LINER LTC3443 Micropower synchronous buck-boost dc/dc converter Datasheet

LTC3532
Micropower Synchronous
Buck-Boost DC/DC Converter
DESCRIPTIO
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FEATURES
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Single Inductor
Regulated Output with Input Voltages Above, Below
or Equal to the Output
Wide VIN Range: 2.4V to 5.5V
VOUT Range: 2.4V to 5.25V
Up to 500mA Peak Output Current
Synchronous Rectification: Up to 95% Efficiency
Manual or Programmable Automatic Burst Mode®
Operation
Output Disconnect in Shutdown
Programmable Oscillator: 300kHz to 2MHz
Pin Compatible with LTC3440
Small Thermally Enhanced 10-Lead (3mm × 3mm)
DFN and 10-Lead MSOP Packages
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APPLICATIO S
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The LTC®3532 is a high efficiency, fixed frequency, buckboost DC/DC converter that operates from input voltages
above, below or 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, multicell alkaline or NiMH applications where the output voltage is within the battery
voltage range.
The device includes two 0.36Ω N-channel MOSFET
switches and two 0.42Ω P-channel switches. Switching
frequencies up to 2MHz are programmed with an external
resistor. Quiescent current is only 35μA in Burst Mode
operation, maximizing battery life in portable applications. Automatic Burst Mode operation allows the user
to program the load current for Burst Mode operation or
to control it manually.
Other features include a 1μA shutdown, soft-start control,
thermal shutdown, and peak current limit. The LTC3532 is
available in a low profile (0.75mm) 10-lead (3mm × 3mm)
DFN and 10-lead MSOP packages.
Miniature Hard Disk Drive Power Supply
MP3 Players
Handheld Instruments
Digital Cameras
Handheld Terminals
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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TYPICAL APPLICATIO
Miniature Hard Disk Drive Power Supply
4.7μH
VIN
Li-Ion
2.5V TO 4.2V
SW1
SW2
VIN
VOUT
SHDN/SS LTC3532
FB
BURST
VC
340k
200k
4.7μF
43.2k
GND
VOUT
200mV/DIV
ILOAD
100mA/DIV
33pF
12.1k
RT
1k
VOUT
3.3V
100mA
TO 500mA
(PEAK)
220pF
10μF
200k
100μs/DIV
VIN = 3V
VOUT = 3.3V
ILOAD = 50mA TO 300mA
3532 TA01b
0.01μF
3532 TA01
3532fc
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LTC3532
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ABSOLUTE
AXI U RATI GS (Note 1)
BURST, VIN, VOUT, VC, FB ................................... –0.3V to 6V
RT ..................................................................... 0V to 5V
SHDN/SS ..................................................... –0.3V to 6V
SW1, SW2
DC............................................................ –0.3V to 6V
Pulsed < 100ns ........................................ –0.3V to 7V
Operating Temperature Range (Note 2).... –40°C to 85°C
Maximum Junction Temperature (Note 4)............. 125°C
Storage Temperature Range
DD ..................................................... –65°C to 125°C
MSOP ................................................ –65°C to 150°C
Lead Temperature (Soldering,10 sec)
MSOP ............................................................... 300°C
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PI CO FIGURATIO
TOP VIEW
TOP VIEW
1
10 VC
BURST
2
9 FB
SW1
3
SW2
4
7 VIN
GND
5
6 VOUT
RT
11
RT
BURST
SW1
SW2
GND
8 SHDN/SS
10
9
8
7
6
1
2
3
4
5
VC
FB
SHDN/SS
VIN
VOUT
MS PACKAGE
10-LEAD PLASTIC MSOP
TJMAX = 125°C
θJA = 130°C/W 1 LAYER BOARD
θJA = 100°C/W 4 LAYER BOARD
θJC = 45°C/W
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
TJMAX = 125°C, θJA = 43°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE CONNECTED TO PCB
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ORDER I FOR ATIO
LEAD FREE FINISH
TAPE AND REEL
PART MARKING
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LTC3532EDD#PBF
LTC3532EDD#TRPBF
LBXR
10-Lead (3mm × 3mm) Plastic DFN
–40°C to 85°C
LTC3532EMS#PBF
LTC3532EMS#TRPBF
LTBXS
10-Lead Plastic MSOP
–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
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT = 3.6V, RT = 64.9k, unless otherwise specified.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Input Start-Up Voltage
●
2.4
V
Input Operating Range
●
2.4
5.5
V
Output Voltage Adjust Range
●
2.4
5.25
V
Feedback Voltage
●
1.19
1.22
1.25
V
1
50
nA
Feedback Input Current
VFB = 1.22V
2.3
Quiescent Current, Burst Mode Operation
BURST = 0V
35
60
μA
Quiescent Current, Shutdown
SHDN = 0V, Not Including Switch Leakage, VOUT = 0V
0.1
1
μA
Quiescent Current, Active
VC = 0V, BURST = VIN (Note 3)
600
1000
μA
NMOS Switch Leakage
Switches B and C
0.1
5
μA
3532fc
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LTC3532
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = VOUT = 3.6V, RT = 64.9k, unless otherwise specified.
