LTC3537
2.2 MHz, 600mA
Synchronous Step-Up DC/DC
Converter and 100mA LDO
FEATURES
High Efficiency Step-Up DC/DC Converter and LDO
Step-Up
n
V : 0.68V to 5V, V
IN
OUT
: 1.5V to 5.25V
I
OUT
: 100mA at 3.3V, V
IN
>0.8V
n
2.2MHz Fixed Frequency Operation
n
Synchronous Rectifier with Output Disconnect
n
Burst Mode Operation (Pin Selectable)
Linear LDO Regulator
n
V : 1.8V to 5.5V, V
IN
OUT
: 0.6V to 5V
I
OUT
: 100mA
n
100mV Dropout Voltage at 50mA
n
24dB Ripple Rejection at f
SW
Combined
n
Power Good Indicators
n
Low-Battery Comparator
n
30μA I
Q
n
Low Profile 3mm
×
3mm
×
0.75mm Package
n
DESCRIPTION
The LTC
®
3537 combines a high efficiency, 2.2MHz step-up
DC/DC converter with an idependent 100mA low dropout
regulator (LDO). The step-up converter starts from an input
voltage as low as 0.68V and contains an internal 0.4Ω
switch and a 0.6Ω synchronous rectifier that disconnects
from the output when disabled in shutdown.
A switching frequency of 2.2MHz minimizes solution
footprint by allowing the use of tiny, low profile inductors
and ceramic capacitors. The current mode PWM design
is internally compensated, reducing external parts count.
Fixed frequency switching is maintained until a light load
current is sensed, at which point Burst Mode
®
operation is
engaged to maximize efficiency. For low noise operation,
Burst Mode Operation can be disabled. Anti-ring circuitry
reduces EMI by damping the inductor in discontinuous
mode. Additional features include a low shutdown current
of under 1μA and thermal overload protection.
The integrated LDO regulator provides a very low noise,
programmable low dropout supply.
L,
LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
APPLICATIONS
n
n
n
n
Wireless Microphones
Portable Medical instruments
Noise Cancelling/Portable Headsets
RF and Audio Power
TYPICAL APPLICATION
Efficiency and Power Loss
vs Load Current
2.2μH
R6
665k
ALKALINE
0.8V
TO
1.6V
+
R5
1.0M
1μF
OFF ON
PWM BURST
SW
V
OUTB
3.3V
4.7μF
V
OLDO
3V
1μF
R1
1M
R3
511k
3537 TA01a
100
90
1000
V
INB
V
OUTB
R2
1.74M
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
0.1
EFFICIENCY
100
POWER LOSS (mW)
LBI LTC3537 V
INL
LBO
FBB
PGDB
PGDL
V
OLDO
ENLDO
ENBST
MODE
FBL
SGND PGND
10
R4
2.05M
POWER LOSS
1
0.1
V
IN
, MODE = 1.8V
1
100
10
LOAD CURRENT (mA)
0.01
1000
3537 TA01b
3537fa
1
LTC3537
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
V
OUTB
12 V
INL
17
11 V
OLDO
10 FBL
9 FBB
5
PGDB
6
ENBST
7
PGDL
8
ENLDO
PGND
LBO
SW
V
INB
and V
INL
Voltage................................... –0.3V to 6V
SW DC Voltage............................................. –0.3V to 6V
SW Pulsed (<100ns) Voltage ....................... –0.3V to 7V
FBB, FBL, PGDB, PGDL Voltage ................... –0.3V to 6V
MODE, ENBST, ENLDO Voltage ................... –0.3V to 6V
LBI and LBO Voltage .................................... –0.3V to 6V
V
OUTB
, V
OLDO
............................................... –0.3V to 6V
Operating Temperature (Notes 2, 5) ......... –40°C to 85°C
Junction Temperature ........................................... 125°C
Storage Temperature Range................... –65°C to 125°C
16 15 14 13
MODE 1
LBI 2
SGND 3
V
INB
4
UD PACKAGE
16-LEAD (3mm 3mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 68°C/W (Note 6)
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3537EUD#PBF
TAPE AND REEL
LTC3537EUD#TRPBF
PART MARKING
LDBD
PACKAGE DESCRIPTION
16-Lead (3mm
×
3mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to:
http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to:
http://www.linear.com/tapeandreel/
ELECTRICAL CHARACTERISTICS
SYMBOL
V
INMIN
V
OUTB
V
FBB
I
FBB
I
QSHDN
I
QACTIVE
I
QBURST
I
NLEAK
I
PLEAK
PARAMETER
Minimum Start-Up Voltage
Output Voltage Range
Feedback Voltage
Feedback Input Current
Quiescent Current - Shutdown
Quiescent Current - Active
Quiescent Current - Burst
CONDITIONS
I
LOAD
= 1mA
Boost Converter
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
INB
= 1.2V, V
OUTB
= 3.3V, unless otherwise noted.
