LTM4609
36VIN, 34VOUT High Efficiency
Buck-Boost DC/DC
µModule Regulator
Description
Features
Single Inductor Architecture Allows VIN Above,
Below or Equal to VOUT
n Wide V Range: 4.5V to 36V
IN
n Wide V
OUT Range: 0.8V to 34V
n I
OUT : 4A DC (10A DC in Buck Mode)
n Up to 98% Efficiency
n Current Mode Control
n Power Good Output Signal
n Phase-Lockable Fixed Frequency: 200kHz to 400kHz
n Ultrafast Transient Response
n Current Foldback Protection
n Output Overvoltage Protection
n Small Surface Mount Footprint, Low Profile
(15mm × 15mm × 2.82mm) LGA and
(15mm × 15mm × 3.42mm) BGA Packages
n SnPb (BGA) or RoHS Compliant (LGA and BGA)
Finish
The LTM®4609 is a high efficiency switching mode buckboost power supply. Included in the package are the
switching controller, power FETs and support components.
Operating over an input voltage range of 4.5V to 36V, the
LTM4609 supports an output voltage range of 0.8V to
34V, set by a resistor. This high efficiency design delivers
up to 4A continuous current in boost mode (10A in buck
mode). Only the inductor, sense resistor, bulk input and
output capacitors are needed to finish the design.
n
The low profile package enables utilization of unused space
on the bottom of PC boards for high density point of load
regulation. The high switching frequency and current
mode architecture enable a very fast transient response
to line and load changes without sacrificing stability. The
LTM4609 can be frequency synchronized with an external
clock to reduce undesirable frequency harmonics.
Fault protection features include overvoltage and foldback
current protection. The DC/DC µModule® regulator is offered in small 15mm × 15mm × 2.82mm LGA and 15mm
× 15mm × 3.42mm BGA packages. The LTM4609 is available with SnPb (BGA) or RoHS compliant terminal finish.
Applications
Telecom, Servers and Networking Equipment
Industrial and Automotive Equipment
n High Power Battery-Operated Devices
n
n
L, LT, LTC, LTM, Linear Technology, the Linear logo, µModule, Burst Mode and PolyPhase are
registered trademarks and No RSENSE is a trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
Typical Application
Efficiency and Power Loss
vs Input Voltage
30V/2A Buck-Boost DC/DC µModule Regulator with 6.5V to 36V Input
VIN
RUN
PLLIN V
OUT
FCB
LTM4609
10µF
50V
5.6µH
+
330µF
50V
VOUT
30V
2A
SW1
SW2
RSENSE
SENSE+
0.1µF
SS
SGND
SENSE–
PGND
R2
15mΩ
×2
VFB
98
4609 TA01a
5
97
4
96
95
3
94
2
93
92
91
2.74k
6
POWER LOSS (W)
ON/OFF
99
CLOCK SYNC
10µF
50V
EFFICIENCY (%)
VIN
6.5V TO 36V
EFFICIENCY
POWER LOSS
8
12
16
24
20
VIN (V)
28
32
36
1
0
4609 TA01b
4609ff
For more information www.linear.com/LTM4609
1
LTM4609
Absolute Maximum Ratings
(Note 1)
VIN.............................................................. –0.3V to 36V
VOUT.............................................................. 0.8V to 36V
INTVCC, EXTVCC, RUN, SS, PGOOD............... –0.3V to 7V
SW1, SW2 (Note 7)....................................... –5V to 36V
VFB............................................................. –0.3V to 2.4V
COMP........................................................... –0.3V to 2V
FCB, STBYMD........................................ –0.3V to INTVCC
PLLIN......................................................... –0.3V to 5.5V
Pin Configuration
TOP VIEW
PLLFLTR..................................................... –0.3V to 2.7V
INTVCC................................................................. –40mA
Operating Temperature Range (Note 2)
E- and I-grades.....................................–40°C to 85°C
MP-grade............................................ –55°C to 125°C