PARAMETER
CONDITIONS
TYP
MAX
PMOS Switch Leakage
Switches A and D
MIN
0.1
10
NMOS Switch On Resistance
Switches B and C
0.36
Ω
PMOS Switch On Resistance
Switches A and D
0.42
Ω
Input Current Limit
Maximum Duty Cycle
●
●
Boost (% Switch C On)
Buck (% Switch A On)
Minimum Duty Cycle
●
Frequency Accuracy
●
0.8
1.1
70
100
88
575
740
UNITS
μA
1.45
A
%
%
0
%
885
kHz
Burst Threshold (Falling)
0.88
V
Burst Threshold (Rising)
1.12
V
Ratio of IOUT to IBURST
Burst Current Ratio
8000
Error Amp AVOL
VC = 1.4V
Error Amp Source Current
Error Amp Sink Current
VC = 2V
SHDN/SS Threshold
When IC is Enabled
When EA is at Maximum Boost Duty Cycle
SHDN/SS Input Current
VSHDN = 5.5V
●
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60
3V
3.6V
4.2V
50
VOUT = 3.3V
40
0.1
1
10
100
LOAD CURRENT (mA)
0.1
0.01
1000
3532 G01
EFFICIENCY (%)
EFFICIENCY (%)
1
80
10
70
60
BURST
POWER LOSS
FIXED FREQUENCY
POWER LOSS
1
50
40
0.1
FIXED FREQUENCY
EFFICIENCY
1
1.5
V
V
0.01
1
μA
10
100
LOAD CURRENT (mA)
0.1
1000
80
3.0
75
2.5
2000kHz
70
1500kHz
2.0
65
1000kHz
1.5
60
55
1.0
50
500kHz
0.5
0
BURST MODE
2.5
45
NOT SWITCHING
3.5
4.5
5.5
40
VIN QUIESCENT CURRENT BURST MODE (μA)
POWER LOSS
100
POWER LOSS (mW)
10
1000
90 BURST EFFICIENCY
POWER LOSS (mW)
80
μA
1
2.2
Fixed Frequency and Burst Mode
Quiescent Current vs VIN
100
100
70
0.4
Efficiency and Power Loss
vs Load
EFFICIENCY
μA
TA = 25°C, unless otherwise specified.
VIN QUIESCENT CURRENT (mA)
Efficiency and Power Loss
vs Load Autoburst Mode
90
15
Note 3: Current measurements are performed when the outputs are not
switching.
Note 4: 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.
TYPICAL PERFOR A CE CHARACTERISTICS
1000
dB
310
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 LTC3532E 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 correlations
with statistical process controls.
100
90
VIN (V)
3532 G02
3532 G03
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LTC3532
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TYPICAL PERFOR A CE CHARACTERISTICS
Peak Current Clamp and Limit
vs VIN
100
1.6
98
1.4
INPUT CURRENT (A)
96
94
92
90
88
86
Automatic Burst Threshold
vs RBURST
70
60
1.2
LOAD CURRENT (mA)
Efficiency vs Frequency
EFFICIENCY (%)
TA = 25°C, unless otherwise specified.
ILIMIT
1.0
ICLAMP
0.8
0.6
40
LEAVE BURST
30
0.4
84
20
0.2
82 VIN = 3.6V
VOUT = 3.3V
80
1500
500
1000
FREQUENCY (kHz)
VOUT = 3.3V
VIN = 3.6V
VOUT = 3.3V
0
2.4
2000
3.4
5.4
4.4
10
150
VIN (V)
3532 G04
1200
1.241
1150
1.236
FEEDBACK VOLTAGE (V)
1050
1000
950
900
850
Load Transient Response in
Fixed Frequency Mode
VOUT
200mV/DIV
1.231
1.226
1.221
1.216
ILOAD
100mA/DIV
1.211
1.206
100μs/DIV
1.201
VIN = 3.6V
800
–5
–55
1.196
–55
95
45
TEMPERATURE (°C)
–5
45
TEMPERATURE (°C)
3532 G07
95
Switch Pins Before Entering
Boost Mode
Switch Pins in Buck-Boost Mode
VOUT
200mV/DIV
SW1
2V/DIV
SW1
2V/DIV
BURST PIN
2V/DIV
SW2
2V/DIV
SW2
2V/DIV
COUT = 22μF
VIN = 3.6V
VOUT = 3.3V
3535 G09
COUT = 10μF
VIN = 3.6V
VOUT = 3.3V
3532 G08
Burst Mode to Fixed Frequency
Transition
400μs/DIV
550
3532 G06
Feedback Voltage vs Temperature
1100
ENTER BURST
250
350
450
BURST RESISTOR (kΩ)
3532 G05
Frequency vs Temperature
FREQUENCY (MHz)
50
3532 G10
40ns/DIV
VIN = 3.3V
VOUT = 3.3V
ILOAD = 100mA
3532 G11
40ns/DIV
3532 G12
VIN = 2.9V
VOUT = 3.3V
ILOAD = 100mA
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LTC3532
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TYPICAL PERFOR A CE CHARACTERISTICS
Switch Pins Before Entering
Buck Mode
TA = 25°C, unless otherwise specified.
