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OBSOLETE:
LT1500/LT1501
Adaptive-Frequency
Current Mode
Switching Regulators
DESCRIPTION
The LT
®
1500 is an adaptive-frequency current mode step-
up switching regulator with an internal power switch that
is rated up to 700mA. In contrast to pulse skipping
switching regulators, the LT1500 uses a current mode
topology that provides lower noise operation and im-
proved efficiency. Only at very light loads is Burst Mode
TM
activated to give high efficiency and micropower opera-
tion. High switching frequency (up to 500kHz) allows very
small inductors to be used, along with ceramic capacitors
if desired.
The LT1500 operates with input voltages from 1.8V to 15V
and has only 200µA operating current dropping to 8µA in
shutdown. A low-battery comparator is included which
stays alive in shutdown. A second output feedback pin
with negative polarity allows negative output voltages to
be regulated when the switcher is connected up as a Cuk
or a flyback converter.
Two package types are available. The LT1500 comes in a
14-pin SO package, with two options available for fixed
output (3.3V or 5V) or adjustable operation. A reduced
feature part, the LT1501, comes in the smaller 8-pin SO
package with internal frequency compensation. It is also
available in adjustable and fixed output voltage versions.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
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Low Noise Adaptive-Frequency Current Mode
Operation Avoids Low Frequency Noise at
Most Load Currents
Can Be Externally Synchronized (LT1500)
Micropower Quiescent Current: 200µA
Shutdown Current: 8µA Typ
Internal Loop Compensation
Low-Battery Comparator Active in Shutdown
Minimum Input Voltage: 1.8V Typ
Additional Negative Voltage Feedback Pin (LT1500)
Up to 500kHz Switching Frequency
Uses Low Profile, Low Cost Surface Mount Inductors
APPLICATIONS
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Portable Instrumentation
Battery Operated Systems
PDA’s
Standby Power
TYPICAL APPLICATION
U
2-Cell to 5V Converter
D1
MBR0520L
22µH
†
2 EACH
NiCd OR
ALKALINE
CELLS
301k
1%
V
IN
SHDN
I
SENSE
SW
+
33µF*
6V
301k
1%
LT1501-5
LBI
LBO
1nF
OUT
GND
+
220µF**
10V
TANT
* AVX, TPSC107M006R0150
** AVX, TPSD107M010 R0100
†
SUMIDA CD73-220, CD54-220
OR CD43-220. SELECT ACCORDING
TO MAXIMUM LOAD CURRENT
LT1500/01 • TA01
LOW-BATTERY FLAG
(USE EXTERNAL PULL-UP)
U
FEATURES
U
5V, 200mA
1
LT1500/LT1501
ABSOLUTE
MAXIMUM
RATINGS
Supply Voltage ........................................................ 20V
Switch Voltage (SW) ............................................... 30V
Shutdown Voltage (SHDN) ...................................... 20V
I
SENSE
Voltage.......................................................... 20V
FB Voltage ................................................................. 5V
LBI Voltage ................................................................ 5V
LBO Voltage ............................................................. 15V
Operating Ambient Temperature Range
Commercial ............................................. 0°C to 70°C
Industrial ............................................ – 40°C to 85°C
Operating Junction Temperature Range
Commercial ........................................... 0°C to 100°C
Industrial .......................................... – 40°C to 100°C
Storage Temperature Range ................. – 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................. 300°C
PACKAGE/ORDER INFORMATION
TOP VIEW
SHDN 1
V
C
2
V
IN
3
I
SENSE
4
NC 5
GND 6
PGND 7
14 FB
13 NFB
12 SS
11 LBI
10 LBO
9
8
SYNC
SW
SHDN 1
V
C
2
V
IN
3
I
SENSE
4
NC 5
GND 6
PGND 7
TOP VIEW
14 V
OUT
(3.3V/5V)
13 SELECT
12 SS
11 LBI
10 LBO
9
8
SYNC
SW
SHDN 1
V
IN
2
I
SENSE
3
GND 4
TOP VIEW
8
7
6
5
FB/OUT
LBI
LBO
SW
S PACKAGE
14-LEAD PLASTIC SO
T
JMAX
= 100°C,
θ
JA
= 100°C/ W
S PACKAGE
14-LEAD PLASTIC SO
T
JMAX
= 100°C,
θ
JA
= 100°C/ W
ORDER PART NUMBER
LT1500CS
LT1500IS
ORDER PART NUMBER
LT1500CS-3/5
LT1500IS-3/5
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
PARAMETER
Feedback/Output Pin Reference Voltage
CONDITIONS
T
J
= 25°C, V
IN
= 2.3V unless otherwise noted.