Junction Temperature............................................ 125°C
Storage Temperature Range....................–55°C to 125°C
Solder Temperature (Note 3).................................. 245°C
(See Table 6 Pin Assignment)
TOP VIEW
SW2
(BANK 2)
M
M
L
L
SW1
(BANK 4)
VOUT
(BANK 5)
INTVCC
EXTVCC
PGND
(BANK 6)
PGOOD
VFB
SW2
(BANK 2)
VIN
(BANK 1)
K
SW1
(BANK 4)
J
J
H
H
VOUT
(BANK 5)
RSENSE
(BANK 3)
G
INTVCC
EXTVCC
F
F
E
E
D
PGND
(BANK 6)
B
COMP
PLLFLTR
PLLIN
SENSE – SS SGND RUN FCB
A
1
2
3
4
5
6
7
8
9
SENSE+
10
11
PGOOD
VFB
RSENSE
(BANK 3)
G
D
C
VIN
(BANK 1)
K
C
B
COMP
PLLFLTR
PLLIN
SENSE – SS SGND RUN FCB
A
1
12
2
3
4
5
6
7
8
SENSE+
STBYMD
9
10
11
12
STBYMD
BGA PACKAGE
141-LEAD (15mm × 15mm × 3.42mm)
LGA PACKAGE
141-LEAD (15mm × 15mm × 2.82mm)
TJMAX = 125°C, θJA = 11.4°C/W, θJCtop = 15°C/W, θJCbottom = 4°C/W, WEIGHT = 1.7g
TJMAX = 125°C, θJA = 11.4°C/W, θJCtop = 15°C/W, θJCbottom = 4°C/W, WEIGHT = 1.5g
Order Information
PART NUMBER
PAD OR BALL FINISH
PART MARKING*
DEVICE
FINISH CODE
PACKAGE
TYPE
MSL
RATING
TEMPERATURE RANGE
(Note 2)
LTM4609EV#PBF
Au (RoHS)
LTM4609V
e4
LGA
3
–40°C to 85°C
LTM4609IV#PBF
Au (RoHS)
LTM4609V
e4
LGA
3
–40°C to 85°C
LTM4609MPV#PBF
Au (RoHS)
LTM4609V
e4
LGA
3
–55°C to 125°C
LTM4609EY#PBF
SAC305 (RoHS)
LTM4609Y
e1
BGA
3
–40°C to 85°C
LTM4609IY#PBF
SAC305 (RoHS)
LTM4609Y
e1
BGA
3
–40°C to 85°C
LTM4609IY
SnPb (63/37)
LTM4609Y
e0
BGA
3
–40°C to 85°C
LTM4609MPY #PBF
SAC305 (RoHS)
LTM4609Y
e1
BGA
3
–55°C to 125°C
LTM4609MPY
SnPb (63/37)
LTM4609Y
e0
BGA
3
–55°C to 125°C
Consult Marketing for parts specified with wider operating temperature
ranges. *Device temperature grade is indicated by a label on the shipping
container. Pad or ball finish code is per IPC/JEDEC J-STD-609.
• Recommended LGA and BGA PCB Assembly and Manufacturing
Procedures:
www.linear.com/umodule/pcbassembly
• Pb-free and Non-Pb-free Part Markings:
www.linear.com/leadfree
• LGA and BGA Package and Tray Drawings:
www.linear.com/packaging
4609ff
2
For more information www.linear.com/LTM4609
LTM4609
Electrical Characteristics
The l denotes the specifications which apply over the specified operating
temperature range (Note 2), otherwise specifications are at TA = 25°C, VIN = 12V, per typical application (front page) configuration.
SYMBOL
PARAMETER
Input Specifications
VIN(DC)
Input DC Voltage
VIN(UVLO)
Undervoltage Lockout Threshold
IQ(VIN)
CONDITIONS
l
VIN Falling (–40°C to 85°C)
VIN Falling (–55°C to 125°C)
Input Supply Bias Current
Normal
Standby
Shutdown Supply Current
Output Specifications
Output Continuous Current Range
IOUTDC
(Note 3)
Load Regulation Accuracy
VCOMP = 1.2V to 0.7V
VCOMP = 1.2V to 1.8V (Note 4)
Turn-On Time
M3 tf
Turn-Off Time
M2, M4 tr
Turn-On Time
M2, M4 tf
Turn-Off Time
t1d
M1 Off to M2 On Delay
t2d
M2 Off to M1 On Delay
t3d
M3 Off to M4 On Delay
t4d
M4 Off to M3 On Delay
Mode Transition 1
M2 Off to M4 On Delay
Mode Transition 2
M4 Off to M2 On Delay
M1 RDS(ON)
Static Drain-to-Source
On-Resistance
Static Drain-to-Source
M2 RDS(ON)
On-Resistance
Static Drain-to-Source
M3 RDS(ON)
On-Resistance
Static Drain-to-Source
M4 RDS(ON)
On-Resistance
Oscillator and Phase-Locked Loop
fNOM
Nominal Frequency
fLOW
Lowest Frequency
36
4
4.5
V
V
V
60
mA
mA
µA
10
4
ΔVFB/VFB(LOAD)
M3 tr
3.4
3.4
4.5
l
l
VIN = 32V, VOUT = 12V
VIN = 6V, VOUT = 12V
VIN = 4.5V to 36V, VCOMP = 1.2V (Note 4)
Turn-Off Time
MAX
2.8
1.6
35
Line Regulation Accuracy
M1 tf
TYP
VRUN = 0V, VSTBYMD > 2V
VRUN = 0V, VSTBYMD = Open
ΔVFB/VFB(NOM)
Switch Section (Note 5)
M1 tr
Turn-On Time
MIN
l
l
Drain to Source Voltage VDS = 12V,
Bias Current ISW = 10mA
Drain to Source Voltage VDS = 12V,
Bias Current ISW = 10mA
Drain to Source Voltage VDS = 12V,