Output Ripple at 100mA Load
SW1
2VDIV
VOUT
50mV/DIV
Burst Mode, Boost
VIN = 2.4V
SW1
5V/DIV
VIN = 3.6V
SW2
5V/DIV
VIN = 4.5V
VOUT
100mV/DIV
VOUT
50mV/DIV
SW2
2VDIV
VOUT
50mV/DIV
40ns/DIV
INDUCTOR
CURRENT
500mA/DIV
3535 G13
VIN = 4V
VOUT = 3.3V
ILOAD = 100mA
400ns/DIV
3535 G14
4μs/DIV
3535 G15
VIN = 2.4V
VOUT = 3.3V
ILOAD = 20mA
COUT = 22μF
VOUT = 3.6V
IOUT = 100mA
COUT = 10μF
Burst Mode, Buck-Boost
Burst Mode, Buck
SW1
5V/DIV
SW1
5V/DIV
SW2
5V/DIV
SW2
5V/DIV
VOUT
100mV/DIV
VOUT
100mV/DIV
INDUCTOR
CURRENT
500mA/DIV
INDUCTOR
CURRENT
500mA/DIV
4μs/DIV
340612 G16
VIN = 3.75V
VOUT = 3.3V
ILOAD = 20mA
COUT = 22μF
4μs/DIV
3535 G17
VIN = 4.2V
VOUT = 3.3V
ILOAD = 20mA
COUT = 22μF
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PI FU CTIO S
RT (Pin 1): Timing Resistor to Program the Oscillator
Frequency. The programming range is 300kHz to 2MHz.
f(kHz) =
48,000
RT (kΩ)
BURST (Pin 2): Used to Set the Automatic Burst Mode Operation Threshold. Place a resistor and capacitor in parallel
from this pin to ground. See the Applications Information
section for component value selection. For manual control,
ground the pin to force Burst Mode operation, connect to
VOUT to force fixed frequency mode.
SW1 (Pin 3): Switch Pin Where the Internal Switches A
and B are Connected. Connect inductor from SW1 to SW2.
An optional Schottky diode can be connected from SW1
to ground. Minimize trace length to minimize EMI.
SW2 (Pin 4): Switch Pin Where the Internal Switches C
and D are Connected. For applications with output voltages
over 4.3V, a Schottky diode is required from SW2 to VOUT
to ensure SW2 does not exhibit excess voltage.
GND (Pin 5): Signal and Power Ground for the IC.
VOUT (Pin 6): Output of the Synchronous Rectifier. A filter
capacitor is placed from VOUT to GND.
VIN (Pin 7): Input Supply Pin. Supplies current to the
inductor through SW1 and supplies internal VCC for the
IC. A ceramic bypass capacitor as close to the VIN pin and
GND (Pin 5) is required.
3532fc
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LTC3532
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PI FU CTIO S
SHDN/SS (Pin 8): Combined Soft-Start and Shutdown.
Grounding this pin shuts down the IC. Tie to >1.5V to
enable the IC and >2.4V to ensure the error amp is not
clamped from soft-start. For Burst Mode operation, this pin
must be pulled up to within 0.5V of VIN. An RC from the
shutdown command signal to this pin will provide a softstart function by limiting the rise time of the VC pin.
VOUT =
1.22V • (R1+ R2)
R2
VC (Pin10): Error Amp Output: A frequency compensation network is connected from this pin to the FB pin to
compensate the loop. Refer to the Applications Information
section for component value selection.
FB (Pin 9): Feedback Pin. Connect resistor divider tap
here. The output voltage can be adjusted from 2.4V to
5.25V. The feedback reference is typically 1.22V. Set VOUT
according to the formula:
Exposed Pad (Pin11): The exposed pad (DFN Package)
must be soldered to PCB ground for electrical contact and
rated thermal performance.
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BLOCK DIAGRA
3
SW2
SW D
SW A
VOUT
6
SW B
GATE
DRIVERS
AND
ANTICROSS
CONDUCTION
SW C
–
7
+
VIN
4
SW1
REVERSE
AMP
+
gm = 1/60k
–
1A
+
PEAK CURRENT
LIMIT
–
+
ERROR
AMP
–
PWM
LOGIC
2.3V
–
VC
PWM COMP
UVLO
10
+
+
AUTOMATIC
Burst Mode
CONTROL AND
VC HOLD
SLEEP
RT
1
9
–
VIN
FB
+
–
1.1A
1.22V
OSC
BURST
2
VIN
8
SHDN/SS
SHUTDOWN
SOFT-START
VREF
VCC
SS
1.22V
VREF
THERMAL
SHUTDOWN
SHUTDOWN
5
GND
3532 BD
3532fc
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LTC3532
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OPERATIO
The LTC3532 provides high efficiency, low noise power
for applications such as portable instrumentation, digital
cameras, and MP3 players. The LTC proprietary topology
allows input voltages above, below or equal to the output
voltage by properly phasing the output switches. The error
amp output voltage on VC determines the output duty cycle
of the switches. Since VC is a filtered signal, it provides
rejection of frequencies well below the switching frequency.