MIN
TYP
0.68
l
l
MAX
0.8
5.25
1.240
50
1
500
UNITS
V
V
V
nA
μA
μA
μA
1.5
1.179
1.21
1
0.02
300
15
0.1
0.1
V
ENBST
= V
ENLDO
= 0V, Not Including SW Leakage,
V
OUTB
= 0V
Measured on V
OUTB
, Nonswitching, MODE = 1.2V,
V
ENLDO
= 0V
Measured on V
OUTB
, FBB >1.24V, MODE = 1.2V,
V
ENLDO
= 0V
NMOS Switch Leakage Current V
SW
= 5V
PMOS Switch Leakage Current V
SW
= 5V, V
OUTB
= 0V
5
10
μA
μA
3537fa
2
LTC3537
ELECTRICAL CHARACTERISTICS
SYMBOL
R
NMOS
PARAMETER
NMOS Switch On Resistance
CONDITIONS
V
OUTB
= 1.8V
V
OUTB
= 3.3V
V
OUTB
= 5V
V
OUTB
= 1.8V
V
OUTB
= 3.3V
V
OUTB
= 5V
(Note 4)
(Note 3)
V
FBB
= 1.15V
V
FBB
= 1.3V
l
l
l
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
INB
= 1.2V, V
OUTB
= 3.3V, unless otherwise noted.
MIN
TYP
0.8
0.4
0.3
1
0.6
0.4
600
750
40
87
2
0.8
0.3
V
ENBST
= 5.5V
0.8
0.3
V
MODE
= 5.5V
Falling Threshold
V
LBI
= 1V
I
LBO
= 5mA
V
LBO
= 5.5V
I
PGDB
= 5mA
V
PGDB
= 5.5V
V
FBB
Rising
530
1.5
0.5
553
35
10
200
0.01
200
0.01
94
6
1
1
50
575
1.5
92
0
2.2
2.4
MAX
UNITS
Ω
Ω
Ω
Ω
Ω
Ω
mA
ns
%
%
MHz
V
V
μA
V
V
μA
ms
mV
mV
nA
mV
μA
mV
μA
% V
OUTB
%
R
PMOS
PMOS Switch On Resistance
I
LIM
t
LIMDELAY
NMOS Current Limit
Current Limit Delay Time to
Output
Max Duty Cycle
Min Duty Cycle
f
SW
V
ENBSTH
V
ENBSTL
I
ENBSTIN
V
MODEH
V
MODEL
I
MODEIN
t
SS
V
FBLBI
I
LBIIN
V
LBOLOW
I
LBOLEAK
V
PGDBLOW
I
PGDBLEAK
Switching Frequency
ENBST Input High Voltage
ENBST Input Low Voltage
ENBST Input Current
MODE Input High Voltage
MODE Input Low Voltage
MODE Input Current
Soft-Start Time
LBI Feedback Voltage
LBI Hysteresis Voltage
LBI Input Current
LBO Voltage Low
LBO Leakage Current
PGDB Voltage Low
PGDB Leakage Current
PGDB Trip Point Voltage
PGDB Hysteresis
The
l
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T
A
= 25°C.
V
INL
= 3.3V, V
OLDO
= 3V, unless otherwise noted.
SYMBOL
V
INL
V
OLDO
I
OUTMAX
V
FBL
PARAMETER
Input Voltage Range
Output Voltage Range
Max Output Current
Feedback Voltage
Line Regulation
Load Regulation
V
DROPOUT
Dropout Voltage
V
INL
= 1.8V to 5.5V
I
LOAD
= 10mA to 90mA
I
O
= 50mA
I
LOAD
= 100mA
l
l
CONDITIONS
MIN
1.8
V
FBL
100
590
TYP
MAX
5.5
5
UNITS
V
V
mA
mV
%
%
mV
LDO Regulator
600
0.1
0.4
100
610
3537fa
3
LTC3537
ELECTRICAL CHARACTERISTICS
SYMBOL
PSRR
I
SHORT
V
ENLDOH
V
ENLDOL
I
ENLDO
V
PGDLLOW
I
PGDLLEAK
PARAMETER
Ripple Rejection
Short Circuit Current Limit
ENLDO Input High Voltage
ENLDO Input Low Voltage
ENLDO Input Current
PGDL Voltage Low
PGDL Leakage Current
PGDL Trip Point
PGDL Hysteresis
Note 1:
Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2:
The LTC3537 is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
Specification is guaranteed by design and not 100% tested in
production.