Bias Current ISW = 10mA
Drain to Source Voltage VDS = 12V,
Bias Current ISW = 10mA
Drain to Source Voltage VDS = 12V,
Bias Current ISW = 10mA
Drain to Source Voltage VDS = 12V,
Bias Current ISW = 10mA
Drain to Source Voltage VDS = 12V,
Bias Current ISW = 10mA
Drain to Source Voltage VDS = 12V,
Bias Current ISW = 10mA
Drain to Source Voltage VDS = 12V,
Bias Current ISW = 10mA
Drain to Source Voltage VDS = 12V,
Bias Current ISW = 10mA
Drain to Source Voltage VDS = 12V,
Bias Current ISW = 10mA
Drain to Source Voltage VDS = 12V,
Bias Current ISW = 10mA
Bias Current ISW = 3A
UNITS
A
A
0.002
0.02
%/V
0.15
–0.15
0.5
–0.5
%
%
50
ns
40
ns
25
ns
20
ns
20
ns
20
ns
50
ns
50
ns
50
ns
50
ns
220
ns
220
ns
10
mΩ
Bias Current ISW = 3A
14
20
mΩ
Bias Current ISW = 3A
14
20
mΩ
Bias Current ISW = 3A
14
20
mΩ
300
200
330
220
kHz
kHz
VPLLFLTR = 1.2V
VPLLFLTR = 0V
260
170
4609ff
For more information www.linear.com/LTM4609
3
LTM4609
Electrical
Characteristics
The
l denotes the specifications which apply over the specified operating
temperature range (Note 2), otherwise specifications are at TA = 25°C, VIN = 12V, per typical application (front page) configuration.
SYMBOL
fHIGH
RPLLIN
IPLLFLTR
PARAMETER
Highest Frequency
PLLIN Input Resistance
Phase Detector Output Current
CONDITIONS
VPLLFLTR = 2.4V
Control Section
VFB
Feedback Reference Voltage
VCOMP = 1.2V(–40°C to 85°C)
VCOMP = 1.2V (–55°C to 125°C)
TYP
400
50
–15
15
MAX
440
UNITS
kHz
kΩ
µA
µA
0.792
0.785
1
0.8
0.8
1.6
–1.7
0.7
1.25
0.8
–0.2
5.3
0.808
0.815
2.2
–1
0.84
–0.1
5.5
V
V
V
µA
V
V
V
µA
V
99
99
200
250
%
%
ns
99.5
100
100.5
kΩ
l
l
5.7
5.56
6.3
6.35
2
l
5.4
6
6
0.3
5.6
300
60
V
V
%
V
mV
mV
160
–130
–6
–380
190
–150
mV
mV
mV
µA
7.5
–7.5
2.5
0.2
10
–10
%
%
%
V
µA
fPLLIN < fOSC
fPLLIN > fOSC
RUN Pin ON/OFF Threshold
Soft-Start Charging Current
Start-Up Threshold
Keep-Active Power On Threshold
Forced Continuous Threshold
Forced Continuous Pin Current
Burst Inhibit (Constant Frequency)
Threshold
Maximum Duty Factor
DF(BOOST, MAX)
DF(BUCK, MAX)
Maximum Duty Factor
tON(MIN, BUCK)
Minimum On-Time for Synchronous
Switch in Buck Operation
RFBHI
Resistor Between VOUT and VFB Pins
Internal VCC Regulator
INTVCC
Internal VCC Voltage
VRUN
ISS
VSTBYMD(START)
VSTBYMD(KA)
VFCB
IFCB
VBURST
Internal VCC Load Regulation
ΔVLDO/VLDO
VEXTVCC
EXTVCC Switchover Voltage
EXTVCC Switchover Hysteresis
ΔVEXTVCC(HYS)
EXTVCC Switch Drop Voltage
ΔVEXTVCC
Current Sensing Section
VSENSE(MAX)
Maximum Current Sense Threshold
VSENSE(MIN, BUCK)
ISENSE
PGOOD
ΔVFBH
ΔVFBL
ΔVFB(HYS)
VPGL
IPGOOD
MIN
340
l
l
VRUN = 2.2V
VSTBYMD Rising
VSTBYMD Rising, VRUN = 0V
0.4
0.76
–0.3
VFCB = 0.85V
Measured at FCB Pin
% Switch M4 On
% Switch M1 On
Switch M1 (Note 6)
VIN = 12V, VEXTVCC = 5V
VIN = 7V, VEXTVCC = 5V
ICC = 0mA to 20mA, VEXTVCC = 5V
ICC = 20mA, VEXTVCC Rising
ICC = 20mA, VEXTVCC = 6V
Minimum Current Sense Threshold
Sense Pins Total Source Current
Boost Mode
Buck Mode
Discontinuous Mode
VSENSE– = VSENSE+ = 0V
PGOOD Upper Threshold
PGOOD Lower Threshold
PGOOD Hysteresis
PGOOD Low Voltage
PGOOD Leakage Current
VFB Rising
VFB Falling
VFB Returning
IPGOOD = 2mA
VPGOOD = 5V
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 LTM4609 is tested under pulsed load conditions such that
TJ ≈ TA. The LTM4609E 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. The LTM4609I is guaranteed over
the –40°C to 85°C operating temperature range. The LTM4609MP is
guaranteed and tested over the –55°C to 125°C operating temperature
l
l
–95
5.5
–5.5
150
0.3
1
range. For output current derating at high temperature, please refer to
Thermal Considerations and Output Current Derating discussion.