The low RDS(ON), low gate charge synchronous switches
provide high frequency pulse width modulation control at
high efficiency. Schottky diodes across the synchronous
switch D and synchronous switch B are not required, but
provide a lower voltage drop during the break-before-make
time (typically 15ns). Schottky diodes will improve peak
efficiency by typically 1% to 2%. High efficiency is achieved
at light loads when Burst Mode operation is entered and
the IC’s quiescent current drops to a low 35μA.
LOW NOISE FIXED FREQUENCY OPERATION
Oscillator
The frequency of operation is programmed by an external
resistor from RT to ground, according to the following
equation:
f(kHz) =
48,000
RT (kΩ)
Error Amp
The error amplifier is a voltage mode amplifier. The loop
compensation components are configured around the
amplifier (from FB to VC) to obtain stability of the converter.
For improved bandwidth, an additional RC feedforward
network can be placed across the upper feedback divider
resistor. The voltage on SHDN/SS clamps the error amp
output, VC, to provide a soft-start function.
cally 50ns. A second amplifier will begin to source current
into the FB pin to drop the output voltage once the peak
input current exceeds 1A typical. This method provides a
closed loop means of clamping the input current. During
conditions where VOUT is near ground, such as during a
short-circuit or during startup, this threshold is cut in half
providing a fold back feature. For this current limit feature
to be most effective, the Thevenin resistance from FB to
ground should be greater than 100k.
Reverse Current Limit
During fixed frequency operation, the LTC3532 operates in
forced continuous conduction mode. The reverse current
limit amplifier monitors the inductor current from the output through switch D. Once the negative inductor current
exceeds 340mA typical, the IC will shut off switch D.
4-Switch Control
Figure 1 shows a simplified diagram of how the four internal
switches are connected to the inductor, VIN, VOUT and GND.
Figure 2 shows the regions of operation for the LTC3532 as
a function of the internal control voltage, VCI. Depending
on the control voltage, the IC will operate in either buck,
buck/boost or boost mode. The VCI voltage is a level shifted
voltage from the output of the error amp (VC) (see Figure
5). The four power switches are properly phased so the
transfer between operating modes is continuous, smooth
and transparent to the user. When VIN approaches VOUT
the buck/boost region is reached where the conduction
time of the 4-switch region is typically 150ns. Referring
to Figures 1 and 2, the various regions of operation will
now be described.
VIN
VOUT
7
6
PMOS D
PMOS A
Internal Current Limit
There are two different current limit circuits in the LTC3532.
They have internally fixed thresholds which vary inversely
with VIN. The first circuit is a high speed peak current limit
comparator that will shut off switch A if the current exceeds
1.1A typical. The delay to output of this amplifier is typi-
SW1
SW2
3
4
NMOS B
NMOS C
3532 F01
Figure 1. Simplified Diagram of Output Switches
3532fc
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LTC3532
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OPERATIO
88%
DMAX
BOOST
VOUT
1– (150ns • f)
V4 (≈2.05V)
VIN =
V3 (≈1.65V)
The point at which the 4-switch region ends is given by:
A ON, B OFF
BOOST REGION
PWM CD SWITCHES
DMIN
BOOST
DMAX
BUCK
FOUR SWITCH PWM
BUCK/BOOST REGION
V2 (≈1.55V)
D ON, C OFF
PWM AB SWITCHES BUCK REGION
Boost Region (VIN < VOUT)
V1 (≈0.9V)
0%
DUTY
CYCLE
VIN = VOUT(1 – D) = VOUT(1 – 150ns • f) V
3532 F02
INTERNAL
CONTROL
VOLTAGE, VCI
Figure 2. Switch Control vs Internal Control Voltage, VCI
Buck Region (VIN > VOUT)
Switch D is always on and switch C is always off during this mode. When the internal control voltage, VCI, is
above voltage V1, output A begins to switch. During the
off-time of switch A, synchronous switch B turns on for
the remainder of the time. Switches A and B will alternate
like a typical synchronous buck regulator. As the control
voltage increases, the duty cycle of switch A increases
until the maximum duty cycle of the converter in buck
mode reaches DMAX_BUCK, given by:
DMAX_BUCK = 100 – D4SW %
where D4SW = duty cycle % of the 4-switch range.
D4SW = (150ns • f) • 100 %
where f = operating frequency, Hz.
Beyond this point the “4-switch,” or buck/boost region
is reached.
Buck/Boost or 4-Switch (VIN ~ VOUT)
When the internal control voltage, VCI, is above voltage
V2, switch pair AD remain on for duty cycle DMAX_BUCK,
and the switch pair AC begins to phase in. As switch pair
AC phases in, switch pair BD phases out accordingly.
When the VCI voltage reaches the edge of the buck/boost
range, at voltage V3, the AC switch pair completely phase
out the BD pair, and the boost phase begins at duty cycle
D4SW. The input voltage, VIN, where the 4-switch region
begins is given by:
Switch A is always on and switch B is always off during this mode. When the internal control voltage, VCI, is
above voltage V3, switch pair CD will alternately switch
to provide a boosted output voltage. This operation is like
a synchronous boost regulator. The maximum duty cycle
of the converter is limited to 88% typical and is reached
when VCI is above V4.