V
ENLDO
= 5.5V
I
PGDL
= 5mA
V
PGDL
= 5.5V
V
FBL
Rising
1.5
200
0.01
96
3
1
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
INL
= 3.3V, V
OLDO
= 3V, unless otherwise noted.
CONDITIONS
f = 2.2MHz at I
LOAD
= 100mA (Note 3)
V
OLDO
= 0V
l
MIN
110
0.8
TYP
24
150
MAX
UNITS
dB
mA
V
0.3
V
μA
mV
μA
% V
OLDO
%
Note 4:
Current measurements are made when the output is not switching.
Note 5:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may result in device degradation or failure.
Note 6:
Failure to solder the exposed backside of the package to the PC
board ground plane will result in a thermal resistance much higher than
68°C/W.
3537fa
4
LTC3537
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency vs Load Current and
V
INB
for V
OUTB
= 1.8V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
10
100
POWER LOSS (mW)
EFFICIENCY (%)
1000
100
90
80
70
60
50
40
30
20
10
0
0.01
10
100
POWER LOSS (mW)
T
A
= 25°C unless otherwise noted.
Efficiency vs Load Current and
V
INB
for V
OUTB
= 3.3V
1000
100
90
80
70
I
IN
(μA)
60
50
40
30
20
No-Load Input Current vs V
INB
V
OUTB
= 3.3V
1
V
INB
= 1V
V
INB
= 1.2V
V
INB
= 1.5V
0.1
PLOSS AT V
INB
= 1V
PLOSS AT V
INB
= 1.2V
PLOSS AT V
INB
= 1.5V
0.01
1
100
1000
0.1
10
LOAD CURRENT (mA)
3537 G01
V
INB
= 1.2V
V
INB
= 1.8V 1
V
INB
= 2.4V
V
INB
= 2.8V
PLOSS AT V
INB
= 1.2V 0.1
PLOSS AT V
INB
= 1.8V
PLOSS AT V
INB
= 2.4V
PLOSS AT V
INB
= 2.8V
0.01
0.1
10
1
100
1000
LOAD CURRENT (mA)
3537 G02
10
0.5
1
1.5
2
2.5
V
INB
(V)
3
3.5
3537 G03
Efficiency vs Load Current and
V
INB
for V
OUTB
= 5V
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.01
10
100
LOAD CURRENT (mA)
POWER LOSS (mW)
1000
1000
900
800
700
600
500
400
300
200
100
Maximum Output Current vs V
INB
1000
V
OUTB
= 5V
Minimum Load Resistance During
Start-Up vs V
INB
V
OUTB
= 3.3V
LOAD (Ω)
V
OUTB
= 2.5V
V
OUTB
= 1.8V
1
2
4
4.5
3537 G05
V
INB
= 1.2V
V
INB
= 2.4V 1
V
INB
= 3.6V
V
INB
= 4.2V
PLOSS AT V
INB
= 1.2V 0.1
PLOSS AT V
INB
= 2.4V
PLOSS AT V
INB
= 3.6V
PLOSS AT V
INB
= 4.2V
0.01
0.1
10
1
100
1000
LOAD CURRENT (mA)
3537 G04
100
0
0.5
1.5
2.5 3
V
INB
(V)
3.5
10
0.8 0.9
1
1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8
V
INB
(V)
3537 G06
Start-Up Delay Time vs V
INB
60
50
LOAD CURRENT (mA)
40
DELAY (μs)
30
20
10
0
35
Burst Mode Threshold Current
vs V
INB
V
OUTB
= 1.8V
C
OUT
= 4.7μF
30
L = 2.2μH
LOAD CURRENT (mA)
25
20
15
10
5
0
0.8
LEAVE BURST
45
Burst Mode Threshold Current
vs V
INB
V
OUTB
= 2.5V
40 C
OUT
= 4.7μF
L = 2.2μH
35
30
25
20
15
10
ENTER BURST
LEAVE BURST
ENTER BURST
0.9
1
1.1 1.2
V
INB
(V)
1.3
1.4
1.5
3537 G08
5
0
0.8
1
1.2
1.4
1.6
V
INB
(V)
1.8
2
3537 G09
1
1.5
2
2.5
3
V
INB
(V)
3.5
4
4.5
5
3537 G07
3537fa
5
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