Note 3: See output current derating curves for different VIN, VOUT, and TA.
Note 4: The LTM4609 is tested in a feedback loop that servos VCOMP to a
specified voltage and measures the resultant VFB.
Note 5: Turn-on and turn-off time are measured using 10% and 90%
levels. Transition delay time is measured using 50% levels.
Note 6: 100% test at wafer level only.
Note 7: Absolute Maximum Rating of –5V on SW1 and SW2 is under
transient condition only.
4609ff
4
For more information www.linear.com/LTM4609
LTM4609
Typical Performance Characteristics
100
Efficiency vs Load Current
12VIN to 12VOUT
Efficiency vs Load Current
32VIN to 12VOUT
100
90
90
80
80
80
70
70
70
60
50
40
30
20
0
0.01
0.1
1
LOAD CURRENT (A)
60
50
40
30
0
0.01
0.1
1
LOAD CURRENT (A)
4609 G01
0
0.01
10
100
99
70
99
98
1
2
3 4 5 6 7
LOAD CURRENT (A)
8
9
96
95
94
93
28VIN to 20VOUT
32VIN to 20VOUT
36VIN to 20VOUT
91
10
90
0
1
2
4
5
3
6
LOAD CURRENT (A)
96
7
Efficiency vs Load Current
3.3µH Inductor
8
93
0
1
3
2
4
LOAD CURRENT (A)
100
6
5
4609 G06
Transient Response from
12VIN to 12VOUT
Transient Response from
6VIN to 12VOUT
95
30VIN to 30VOUT
32VIN to 30VOUT
36VIN to 30VOUT
94
4609 G05
4609 G04
EFFICIENCY (%)
97
95
92
12VIN TO 5VOUT
24VIN TO 5VOUT
32VIN TO 5VOUT
0
98
97
EFFICIENCY (%)
EFFICIENCY (%)
EFFICIENCY (%)
95
80
100
Efficiency vs Load Current
8µH Inductor
100
100
85
0.1
1
10
LOAD CURRENT (A)
4609 G03
Efficiency vs Load Current
5.6µH Inductor
90
SKIP CYCLE
DCM
CCM
10
4609 G02
Efficiency vs Load Current
3.3µH Inductor
75
50
40
20
BURST
DCM
CCM
10
10
60
30
20
BURST
DCM
CCM
10
EFFICIENCY (%)
90
EFFICIENCY (%)
EFFICIENCY (%)
100
Efficiency vs Load Current
6VIN to 12VOUT
(Refer to Figure 18)
IOUT
2A/DIV
IOUT
2A/DIV
VOUT
200mV/DIV
VOUT
200mV/DIV
90
85
80
200µs/DIV
70
LOAD STEP: 0A TO 3A AT CCM
OUTPUT CAPS: 4x 22µF CERAMIC CAPS AND
2x 180µF ELECTROLYTIC CAPS
2x 15mΩ SENSING RESISTORS
5VIN to 16VOUT
5VIN to 24VOUT
5VIN to 30VOUT
75
0
0.5
1.5
1
2
LOAD CURRENT (A)
2.5
4609 G08
200µs/DIV
4609 G09
LOAD STEP: 0A TO 3A AT CCM
OUTPUT CAPS: 4x 22µF CERAMIC CAPS AND
2x 180µF ELECTROLYTIC CAPS
2x 15mΩ SENSING RESISTORS
3
4609 G07
4609ff
For more information www.linear.com/LTM4609
5
LTM4609
Typical Performance Characteristics
Transient Response from
32VIN to 12VOUT
Start-Up with 6VIN to 12VOUT at
IOUT = 4A
IOUT
2A/DIV
VOUT
100mV/DIV
200µs/DIV
Start-Up with 32VIN to 12VOUT at
IOUT = 5A
IL
5A/DIV
IL
5A/DIV
IIN
5A/DIV
IIN
2A/DIV
VOUT
10V/DIV
VOUT
10V/DIV
4609 G10
50ms/DIV
4609 G11
10ms/DIV
4609 G12
LOAD STEP: 0A TO 5A AT CCM
OUTPUT CAPS: 4x 22µF CERAMIC CAPS AND
2x 180µF ELECTROLYTIC CAPS
2x 12mΩ SENSING RESISTORS
0.1µF SOFT-START CAP
OUTPUT CAPS: 4x 22µF CERAMIC CAPS AND
2x 180µF ELECTROLYTIC CAPS
2x 12mΩ SENSING RESISTORS
0.1µF SOFT-START CAP
OUTPUT CAPS: 4x 22µF CERAMIC CAPS AND
2x 180µF ELECTROLYTIC CAPS
2x 12mΩ SENSING RESISTORS
Short Circuit with 6VIN to 12VOUT
at IOUT = 4A
Short Circuit with 32VIN to 12VOUT
at IOUT = 5A
Short Circuit with 12VIN to 34VOUT
at IOUT = 2A
VOUT
10V/DIV
VOUT
5V/DIV
IIN
2A/DIV
VOUT
5V/DIV
IIN
5A/DIV
50µs/DIV
4609 G13
OUTPUT CAPS: 4x 22µF CERAMIC CAPS AND
2x 180µF ELECTROLYTIC CAPS
2x 12mΩ SENSING RESISTORS
IIN
5A/DIV
50µs/DIV
4609 G14
OUTPUT CAPS: 4x 22µF CERAMIC CAPS AND
2x 180µF ELECTROLYTIC CAPS
2x 12mΩ SENSING RESISTORS
20µs/DIV
4607 G15
OUTPUT CAPS: 2x 10µF 50V CERAMIC CAPS AND
2x 47µF 50V ELECTROLYTIC CAPS
2x 15mΩ SENSING RESISTORS
4609ff