Burst Mode OPERATION
Burst Mode operation occurs when the IC delivers energy
to the output until it is regulated and then goes into a sleep
mode where the outputs are off and the IC is consuming
only 35μA of quiescent current from VIN. In this mode the
output ripple has a variable frequency component that
depends upon load current, and will typically be about
2% peak-to-peak. Burst Mode operation ripple can be
reduced slightly by using more output capacitance (47μF
or greater). Another method of reducing Burst Mode
operation ripple is to place a small feedforward capacitor
across the upper resistor in the VOUT feedback divider
network (as in Type III compensation). During the period
where the device is delivering energy to the output, the
peak switch current will be equal to 250mA typical and
the inductor current will terminate at zero current for each
cycle. In this mode the typical maximum average output
current is given by:
IOUT(MAX)BURST ≈
0.2 • VIN
A
VOUT + VIN
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LTC3532
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OPERATIO
VIN
VOUT
VIN
VOUT
7
6
7
6
SW1
+
L
A
D
–
4
SW2
B
C
250mA
3
SW1
–
dI ≈ – VOUT
L
dt
+
L
4
SW2
B
0mA
C
3532 F03
T1
5
5
GND
GND
Figure 3. Inductor Charge Cycle During Burst Mode Operation
Note that the peak efficiency during Burst Mode operation
is less than the peak efficiency during fixed frequency
because the part enters full-time 4-switch mode (when
servicing the output) with discontinuous inductor current as illustrated in Figures 3 and 4. During Burst Mode
operation, the control loop is nonlinear and cannot utilize
the control voltage from the error amp to determine the
control mode, therefore full-time 4-switch mode is required
to maintain the buck/boost function. The efficiency below
1mA becomes dominated primarily by the quiescent current. The Burst Mode operation efficiency is given by:
EFFICIENCY ≅
D
n • ILOAD
35μA + ILOAD
where n is typically 88% during Burst Mode operation.
Automatic Burst Mode Operation Control
Burst Mode operation can be automatic or manually controlled with a single pin. In automatic mode, the IC will
enter Burst Mode operation at light load and return to fixed
frequency operation at heavier loads. The load current at
which the mode transition occurs is programmed using
a single external resistor from the BURST pin to ground,
according to the following equations:
Enter Burst Mode Operation: I =
Leave Burst Mode Operation: I =
10.5V
RBURST
7V
RBURST
IINDUCTOR
3
dI ≈ VIN
dt
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IINDUCTOR
A
250mA
0mA
T2
3532 F04
Figure 4. Inductor Disharge Cycle During Burst Mode Operation
where RBURST is in kΩ and IBURST is the load transition
current in Amps. For automatic operation, a filter capacitor should also be connected from BURST to ground to
prevent ripple on BURST from causing the IC to oscillate
in and out of Burst Mode operation. The equation for the
minimum capacitor value is:
CBURST(MIN) ≥
COUT • VOUT
60,000V
where CBURST(MIN) and COUT are in μF. In the event that
a load transient causes the feedback pin to drop by more
than 4% from the regulation value while in Burst Mode
operation, the IC will immediately switch to fixed frequency
mode and an internal pull-up will be momentarily applied
to BURST, rapidly charging the BURST capacitor. This
prevents the IC from immediately reentering Burst Mode
operation once the output achieves regulation.
Manual Burst Mode Operation
For manual control of Burst Mode operation, the RC network connected to BURST can be eliminated. To force fixed
frequency mode, BURST should be connected to VOUT. To
force Burst Mode operation, BURST should be grounded.
When commanding Burst Mode operation manually, the
circuit connected to BURST should be able to sink up to
2mA. For optimum transient response with large dynamic
loads, the operating mode should be controlled manually
by the host. By commanding fixed frequency operation
prior to a sudden increase in load, output voltage droop can
3532fc
9
LTC3532
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OPERATIO
be minimized. Note that if the load current applied during
forced Burst Mode operation (BURST pin is grounded)
exceeds the current that can be supplied, the output voltage
will start to droop and the IC will automatically come out
of Burst Mode operation and enter fixed frequency mode,
raising VOUT. Once regulation is achieved, the IC will then
enter Burst Mode operation once again, and the cycle will
repeat, resulting in about 4% output ripple. Note that Burst
Mode operation is inhibited during soft-start.
incorporates an active clamp circuit that holds the voltage
on VC at an optimal voltage during Burst Mode operation.
This minimizes any output transient when returning to
fixed frequency mode operation. For optimum transient
response, Type 3 compensation is also recommended
to broad band the control loop and roll off past the two
pole response of the output LC filter. (See Closing the
Feedback Loop.)
