LTC3537
2.2 MHz, 600mA
Synchronous Step-Up DC/DC
Converter and 100mA LDO
FEATURES
DESCRIPTION
TheLTC®3537combinesahighefficiency,2.2MHzstep-up
DC/DC converter with an idependent 100mA low dropout
regulator(LDO).Thestep-upconverterstartsfromaninput
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.
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High Efficiency Step-Up DC/DC Converter and LDO
Step-Up
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V : 0.68V to 5V, V : 1.5V to 5.25V
OUT
2.2MHz Fixed Frequency Operation
Synchronous Rectifier with Output Disconnect
Burst Mode Operation (Pin Selectable)
IN
OUT
I
: 100mA at 3.3V, V >0.8V
IN
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n
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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.
Linear LDO Regulator
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V : 1.8V to 5.5V, V : 0.6V to 5V
OUT
100mV Dropout Voltage at 50mA
24dB Ripple Rejection at f
IN
OUT
I
: 100mA
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SW
Combined
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Power Good Indicators
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n
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Low-Battery Comparator
30μA I
Q
Low Profile 3mm × 3mm × 0.75mm Package
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
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Wireless Microphones
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Portable Medical instruments
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Noise Cancelling/Portable Headsets
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RF and Audio Power
TYPICAL APPLICATION
Efficiency and Power Loss
vs Load Current
100
90
80
70
60
50
40
30
20
10
0
1000
100
10
2.2μH
R6
V
SW
LTC3537
OUTB
V
INB
V
OUTB
665k
3.3V
EFFICIENCY
R2
LBI
LBO
V
ALKALINE
0.8V
INL
+
1.74M
4.7μF
R5
1.0M
TO
FBB
PGDB
PGDL
ENLDO
ENBST
MODE
1.6V
V
3V
OLDO
V
OLDO
1μF
1
POWER LOSS
R4
OFF ON
PWM BURST
2.05M
1μF
FBL
0.1
R1
1M
R3
511k
SGND PGND
V
IN
, MODE = 1.8V
0.01
0.01
0.1
1
10
100
1000
3537 TA01a
LOAD CURRENT (mA)
3537 TA01b
3537fa
1