6
For more information www.linear.com/LTM4609
LTM4609
Pin Functions
VIN (Bank 1): Power Input Pins. Apply input voltage between these pins and PGND pins. Recommend placing
input decoupling capacitance directly between VIN pins
and PGND pins.
VOUT (Bank 5): Power Output Pins. Apply output load
between these pins and PGND pins. Recommend placing
output decoupling capacitance directly between these pins
and PGND pins.
PGND (Bank 6): Power Ground Pins for Both Input and
Output Returns.
SW1, SW2 (Bank 4, Bank 2): Switch Nodes. The power
inductor is connected between SW1 and SW2.
RSENSE (Bank 3): Sensing Resistor Pin. The sensing resistor is connected from this pin to PGND.
SENSE+ (Pin A4): Positive Input to the Current Sense and
Reverse Current Detect Comparators.
SENSE– (Pin A5): Negative Input to the Current Sense and
Reverse Current Detect Comparators.
EXTVCC (Pin F6): External VCC Input. When EXTVCC exceeds
5.7V, an internal switch connects this pin to INTVCC and
shuts down the internal regulator so that the controller and
gate drive power is drawn from EXTVCC. Do not exceed
7V at this pin and ensure that EXTVCC < VIN
INTVCC (Pin F5): Internal 6V Regulator Output. This pin
is for additional decoupling of the 6V internal regulator.
Do not source more than 40mA from INTVCC.
PLLIN (Pin B9): External Clock Synchronization Input
to the Phase Detector. This pin is internally terminated
to SGND with a 50k resistor. The phase-locked loop will
force the rising bottom gate signal of the controller to be
synchronized with the rising edge of PLLIN signal.
PLLFLTR (Pin B8): The lowpass filter of the phase-locked
loop is tied to this pin. This pin can also be used to set the
frequency of the internal oscillator with an AC or DC voltage. See the Applications Information section for details.
SS (Pin A6): Soft-Start Pin. Soft-start reduces the input
surge current from the power source by gradually increasing the controller’s current limit.
STBYMD (Pin A10): LDO Control Pin. Determines whether
the internal LDO remains active when the controller is shut
down. See Operations section for details. If the STBYMD
pin is pulled to ground, the SS pin is internally pulled to
ground to disable start-up and thereby providing a single
control pin for turning off the controller. An internal decoupling capacitor is tied to this pin.
VFB (Pin B6): The Negative Input of the Error Amplifier.
Internally, this pin is connected to VOUT with a 100k precision resistor. Different output voltages can be programmed
with an additional resistor between VFB and SGND pins.
See the Applications Information section.
FCB (Pin A9): Forced Continuous Control Input. The voltage
applied to this pin sets the operating mode of the module.
When the applied voltage is less than 0.8V, the forced
continuous current mode is active in boost operation and
the skip cycle mode is active in buck operation. When the
pin is tied to INTVCC, the constant frequency discontinuous
current mode is active in buck or boost operation. See the
Applications Information section.
SGND (Pin A7): Signal Ground Pin. This pin connects to
PGND at output capacitor point.
COMP (Pin B7): Current Control Threshold and Error
Amplifier Compensation Point. The current comparator
threshold increases with this control voltage. The voltage
ranges from 0V to 2.4V.
PGOOD (Pin B5): Output Voltage Power Good Indicator.