Burst Mode Operation to Fixed Frequency Transient
Response
The soft-start function is combined with shutdown. When
the SHDN/SS pin is brought above 1V typical, the IC is
enabled but the EA duty cycle is clamped from VC. A detailed diagram of this function is shown in Figure 5. The
components RSS and CSS provide a slow ramping voltage
on SHDN/SS to provide a soft-start function. To ensure
that VC is not being clamped, SHDN/SS must be raised
above 2.4V. To enable Burst Mode operation, SHDN/SS
must be raised to within 0.5V of VIN.
In Burst Mode operation, the compensation network is
not used and VC is disconnected from the error amplifier.
During long periods of Burst Mode operation, leakage
currents in the external components or on the PC board
could cause the compensation capacitor to charge (or
discharge), which could result in a large output transient
when returning to fixed frequency mode of operation, even
at the same load current. To prevent this, the LTC3532
Soft-Start
ERROR AMP
VIN
15μA
+
VOUT
1.22V
R1
FB
–
9
VC
SOFT-START
CLAMP
TO PWM
COMPARATORS
CP1
R2
10
VCI
SHDN/SS
RSS
ENABLE SIGNAL
8
CSS
+
3532 F05
CHIP
ENABLE
–
1V
Figure 5. Soft-Start Circuitry
3532fc
10
LTC3532
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APPLICATIO S I FOR ATIO
1 RT
LTC3532
2 BURST
peak inductor currents in the 1A to 2A region. To minimize
radiated noise, use a shielded inductor. See Table 1 for a
suggested list of inductor suppliers.
VC 10
FB 9
3 SW1
SHDN/SS 8
4 SW2
VIN 7
5 GND
VOUT 6
Table 1. Inductor Vendor Information
GND
3532 F06
Figure 6. Recommended Component Placement. Traces Carrying
High Current are Direct. Trace area at FB and VC Pins are Kept
Low. Lead Length to Battery Should be Kept Short
Inductor Selection
SUPPLIER
WEB SITE
Coilcraft
www.coilcraft.com
Murata
www.murata.com
Sumida
www.sumida.com
TDK
www.component.tdk.com
TOKO
www.tokoam.com
Output Capacitor Selection
The bulk value of the output filter capacitor is set to reduce
the ripple due to charge into the capacitor each cycle. The
steady state ripple due to charge is given by:
The high frequency operation of the LTC3532 allows the
use of small surface mount inductors. The inductor ripple
current is typically set to 20% to 40% of the maximum
inductor current. For a given ripple the inductance terms
are given as follows:
% RIPPLE_BOOST =
VIN(MIN) • (VOUT – VIN(MIN) )
% RIPPLE_BUCK =
LBOOST >
LBUCK >
f • ΔIL • VOUT
VOUT • (VIN(MAX) – VOUT )
f • ΔIL • VIN(MAX)
H
IOUT(MAX) • (VOUT – VIN(MIN) ) • 100
COUT • VOUT 2 • f
%
(VIN(MAX) – VOUT ) • 100%
1
•
VIN(MAX)
8LCf2
H
where f = Operating frequency, Hz
ΔIL = Maximum allowable inductor ripple current, A
VIN(MIN) = Minimum input voltage
VIN(MAX) = Maximum input voltage
VOUT = Output voltage
IOUT(MAX) = Maximum output load current
For high efficiency, choose a ferrite inductor with a high
frequency core material to reduce core losses. The inductor should have low ESR (equivalent series resistance) to
reduce the I2R losses, and must be able to handle the peak
inductor current without saturating. Molded chokes or chip
inductors usually do not have enough core to support the
where COUT = output filter capacitor in Farads and
f = switching frequency in Hz.
The output capacitance is usually many times larger than
the minimum value in order to handle the transient response
requirements of the converter. As a rule of thumb, the ratio
of the operating frequency to the unity-gain bandwidth of
the converter is the amount the output capacitance will
have to increase from the above calculations in order to
maintain the desired transient response.
The other component of ripple is due to the ESR (equivalent series resistance) of the output capacitor. Low ESR
capacitors should be used to minimize output voltage
ripple. For surface mount applications, Taiyo Yuden or
TDK ceramic capacitors, AVX TPS series tantalum capacitors or Sanyo POSCAP are recommended. See Table 2 for
contact information.
3532fc
11
LTC3532
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APPLICATIO S I FOR ATIO
Table 2. Capacitor Vendor Information
Operating Frequency Selection
SUPPLIER
WEB SITE
AVX
www.avxcorp.com
Murata
www.murata.com
Sanyo
www.sanyovideo.com
Taiyo Yuden
www.t-yuden.com
TDK
www.component.tdk.com
Higher operating frequencies allow the use of a smaller
inductor and smaller input and output filter capacitors,
thus reducing board area and component height. However, higher operating frequencies also increase the IC’s
total quiescent current due to the gate charge of the four
switches, as given by:
Input Capacitor Selection
Since VIN is the supply voltage for the IC, as well as the
input to the power stage of the converter, it is recommended
to place at least a 4.7μF, low ESR ceramic bypass capacitor close to the VIN and GND pins. It is also important to
minimize any stray resistance from the converter to the
battery or other power source.
