LTC3538
800mA Synchronous
Buck-Boost
DC/DC Converter
FEATURES
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DESCRIPTION
The LTC
®
3538 is a highly efficient, low noise, buck-boost
DC/DC converter that operates from input voltages above,
below, and equal to the output voltage. The topology
incorporated in the IC provides a continuous transfer
function through all operating modes, making the product
ideal for single Lithium Ion or multicell Alkaline or NiMH
applications where the output voltage is within the battery
voltage range.
The LTC3538 is suited for use in Micro Hard Disk Drive
(μHDD) applications with its 800mA current capability. Burst
Mode
®
operation provides high efficiency at light loads.
The LTC3538 includes two 0.17Ω N-channel and two
0.2Ω P-channel MOSFET switches. Operating frequency
is internally set to 1MHz to minimize solution footprint
while maximizing efficiency.
Other features include <5μA shutdown current, internal
soft-start, short circuit protection and thermal shutdown.
The LTC3538 is available in a low profile (0.75mm), ther-
mally enhanced 8-lead (2mm × 3mm) DFN package.
, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology
Corporation. All other trademarks are the property of their respective owners. Protected by
U.S. Patents including 5481178, 6304066, 6580258, 6166527, 6404251.
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Regulated Output with Input Voltages Above,
Below, or Equal to the Output
800mA Continuous Output Current from a Single
Lithium-Ion/Polymer Cell
Single Inductor
1.8V to 5.25V V
OUT
Range
2.4V to 5.5V V
IN
Range
1MHz Fixed Frequency Operation
Output Disconnect in Shutdown
35μA Quiesecent Current in Burst Mode Operation
<5μA Shutdown Current
Internal Soft-Start
Small, Thermally Enhanced 8-Lead (2mm x 3mm)
DFN package
APPLICATIONS
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Miniature Hard Disk Drives
MP3 Players
Digital Cameras
Cellular Handsets
PDAs, Handheld PC
GPS Receivers
TYPICAL APPLICATION
Li-Ion/Polymer to 3.3V at 800mA
L1
3.3μH
V
OUT
3.3V
800mA
Efficiency vs V
IN
100
V
OUT
= 3.3V
I
LOAD
= 200mA
LTC3538
SW1
V
IN
2.9V TO 4.2V
C
IN
10μF
PWM
BURST
BURST
GND
ON OFF
SD
V
IN
SW2
V
OUT
FB
V
C
330pF
33pF
C
OUT
22μF
15k
EFFICIENCY (%)
R1
464k
10k
95
90
85
*
R2
200k
3538 TA01
80
2.4
2.9
3.4
4.4
3.9
V
IN
(V)
4.9
5.4
3538 TA01b
*μP OPEN DRAIN I/O
3538fb
1
LTC3538
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
FB 1
VC 2
GND 3
BURST 4
9
8 V
IN
7 SW1
6 SW2
5 V
OUT
V
IN
,V
OUT
Voltage .......................................... –0.3V to 6V
SW1,SW2 Voltage
DC............................................................ –0.3V to 6V
Pulsed < 100ns ........................................ –0.3V to 7V
BURST, FB, VC Voltage ................................. –0.3V to 6V
Operating Temperature (Note 2)............... –40°C to 85°C
Maximum Junction Temperature (Note 3)............. 125°C
Storage Temperature Range................... –65°C to 125°C
DCB PACKAGE
8-LEAD (2mm × 3mm) PLASTIC DFN
T
JMAX
= 125°C
θ
JA
= 75°C/W 4-LAYER BOARD,
θ
JC
= 13.5°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LTC3538EDCB#PBF
LEAD BASED FINISH
LTC3538EDCB
TAPE AND REEL
LTC3538EDCB#TRPBF
TAPE AND REEL
LTC3538EDCB#TR
PART MARKING
LCRB
PART MARKING
LCRB
PACKAGE DESCRIPTION
8-Lead (2mm × 3mm) Plastic DFN
PACKAGE DESCRIPTION
8-Lead (2mm × 3mm) Plastic DFN
TEMPERATURE RANGE
–40°C to 85°C
TEMPERATURE RANGE
–40°C to 85°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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
PARAMETER
Input Voltage
Feedback Voltage
Feedback Input Current
V
IN
Quiescent Current – Shutdown
V
IN
Quiescent Current – Active
V
IN
Quiescent Current – Sleep
NMOS Switch Leakage
PMOS Switch Leakage
NMOS Switch On-Resistance
PMOS Switch On-Resistance
Input Current Limit
Reverse Current Limit
Burst Mode Operational Peak Current
Maximum Duty Cycle
(Note 4)
(Note 4)
CONDITIONS
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= V
OUT
= 3.6V, BURST = 0V, unless otherwise noted.
MIN
●
●
TYP
1.00
1
1.5
1
35
0.1
0.1
0.17
0.2
MAX
5.5
1.020
50
5
1.8
60
7
10
UNITS
V
V
nA
μA
mA
μA
μA
μA
Ω
Ω
A
A
A
%
%
%
3538fb
2.4
0.980
V
C
= 0V, Not Including Switch Leakage
FB = 0.8V
FB = 1.2V, BURST = V
IN
Switches B and C
Switches A and D
Switches B and C
Switches A and D
●
1.4
2
0.5
0.9
Boost (%Switch C On)
Buck (% Switch A On)
Buck (% Switch D On)
●
●
●
70
100
100
88
2
LTC3538
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= V
OUT
= 3.6V, unless otherwise noted.