Open drain logic output that is pulled to ground when the
output voltage is not within ±7.5% of the regulation point.
RUN (Pin A8): Run Control Pin. A voltage below 1.6V will
turn off the module. There is a 100k resistor between the
RUN pin and SGND in the module. Do not apply more than
6V to this pin. See the Applications Information section.
4609ff
For more information www.linear.com/LTM4609
7
LTM4609
Simplified Block Diagram
VIN
4.5V TO 36V
EXTVCC
C1
CIN
M1
SW2
INTVCC
M2
PGOOD
L
SW1
RUN
ON/OFF
VOUT
100k
STBYMD
12V
4A
CO1
M3
COUT
0.1µF
100k
COMP
VFB
M4
CONTROLLER
INT
COMP
RFB
7.15k
RSENSE
SENSE+
SS
SS
0.1µF
PLLIN
INT
FILTER
PLLFLTR
RSENSE
SENSE–
PGND
INT
FILTER
FCB
SGND
1000pF
TO PGND PLANE AS
SHOWN IN FIGURE 15
4609 BD
Figure 1. Simplified LTM4609 Block Diagram
Decoupling Requirements
TA = 25°C. Use Figure 1 configuration.
SYMBOL
PARAMETER
CONDITIONS
CIN
External Input Capacitor Requirement
(VIN = 4.5V to 36V, VOUT = 12V)
IOUT = 4A
10
COUT
External Output Capacitor Requirement
(VIN = 4.5V to 36V, VOUT = 12V)
IOUT = 4A
200
MIN
TYP
MAX
UNITS
µF
300
µF
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LTM4609
Operation
Power Module Description
The LTM4609 is a non-isolated buck-boost DC/DC power
supply. It can deliver a wide range output voltage from 0.8V
to 34V over a wide input range from 4.5V to 36V, by only
adding the sensing resistor, inductor and some external
input and output capacitors. It provides precisely regulated
output voltage programmable via one external resistor.
The typical application schematic is shown in Figure 18.
The LTM4609 has an integrated current mode buck-boost
controller, ultralow RDS(ON) FETs with fast switching speed
and integrated Schottky diodes. With current mode control
and internal feedback loop compensation, the LTM4609
module has sufficient stability margins and good transient
performance under a wide range of operating conditions
and with a wide range of output capacitors. The operating
frequency of the LTM4609 can be adjusted from 200kHz
to 400kHz by setting the voltage on the PLLFLTR pin.
Alternatively, its frequency can be synchronized by the
input clock signal from the PLLIN pin. The typical switching frequency is 400kHz.
The Burst Mode® and skip-cycle mode operations can be
enabled at light loads to improve efficiency, while the forced
continuous mode and discontinuous mode operations are
used for constant frequency applications. Foldback current
limiting is activated in an overcurrent condition as VFB
drops. Internal overvoltage and undervoltage comparators pull the open-drain PGOOD output low if the output
feedback voltage exits the ±7.5% window around the
regulation point. Pulling the RUN pin below 1.6V forces
the controller into its shutdown state.
If an external bias supply is applied on the EXTVCC pin, then
an efficiency improvement will occur due to the reduced
power loss in the internal linear regulator. This is especially
true at the higher end of the input voltage range.
Applications Information
The typical LTM4609 application circuit is shown in Figure 18. External component selection is primarily determined by the maximum load current and output voltage.
Refer to Table 3 for specific external capacitor requirements
for a particular application.
Output Voltage Programming
The PWM controller has an internal 0.8V reference voltage.
As shown in the Block Diagram, a 100k internal feedback
resistor connects VOUT and VFB pins together. Adding a
resistor RFB from the VFB pin to the SGND pin programs
the output voltage:
VOUT = 0.8V •
100k +RFB
RFB
Operation Frequency Selection
The LTM4609 uses current mode control architecture at
constant switching frequency, which is determined by the
internal oscillator’s capacitor. This internal capacitor is
charged by a fixed current plus an additional current that
is proportional to the voltage applied to the PLLFLTR pin.
The PLLFLTR pin can be grounded to lower the frequency
to 200kHz or tied to 2.4V to yield approximately 400kHz.
When PLLFLTR is left open, the PLLFLTR pin goes low,
forcing the oscillator to its minimum frequency.
A graph for the voltage applied to the PLLFLTR pin vs
frequency is given in Figure 2. As the operating frequency
increases, the gate charge losses will be higher, thus the
efficiency is lower. The maximum switching frequency is
approximately 400kHz.