Optional Schottky Diodes
The Schottky diodes across the synchronous switches
B and D are not required (VOUT < 4.3V), but provide a
lower drop during the break-before-make time (typically
15ns) improving efficiency. Use a surface mount Schottky
diode such as an MBRM120T3 or equivalent. Do not use
ordinary rectifier diodes, since the slow recovery times
will compromise efficiency. For applications with an
output voltage above 4.3V, a Schottky diode is required
from SW2 to VOUT.
Output Voltage > 4.3V
A Schottky diode from SW2 to VOUT is required for output
voltages over 4.3V. The diode must be located as close to
the pins as possible in order to reduce the peak voltage on
SW2 due to the parasitic lead and trace inductance.
Input Voltage > 4.5V
For applications with input voltages above 4.5V which
could exhibit an overload or short-circuit condition, a
2Ω/1nF series snubber is required between SW1 and
GND. A Schottky diode from SW1 to VIN should also be
added as close to the pins as possible. For the higher input
voltages, VIN bypassing becomes more critical; therefore,
a ceramic bypass capacitor as close to the VIN and SGND
pins as possible is also required.
Buck: IQ = (0.125 • VIN • f) mA
Boost: IQ = [0.06 • (VIN + VOUT) • f] mA
Buck/Boost: IQ = [f • (0.19 • VIN + 0.06 • VOUT)] mA
where f = switching frequency in MHz. Therefore frequency
selection is a compromise between the optimal efficiency
and the smallest solution size.
Closing the Feedback Loop
The LTC3532 incorporates voltage mode PWM control.
The control to output gain varies with operation region
(buck, boost, buck/boost), but is usually no greater than
15. The output filter exhibits a double pole response, as
given by:
f FILTER — POLE =
1
2 • π • L • COUT
Hz
(in buck mode)
f FILTER — POLE =
VIN
2 • VOUT • π • L • COUT
Hz
(in boost mode)
where L is in henrys and COUT is in farads.
The output filter zero is given by:
f FILTER — ZERO =
1
2 • π • RESR • COUT
Hz
where RESR is the equivalent series resistance of the
output capacitor.
A troublesome feature in boost mode is the right-half plane
zero (RHP), given by:
f RHPZ =
VIN2
Hz
2 • π • IOUT • L • VOUT
3532fc
12
LTC3532
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APPLICATIO S I FOR ATIO
The loop gain is typically rolled off before the RHP zero
frequency.
A simple Type I compensation network can be incorporated to stabilize the loop, but at a cost of reduced bandwidth and slower transient response. To ensure proper
phase margin using Type I compensation, the loop must
be crossed over a decade before the LC double pole.
The unity-gain frequency of the error amplifier with the
Type I compensation is given by:
the output filter. Referring to Figure 8, the location of the
poles and zeros are given by:
fPOLE1 ≅
1
Hz
2 • π • 32e3 • R1• CP1
(which is extremely close to DC)
fZERO1 =
1
Hz
2 • π • RZ • CP1
fZERO2 =
1
Hz
2 • π • R1• CZ1
referring to Figure 7.
fPOLE2 =
Most applications demand an improved transient response
to allow a smaller output filter capacitor. To achieve a higher
bandwidth, Type III compensation is required, providing
two zeros to compensate for the double-pole response of
1
Hz
2 • π • RZ • CP2
where resistance is in ohms and capacitance is in farads.
fUG =
1
Hz
2 • π • R1• CP1
VOUT
+
VOUT
+
ERROR
AMP
–
1.22V
R1
FB
10
–
1.22V
R1
CZ1
FB
9
VC
9
VC
ERROR
AMP
CP1
RZ
R2
10
CP1
R2
CP2
3532 F08
3532 F07
Figure 7. Error Amplifier with Type l Compensation
Figure 8. Error Amplifier with Type lll Compensation
3532fc
13
LTC3532
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TYPICAL APPLICATIO S
Three Cell to 3.3V at 300mA Buck-Boost Converter
With Automatic Burst Mode Operation and Soft-Start
VOUT
3.3V
300mA
L1
4.7μH
SW1
VIN
2.7V TO 4.5V
SHDN
R7
200k
SW2
VIN
VOUT
SHDN/SS
BURST
C4
