TPC04
Oscillator Frequency
10
9.5
9.0
8.5
8.0
7.5
7.0
6.5
6.0
68
67
72
71
70
69
Switch ON Time
5.5
0
3
6
125
5.0
–50
–25
50
75
0
25
TEMPERATURE (°C)
100
125
LT111 • TPC03
Saturation Voltage
Step-Up Mode
1.4
V
IN
= 3V
I
SW =
650mA
Saturation Voltage
Step-Up Mode
V
IN
= 3V
1.2
1.0
0.8
0.6
0.4
0.2
0
0
0.2
0.4 0.6 0.8 1.0 1.2
SWITCH CURRENT (A)
1.4
1.6
V
IN
= 2V
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
–50
– 25
50
75
0
25
TEMPERATURE (°C)
100
125
V
IN
= 5V
LT1111 • TPC05
LT1111 • TPC06
Switch ON Voltage
Step-Down Mode
100
V
IN
= 12V
Minimum/Maximum Frequency
vs ON Time
90
0°C
≤
T
A
≤
70°C
80
70
60
50
–55°C
≤
T
A
≤
125°C
40
4
5
8
9
6
7
10
SWITCH ON TIME (µs)
11
12
0.8
0.6
0.4
0.2
0
100
125
0
0.2
0.8
0.4
0.6
SWITCH CURRENT (A)
1.0
LT1111 • TPC07
LT1111 • TPC08
LT1111 • TPC09
LT1111
TYPICAL PERFOR A CE CHARACTERISTICS
Quiescent Current
400
380
QUIESCENT CURRENT (µA)
QUIESCENT CURRENT (µA)
360
340
320
300
280
260
240
220
200
0
3
6
9 12 15 18 21 24 27 30
INPUT VOLTAGE (V)
LT1111 • TPC10
SWITCH CURRENT (A)
Set Pin Bias Current
100
90
80
BIAS CURRENT (nA)
60
50
40
30
20
10
0
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
BIAS CURRENT (nA)
70
PI FU CTI
S
GND (Pin 5):
Ground.
A0 (Pin 6):
Auxiliary Gain Block (GB) Output. Open collector,
can sink 300µA.
SET (Pin 7):
GB Input. GB is an op amp with positive input
connected to SET pin and negative input connected to
1.25V reference.
FB/SENSE (Pin 8):
On the LT1111 (adjustable) this pin
goes to the comparator input. On the LT1111-5 and
LT1111-12, this pin goes to the internal application resistor
that sets output voltage.
I
LIM
(Pin 1):
Connect this pin to V
IN
for normal use. Where
lower current limit is desired, connect a resistor between
I
LIM
and V
IN
. A 220Ω resistor will limit the switch current
to approximately 400mA.
V
IN
(Pin 2):
Input Supply Voltage.
SW1 (Pin 3):
Collector of Power Transistor. For step-up
mode connect to inductor/diode. For step-down mode
connect to V
IN
.
SW2 (Pin 4):
Emitter of Power Transistor. For step-up
mode connect to ground. For step-down mode connect to
inductor/diode. This pin must never be allowed to go more
than a Schottky diode drop below ground.
U W
Quiescent Current
500
450
400
350
300
250
200
150
100
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
Maximum Switch Current
vs R
LIM
STEP-UP
2V
≤
V
IN
≤
5V
STEP-DOWN
V
IN
= 12V
10
100
R
LIM
(Ω)
1000
LT1111 • TPC12
LT1111 • TPC11
Feedback Bias Current
100
90
80
70
60
50
40
30
20
10
0
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
LT1111 • TPC13
LT1111 • TPC14
UO
U
U
5
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