Table 1. RFB Resistor (0.5%) vs Output Voltage
VOUT
0.8V
1.5V
2.5V
3.3V
5V
6V
8V
9V
RFB
Open
115k
47.5k
32.4k
19.1k
15.4k
11k
9.76k
VOUT
10V
12V
15V
16V
20V
24V
30V
34V
5.23k
4.12k
3.4k
2.74k
2.37k
RFB
8.66k 7.15k 5.62k
Frequency Synchronization
The LTM4609 can also be synchronized to an external
source via the PLLIN pin instead of adjusting the voltage
on the PLLFLTR pin directly. The power module has a
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9
LTM4609
Applications Information
phase-locked loop comprised of an internal voltage controlled oscillator and a phase detector. This allows turning
on the internal top MOSFET for locking to the rising edge of
the external clock. A pulse detection circuit is used to detect
a clock on the PLLIN pin to turn on the phase-locked loop.
The input pulse width of the clock has to be at least 400ns,
and 2V in amplitude. The synchronized frequency ranges
from 200kHz to 400kHz, corresponding to a DC voltage
input from 0V to 2.4V at PLLFLTR. During the start-up of
the regulator, the phase-locked loop function is disabled.
450
OPERATING FREQUENCY (kHz)
400
350
300
250
200
150
100
50
0
0
1.0
1.5
2.0
0.5
PLLFLTR PIN VOLTAGE (V)
2.5
4609 F02
Figure 2. Frequency vs PLLFLTR Pin Voltage
Low Current Operation
To improve efficiency at low output current operation,
LTM4609 provides three modes for both buck and boost
operations by accepting a logic input on the FCB pin. Table
2 shows the different operation modes.
load current is lower than the preset minimum output
current level. The MOSFETs will turn on for several cycles,
followed by a variable “sleep” interval depending upon the
load current. During buck operation, skip-cycle mode sets
a minimum positive inductor current level. In this mode,
some cycles will be skipped when the output load current
drops below 1% of the maximum designed load in order
to maintain the output voltage.
When the FCB pin voltage is tied to the INTVCC pin, the
controller enters constant frequency discontinuous current
mode (DCM). For boost operation, if the output voltage is
high enough, the controller can enter the continuous current
buck mode for one cycle to discharge inductor current.
In the following cycle, the controller will resume DCM
boost operation. For buck operation, constant frequency
discontinuous current mode is turned on if the preset
minimum negative inductor current level is reached. At
very light loads, this constant frequency operation is not
as efficient as Burst Mode operation or skip-cycle, but
does provide low noise, constant frequency operation.
Input Capacitors
In boost mode, since the input current is continuous, only
minimum input capacitors are required. However, the input
current is discontinuous in buck mode. So the selection
of input capacitor CIN is driven by the need of filtering the
input square wave current.
For a buck converter, the switching duty-cycle can be
estimated as:
Table 2. Different Operating Modes (VINTVCC = 6V)
FCB PIN
BUCK
BOOST
0V to 0.75V
Force Continuous Mode
Force Continuous Mode
0.85V to
VINTVCC – 1V
Skip-Cycle Mode
Burst Mode Operation
>5.3V
DCM with Constant Freq
DCM with Constant Freq
When the FCB pin voltage is lower than 0.8V, the controller
behaves as a continuous, PWM current mode synchronous
switching regulator. When the FCB pin voltage is below
VINTVCC – 1V, but greater than 0.85V, where VINTVCC is 6V,
the controller enters Burst Mode operation in boost operation or enters skip-cycle mode in buck operation. During
boost operation, Burst Mode operation is activated if the
D=
VOUT
VIN
Without considering the inductor current ripple, the RMS
current of the input capacitor can be estimated as:
ICIN(RMS) =
IOUT(MAX)
η
• D•(1-D)
In the above equation, η is the estimated efficiency of the
power module. CIN can be a switcher-rated electrolytic
aluminum capacitor, OS-CON capacitor or high volume
ceramic capacitors. Note the capacitor ripple current
ratings are often based on temperature and hours of life.
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LTM4609
Applications Information
This makes it advisable to properly derate the input capacitor, or choose a capacitor rated at a higher temperature
than required. Always contact the capacitor manufacturer
for derating requirements.
LBOOST ≥
Output Capacitors
In boost mode, the discontinuous current shifts from the
input to the output, so the output capacitor COUT must be
capable of reducing the output voltage ripple.
For boost and buck modes, the steady ripple due to charging and discharging the bulk capacitance is given by:
VRIPPLE,BOOST =
VRIPPLE,BUCK =
ripple ΔIL is typically set to 20% to 40% of the maximum
inductor current. In the inductor design, the worst cases
in continuous mode are considered as follows:
(
IOUT(MAX) • VOUT – VIN(MIN)
COUT • VOUT • ƒ
(
VOUT • VIN(MAX) – VOUT
)
)
8 •L •COUT • VIN(MAX) • ƒ 2
The steady ripple due to the voltage drop across the ESR
(effective series resistance) is given by:
VESR,BUCK = ∆IL(MAX) •ESR
VESR,BOOST =IL(MAX) •ESR
The LTM4609 is designed for low output voltage ripple.