PARAMETER
Minimum Duty Cycle
Frequency Accuracy
Internal Soft-Start Time
Error Amp A
VOL
Error Amp Source Current
Error Amp Sink Current
V
C
Shutdown Threshold (Off)
V
C
Output Current in Shutdown
BURST Threshold (High)
BURST Threshold (Low)
BURST Input Current
V
BURST
= 3.6V
V
C
= 1.5V, FB = OV
V
C
= 1.5V, FB = 1.2V
IC is Disabled
V
C
= GND
●
●
●
ELECTRICAL CHARACTERISTICS
CONDITIONS
FB = 1.2V
MIN
●
●
TYP
1
1.5
80
–13
130
MAX
0
1.2
UNITS
%
MHz
ms
dB
μA
μA
0.8
0.25
–1
1.4
0.4
0.1
1
–3
V
μA
V
V
μA
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 LTC3538 is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
This IC includes over-temperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when over-temperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may result in device degradation or failure.
Note 4:
The IC is tested in a feedback loop to make the measurement.
TYPICAL PERFORMANCE CHARACTERISTICS
Li-Ion to 3.3V Efficiency
100
90
80
EFFICIENCY (%)
EFFICIENCY (%)
70
60
50
40
30
20
10
0.1
1
V
IN
= 2.7V
V
IN
= 3.6V
V
IN
= 4.2V
10
100
LOAD CURRENT (mA)
1000
3538 G01
T
A
= 25°C unless otherwise noted
Switch Pins Before Entering
Boost Mode
1000
SW1
2V/DIV
Efficiency and Power Loss vs
Load Current
100
90
80
70
60
50
40
30
20
10
0
0.1
1
10
100
LOAD CURRENT (mA)
0.1
1000
3538 G02
FIXED FREQUENCY
Burst Mode
OPERATION
100
POWER LOSS (mW)
SW2
2V/DIV
50ns/DIV
V
IN
= 2.9V
V
OUT
= 3.3V AT 500mA
3538 G03
Burst Mode
OPERATION
10
POWER LOSS
FIXED FREQUENCY
1
POWER LOSS BURST
3538fb
3
LTC3538
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Pins Before Entering
Buck Mode
V
IN
= 2.5V
Burst Mode SLEEP CURRENT (μA)
SW1
2V/DIV
V
IN
= 3.3V
SW2
2V/DIV
V
IN
= 4.2V
50ns/DIV
V
IN
= 3.9V
V
OUT
= 3.3V AT 500mA
3538 G04
T
A
= 25°C unless otherwise noted
Burst Mode Sleep Current vs
Temperature
45
V
OUT
Ripple in Buck, Buck-Boost
and Boost Modes at 500mA Load
40
35
1μs/DIV
V
OUT
= 3.3V, AC-COUPLED
20mV/DIV
C
OUT
= 22μF
I
LOAD
= 500mA
3538 G05
30
25
20
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
3538 G16
Error Amplifier Source Current vs
Temperature
–12.5
OSCILLATOR FREQUENCY (kHz)
1025
Oscillator Frequency vs
Temperature
V
IN
= V
OUT
= 3.6V
1.010
Feedback Voltage vs Temperature
V
C
SOURCE CURRENT (μA)
–13.0
1.005
FB VOLTAGE (V)
–13.5
1000
1.000
–14.0
0.995
–14.5
–15.0
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
3538 G06
975
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
3538 G07
0.990
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
3538 G08
Maximum Output Current
Capability vs V
IN
1800
OUTPUT CURRENT CAPABILITY (mA)
1600
FB LINE REGULATION (%)
1400
1200
1000
800
600
400
200
0
2.0
2.5
3.0
3.5 4.0
V
IN
(V)
4.5
5.0
5.5
3538 G17
Feedback Voltage Line
Regulation
0.4
0.3
0.2
0.1
0
V
IN
START VOLTAGE (V)
V
OUT
= 3.3V
2.3045
2.3040
2.3035
2.3030
2.3025
2.3020
2.3015
2.3010
Minimum Start-Up Voltage
V
OUT
= 3.3V
–0.1
–0.2
2.4
3.4
V
IN
(V)
4.4
5.4
3538 G09
2.3005
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
3538 G10
3538fb
4
LTC3538
TYPICAL PERFORMANCE CHARACTERISTICS
V
C
On/Off Threshold vs
Temperature
0.80
0.75
V
C
ON/OFF THRESHOLD (V)
0.70
0.65
0.60
0.55
V
C
OFF THRESHOLD
0.50
0.45
0.40
–50
0
50
TEMPERATURE (°C)
100
3538 G10
T
A
= 25°C unless otherwise noted
Load Transient in Fixed
Frequency Mode
V
OUT
100mV/DIV
Current Limit vs Temperature
4.0
V
IN
= V
OUT
= 3.6V
PEAK CURRENT LIMIT
I
LOAD
200mA/DIV
3.5
V
C
ON THRESHOLD
CURRENT LIMIT (A)
3.0
2.5
100μs/DIV
2.0
LINEAR CURRENT LIMIT
1.5
–50
–25
0
25
50
TEMPERATURE (°C)
75
100
3538 G12
3538 G13
V
IN
= 3.3V
V
OUT
= 3.3V
I
LOAD
= 0mA TO 500mA
C
OUT
= 22μF X5R CERAMIC
Burst Mode Operation
BURST
2V/DIV
Transition From Burst Mode
Operation to Fixed Frequency
V
OUT
50mV/DIV
I
L
500mA/DIV
10μs/DIV
V
IN
= 3.3V
V
OUT
= 3.3V
I
LOAD
= 10mA
C
OUT
= 22μF X5R CERAMIC
3538 G14
V
OUT
100mV/DIV
50μs/DIV
V
IN
= 3.3V
V
OUT
= 3.3V
I
LOAD
= 30mA
C
OUT
= 22μF X5R CERAMIC
3538 G15
3538fb
5
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