MIN
q
q
q
q
q
LT1500/LT1501, T
J
= 25°C
All Conditions (Note 6)
LT1500-3/5, Select Pin Open
All Conditions (Note 6)
LT1500-3/5, Select Pin Grounded
All Conditions (Note 6)
Reference Voltage Line Regulation
Feedback Pin Bias Current
V
IN
= 2.3V to 15V
2
U
U
W
W W
U
W
S8 PACKAGE
8-LEAD PLASTIC SO
T
JMAX
= 100°C,
θ
JA
= 120°C/ W
ORDER PART NUMBER
LT1501CS8
LT1501CS8-3.3
LT1501CS8-5
LT1501IS8
LT1501IS8-3.3
LT1501IS8-5
TYP
1.265
3.300
5.000
0.02
30
MAX
1.290
1.295
3.370
3.400
5.100
5.15
0.06
100
UNITS
V
V
V
V
V
V
%/V
nA
1.240
1.235
3.230
3.200
4.900
4.85
LT1500/LT1501
ELECTRICAL CHARACTERISTICS
PARAMETER
Internal Divider Current
Operating Quiescent Current
Supply Current in Shutdown
CONDITIONS
T
J
= 25°C, V
IN
= 2.3V unless otherwise noted.
MIN
q
q
q
q
q
q
TYP
22
33
200
MAX
30
45
280
320
15
20
1.1
UNITS
µA
µA
µA
µA
µA
µA
V
µA
V
V
V
V
Ω
A
V
µA
µA
ns
ns
Ω
LT1500-3.3/LT1501-3.3
LT1500-5/LT1501-5
V
IN
≤
5V, V
SHDN
= 2.3V (Note 1)
V
IN
= 15V
V
SHDN
≤
0.2V, Fixed Voltages (Note 7)
T
J
≥
0°C
T
J
< 0°C
8
0.4
3
2.0
1.8
2.0
Shutdown Pin Threshold
Shutdown Pin Input Current
Input Start-Up Voltage
V
SHDN
= 2.3V
V
SHDN
= V
IN
T
J
≥
0°C
T
J
< 0°C
Light Load
Full Load
q
q
10
2.1
2.2
2.1
Undervoltage Lockout
Power Switch
Switch On Resistance
Peak Switch Current (Note 3)
Switch Breakdown Voltage
Switch Leakage Current
Switch Turn-On Delay (Note 5)
Switch Turn-Off Delay (Note 5)
Current Sense Resistor
Low-Battery Comparator
Low-Battery Threshold
Threshold Hysteresis
LBI Input Bias Current
LBO Output Low State
LBO Leakage Current
LT1500 Functions
SYNC Pin Bias Current
SYNC Pin Threshold
Error Amplifier Transconductance
V
C
Pin Source Current
V
C
Pin High Clamp Voltage
NFB Reference Voltage
NFB Pin Bias Current
NFB to FB Transconductance
Soft Start Bias Current
I
SW
= 0.7A (Note 2)
q
q
0.50
0.7
30
0.85
45
0.2
0.3
800
400
0.72
1.3
I
SW
= 100µA
V
SW
= 5V
V
SW
= 20V
q
q
q
5
10
q
0.28
0.42
Falling Edge
q
1.20
1.24
20
1.28
V
mV
q
20
0.1
0.3
50
0.25
0.5
2
nA
V
V
µA
µA
V
µmho
µA
V
LBI
= 1.2V, I
SINK
= 100µA
I
SINK
= 2mA
V
LBI
= 1.3V, V
LBO
≤
15V
q
q
q
V
SYNC
= 3.3V
q
q
15
0.4
600
20
1.20
1.26
1.265
12
10,000
35
1.3
1.32
1.300
20
V
V
µA
µmho
µA
FB Pin Open
q
q
1.230
Note 4
Current Flows Out of Pin
q
2
4
7
3
LT1500/LT1501
ELECTRICAL CHARACTERISTICS
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1:
Feedback pin or output is held sightly above the regulated value to
force the V
C
node low and switching to stop.
Note 2:
See Typical Performance Characteristics for graph of Guaranteed
Switch Voltage vs Saturation Voltage.
Note 3:
Peak switch current is the guaranteed minimum value of switch
current available in normal operation. Highest calculated switch current at
full load should not exceed the minimum value shown.
Note 4:
Loading on FB pin will affect NFB reference voltage.
∆V
NFB
= I
FB
/gm.
Do not exceed 10µA loading on FB when NFB is being used.
Note 5:
This is the delay between sense pin current reaching its upper or
lower threshold and switch transition. Switch delay times cause peak-to-
peak inductor current to increase and therefore switching frequency to be
low. This effect will be significant for frequencies above 100kHz. See
Application Information and Typical Performance Characteristics.
Note 6:
Reference voltage under all conditions includes V
IN
= 2.1V to 15V,
all loads and full temperature range.
Note 7:
As with all boost regulators the output voltage of the LT1500
cannot fall to less than input voltage because of the path through the catch
diode. This means that the output voltage divider on adjustable parts will
still be generating feedback voltage at the FB pin (fixed voltage parts have
an internal switch to disconnect the divider in shutdown). If the voltage on
FB is greater than 0.6V in shutdown, the internal error amplifier will draw
current that adds to shutdown current. See graph of Shutdown Current vs
FB voltage in Typical Performance Characteristics.