150pF
VC
VC
RT
R6
12.1k
GND
C2
150pF
0.01μF
C5
4.7nF
200k
R9
1k
FB
FB
LTC3532
BURST
RT
C1
4.7μF
SW1
R1
340k
SW2
C3
22μF
R2
200k
R4
86.6k
3532 TA02
Li-Ion to 5V Boost Converter with Output Disconnect
D1
DMBRM 110LT3
L1
2.2μH
SW1
VIN
2.5V TO 4.2V
SHDN
BURST
VIN
VOUT
BURST
RT
C5
SD
4.7nF
SW2
SHDN/SS
R7
200k
C1
4.7μF
SW1
RT
R4
28.7k
LTC3532
FB
VC
GND
VOUT
5V
300mA
R1
412k
SW2
R9
1k
FB
C4
68pF
VC
R6
12.1k
C2
220pF
C3
10μF
R2
133k
3532 TA03
3532fc
14
LTC3532
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PACKAGE DESCRIPTIO
DD Package
10-Lead Plastic DFN (3mm × 3mm)
(Reference LTC DWG # 05-08-1699)
R = 0.115
TYP
6
0.38 ± 0.10
10
0.675 ±0.05
3.50 ±0.05
1.65 ±0.05
2.15 ±0.05 (2 SIDES)
3.00 ±0.10
(4 SIDES)
PACKAGE
OUTLINE
1.65 ± 0.10
(2 SIDES)
PIN 1
TOP MARK
(SEE NOTE 6)
(DD) DFN 1103
5
0.25 ± 0.05
0.50 BSC
0.75 ±0.05
0.200 REF
0.25 ± 0.05
1
0.50
BSC
2.38 ±0.05
(2 SIDES)
2.38 ±0.10
(2 SIDES)
0.00 – 0.05
BOTTOM VIEW—EXPOSED PAD
RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS
NOTE:
1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT
2. DRAWING NOT TO SCALE
3. ALL DIMENSIONS ARE IN MILLIMETERS
4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE
MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE
5. EXPOSED PAD SHALL BE SOLDER PLATED
6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE
MS Package
10-Lead Plastic MSOP
(Reference LTC DWG # 05-08-1661 Rev E)
3.00 ± 0.102
(.118 ± .004)
(NOTE 3)
0.889 ± 0.127
(.035 ± .005)
5.23
(.206)
MIN
10 9 8 7 6
3.20 – 3.45
(.126 – .136)
0.254
(.010)
3.00 ± 0.102
(.118 ± .004)
(NOTE 4)
4.90 ± 0.152
(.193 ± .006)
DETAIL “A”
0.497 ± 0.076
(.0196 ± .003)
REF
0° – 6° TYP
GAUGE PLANE
0.50
0.305 ± 0.038
(.0197)
(.0120 ± .0015)
BSC
TYP
RECOMMENDED SOLDER PAD LAYOUT
1 2 3 4 5
0.53 ± 0.152
(.021 ± .006)
DETAIL “A”
0.86
(.034)
REF
1.10
(.043)
MAX
0.18
(.007)
SEATING
PLANE
NOTE:
1. DIMENSIONS IN MILLIMETER/(INCH)
2. DRAWING NOT TO SCALE
3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE
5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX
0.17 – 0.27
(.007 – .011)
TYP
0.50
(.0197)
BSC
0.1016 ± 0.0508
(.004 ± .002)
MSOP (MS) 0307 REV E
3532fc
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
15
LTC3532
U
TYPICAL APPLICATIO
Low Profile Li-Ion to 3.3V at 300mA Converter with Automatic Burst Mode Operation
VOUT
3.3V
300mA
L1
2.2μH
SW1
VIN
2.5V TO 4.2V
SW1
SHDN/SS LTC3532
BURST
RT
R3
200k
C1
4.7μF
R9
1k
VOUT
VIN
BURST
SW2
R1
340k
SW2
FB
VC
GND
RT
R4
28.7k
FB
C4
68pF
VC
R6
12.1k
C2
220pF
C3
10μF
R2
200k
C5
0.01μF
L1: COILCRAFT LPO6610-222M
3532 TA04
RELATED PARTS
PART NUMBER
DESCRIPTION
LTC3440
600mA IOUT, 2MHz, Synchronous Buck- VIN: 2.5V to 5.5V, VOUT(RANGE): 2.5V to 5.5V, IQ = 25μA, ISD = <1μA, MS10/DFN Package
Boost DC/DC Converter
COMMENTS
LTC3441
1.2A IOUT, 1MHz, Synchronous BuckBoost DC/DC Converter
VIN: 2.4V to 5.5V, VOUT(RANGE): 2.4V to 5.25V, IQ = 25μA, ISD = <1μA, DFN Package
LTC3442
1.2A IOUT, 2MHz, Synchronous BuckBoost DC/DC Converter
VIN: 2.4V to 5.5V, VOUT(RANGE): 2.4V to 5.25V, IQ = 35μA, ISD = <1μA, DFN Package
LTC3443
1.2A IOUT, 600kHz, Synchronous BuckBoost DC/DC Converter
VIN: 2.4V to 5.5V, VOUT(RANGE): 2.4V to 5.25V, IQ = 28μA, ISD = <1μA, MS10 Package
LTC3444
500mA IOUT, 1.5MHz, Synchronous
VIN: 2.7V to 5.5V, VOUT(RANGE): 0.5V to 5.25V, ISD = <1μA, 3 × 3 DFN Package
Buck-Boost DC/DC Converter Optimized
for WCDMA
LTC3531/
LTC3531-3.3/
LTC3531-3
200mA IOUT, Synchronous Buck-Boost
DC/DC Converters in SOT-23
VIN: 1.8V to 5.5V, VOUT(RANGE): 2V to 5.25V, IQ = 16μA, ISD = <1μA, SOT-23 and 3 × 3 DFN
Packages
3532fc
16
Linear Technology Corporation
LT 0308 REV C • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900 ● FAX: (408) 434-0507
●
www.linear.com
© LINEAR TECHNOLOGY CORPORATION 2006
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