The bulk output capacitors defined as COUT are chosen
with low enough ESR to meet the output voltage ripple and
transient requirements. COUT can be the low ESR tantalum
capacitor, the low ESR polymer capacitor or the ceramic
capacitor. Multiple capacitors can be placed in parallel to
meet the ESR and RMS current handling requirements. The
typical capacitance is 300µF. Additional output filtering may
be required by the system designer, if further reduction of
output ripple or dynamic transient spike is required. Table 3
shows a matrix of different output voltages and output
capacitors to minimize the voltage droop and overshoot
at a current transient.
)
V 2OUT(MAX) • ƒ •IOUT(MAX) •Ripple%
(
VOUT • VIN(MAX) – VOUT
)
VIN(MAX) • ƒ •IOUT(MAX) •Ripple%
where:
ƒ is operating frequency, Hz
Ripple% is allowable inductor current ripple, %
VOUT(MAX) is maximum output voltage, V
VIN(MAX) is maximum input voltage, V
VOUT is output voltage, V
IOUT(MAX) is maximum output load current, A
The inductor should have low DC resistance to reduce the
I2R losses, and must be able to handle the peak inductor
current without saturation. To minimize radiated noise,
use a toroid, pot core or shielded bobbin inductor. Please
refer to Table 3 for the recommended inductors for different cases.
RSENSE Selection and Maximum Output Current
RSENSE is chosen based on the required inductor current.
Since the maximum inductor valley current at buck mode
is much lower than the inductor peak current at boost
mode, different sensing resistors are suggested to use
in buck and boost modes.
The current comparator threshold sets the peak of the
inductor current in boost mode and the maximum inductor
valley current in buck mode. In boost mode, the allowed
maximum average load current is:
Inductor Selection
The inductor is chiefly decided by the required ripple current and the operating frequency. The inductor current
LBUCK ≥
(
V 2IN • VOUT(MAX) – VIN
160mV ∆IL VIN
IOUT(MAX,BOOST) =
–
•
2 VOUT
RSENSE
where ΔIL is peak-to-peak inductor ripple current.
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LTM4609
Applications Information
In buck mode, the allowed maximum average load current is:
130mV ∆IL
IOUT(MAX,BUCK) =
+
R
2
SENSE
The maximum current sensing RSENSE value for the boost
mode is:
RSENSE(MAX,BOOST) =
2 •130mV
2 •IOUT(MAX,BUCK) – ∆IL
A 20% to 30% margin on the calculated sensing resistor
is usually recommended. Please refer to Table 3 for the
recommended sensing resistors for different applications.
Soft-Start
The SS pin provides a means to soft-start the regulator.
A capacitor on this pin will program the ramp rate of the
output voltage. A 1.7µA current source will charge up the
external soft-start capacitor. This will control the ramp of
the internal reference and the output voltage. The total
soft-start time can be calculated as:
tSOFTSTART =
The RUN pin can also be used as an undervoltage lockout
(UVLO) function by connecting a resistor from the input
supply to the RUN pin. The equation:
V_UVLO=
R1+R2
•1.6V
R2
Power Good
The maximum current sensing RSENSE value for the buck
mode is:
The RUN pin is used to enable the power module. The pin
can be driven with a logic input, not to exceed 6V.
2 •160mV • VIN
2 •IOUT(MAX,BOOST) • VOUT + ∆IL • VIN
RSENSE(MAX,BUCK) =
Run Enable
2.4V •CSS
1.7µA
When the RUN pin falls below 1.6V, then the soft-start
pin is reset to allow for proper soft-start control when
the regulator is enabled again. Current foldback and force
continuous mode are disabled during the soft-start process.
Do not apply more than 6V to the SS pin.
The PGOOD pin is an open drain pin that can be used to
monitor valid output voltage regulation. This pin monitors
a ±7.5% window around the regulation point.
COMP Pin
This pin is the external compensation pin. The module
has already been internally compensated for most output
voltages. A spice model is available for other control loop
optimization.
Fault Conditions: Current Limit and Overcurrent
Foldback
LTM4609 has a current mode controller, which inherently
limits the cycle-by-cycle inductor current not only in steady
state operation, but also in transient. Refer to Table 3.
To further limit current in the event of an overload condition, the LTM4609 provides foldback current limiting. If the
output voltage falls by more than 70%, then the maximum
output current is progressively lowered to about 30% of
its full current limit value for boost mode and about 40%
for buck mode.
Standby Mode (STBYMD)
The standby mode (STBYMD) pin provides several choices
for start-up and standby operational modes. If the pin is
pulled to ground, the SS pin is internally pulled to ground,
preventing start-up and thereby providing a single control
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LTM4609
Applications Information
pin for turning off the controller. If the pin is left open or
decoupled with a capacitor to ground, the SS pin is internally
provided with a starting current, permitting external control
for turning on the controller. If the pin is connected to a
voltage greater than 1.25V, the internal regulator (INTVCC)
will be on even when the controller is shut down (RUN
pin voltage
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