TYPICAL PERFORMANCE CHARACTERISTICS
Switching Frequency
(3.3V Output)
1000
VIN = 2.3V
10µH
FREQUENCY (kHz)
FREQUENCY (kHz)
FREQUENCY (kHz)
20µH
100
50µH
100µH
1000
20µH
100
50µH
100µH
BURST REGION
10
0
50
150
200
100
LOAD CURRENT (mA)
250
300
LTC1500/01 • TPC20
Efficiency (3.3V Output)
100
90
80
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
30
1
10
100
LOAD CURRENT (mA)
1000
LTC1500/01 • TPC17
L = 100µH
L = 10µH
L = 33µH
70
60
50
L = 10µH
L = 33µH
EFFICIENCY (%)
T
J
= 25°C
V
IN
= 2.3V
LOW LOSS INDUCTOR
4
U W
Switching Frequency (5V Output)
VIN = 3V
10µH
Switching Frequency (12V Output)
1000
10µH
20µH
50µH
100µH
100
VIN = 5V
BURST REGION
10
0
50
100
150
200
LOAD CURRENT (mA)
250
300
BURST REGION
10
0
25
50 75 100 125 150 175
LOAD CURRENT (mA)
200
LTC1500/01 • TPC21
LTC1500/01 • TPC22
Efficiency (5V Output)
100
90
80
L = 100µH
100
90
80
70
60
50
V
IN
= 3V
LOW LOSS INDUCTOR
1
10
100
LOAD CURRENT (mA)
1000
LTC1500/01 • TPC18
Efficiency (12V Output)
L = 100µH
L = 33µH
L = 10µH
40
30
40
30
1
V
IN
= 5V
LOW LOSS INDUCTOR
10
100
LOAD CURRENT (mA)
1000
LTC1500/01 • TPC19
LT1500/LT1501
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency (3.3V Output)
100
90
EFFICIENCY (%)
80
70
60
50
T
J
= 25°C
L = 33µH
LOW LOSS INDUCTOR
2.00
2.25 2.50 2.75
INPUT VOLTAGE (V)
3.00
3.25
100
90
EFFICIENCY (%)
I
LOAD
= 10mA
80
70
60
50
40
2.0
2.5
3.0
3.5
4.0
INPUT VOLTAGE (V)
4.5
5.0
T
J
= 25°C
L = 33µH
LOW LOSS INDUCTOR
I
LOAD
= 10mA
I
LOAD
= 100mA
EFFICIENCY (%)
I
LOAD
= 100mA
40
1.75
Inductor Copper Loss
(3.3V Output)
10
R = 1Ω
R = 0.5Ω
10
EFFICIENCY LOSS (%)
R = 0.2Ω
EFFICIENCY LOSS (%)
R = 0.2Ω
R = 0.1Ω
EFFICIENCY LOSS (%)
1
R = 0.1Ω
V
IN
= 2.3V
0.1
0
50
100
150
200
LOAD CURRENT (mA)
250
300
0.1
0
50
100
150
200
LOAD CURRENT (mA)
250
300
LT1500/01 • TPC14
Maximum Load Current
(3.3V Output)
600
500
OUTPUT CURRENT (mA)
OUTPUT CURRENT (mA)
400
L
≥
33µH
300
200
100
0
1.50
L = 10µH
600
500
OUTPUT CURRENT (mA)
1.75
2.00 2.25 2.50
INPUT VOLTAGE (V)
U W
LT1500/01 • TPC11
Efficiency (5V Output)
100
90
80
70
60
50
40
Efficiency (12V Output)
I
LOAD
= 50mA
I
LOAD
= 10mA
T
J
= 25°C
L = 33µH
LOW LOSS INDUCTOR
0
2
4
6
8
INPUT VOLTAGE (V)
10
12
LT1500/01 • TPC12
LT1500/01 • TPC13
Inductor Copper Loss (5V Output)
10
V
IN
= 3V
R = 1Ω
R = 0.5Ω
Inductor Copper Loss
(12V Output)
V
IN
= 5V
R = 1Ω
R = 0.5Ω
1
1
R = 0.2Ω
0.1
0
25
50 75 100 125 150 175
LOAD CURRENT (mA)
200
LT1500/01 • TPC15
LTC1500/01 • TPC16
Maximum Load Current
(5V Output)
600
500
400
300
200
100
0
2.0
2.5
3.0
3.5
4.0
INPUT VOLTAGE (V)
4.5
5.0
Maximum Load Current
(12V Output)
L = 33µH
400
L
≥
33µH
300
L = 10µH
200
100
0
L = 100µH
L = 10µH
2.75
3.00
0
2
4
6
8
INPUT VOLTAGE (V)
10
12
LT1500/01 • TPC08
LT1500/01 • TPC09
LT1500/01 • TPC10
5
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