TI LM2737 Lm2727/lm2737 n-channel fet synchronous buck regulator controller for low output voltage Datasheet

LM2727, LM2737
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SNVS205D – AUGUST 2002 – REVISED MARCH 2013
LM2727/LM2737 N-Channel FET Synchronous Buck Regulator Controller for Low Output
Voltages
Check for Samples: LM2727, LM2737
FEATURES
DESCRIPTION
•
•
•
The LM2727 and LM2737 are high-speed,
synchronous, switching regulator controllers. They
are intended to control currents of 0.7A to 20A with
up to 95% conversion efficiencies. The LM2727
employs output over-voltage and under-voltage latchoff. For applications where latch-off is not desired, the
LM2737 can be used. Power up and down
sequencing is achieved with the power-good flag,
adjustable soft-start and output enable features. The
LM2737 and LM2737 operate from a low-current 5V
bias and can convert from a 2.2V to 16V power rail.
Both parts utilize a fixed-frequency, voltage-mode,
PWM control architecture and the switching
frequency is adjustable from 50kHz to 2MHz by
adjusting the value of an external resistor. Current
limit is achieved by monitoring the voltage drop
across the on-resistance of the low-side MOSFET,
which enhances low duty-cycle operation. The wide
range of operating frequencies gives the power
supply designer the flexibility to fine-tune component
size, cost, noise and efficiency. The adaptive, nonoverlapping MOSFET gate-drivers and high-side
bootstrap structure helps to further maximize
efficiency. The high-side power FET drain voltage can
be from 2.2V to 16V and the output voltage is
adjustable down to 0.6V.
1
2
•
•
•
•
•
•
•
Input Power from 2.2V to 16V
Output Voltage Adjustable Down to 0.6V
Power Good flag, Adjustable Soft-Start and
Output Enable for Easy Power Sequencing
Output Over-Voltage and Under-Voltage LatchOff (LM2727)
Output Over-Voltage and Under-Voltage Flag
(LM2737)
Reference Accuracy: 1.5% (0°C - 125°C)
Current Limit Without Sense Resistor
Soft Start
Switching Frequency from 50 kHz to 2 MHz
TSSOP-14 Package
APPLICATIONS
•
•
•
•
•
Cable Modems
Set-Top Boxes/ Home Gateways
DDR Core Power
High-Efficiency Distributed Power
Local Regulation of Core Power
Typical Application
+5V
0.1P
RIN
10:
CIN
2.2PF
RFADJ
Q1
VCC
HG
BOOT
SD
CSS
12n
CIN1,2
10PF
6.3V
Si4884DY
1.5 PH
6.1 A, 9.6 m:
RCS
VO = 1.2V@5A
ISEN
PWGD
LM27x7
FREQ
63.4k
VIN = 3.3V
CBOOT
D1
LG
SS
PGND
SGND
PGND
EAO
2.2k
Q2
L1
Si4884DY
RFB2
10k
+
CO1,2
2200PF
6.3V, 2.8A
FB
RFB1
10k
CC1
CC2
180p
2.2p
RC1
392k
1
2
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
All trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2002–2013, Texas Instruments Incorporated
LM2727, LM2737
SNVS205D – AUGUST 2002 – REVISED MARCH 2013
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Connection Diagram
1
2
3
5
6
7
HG
LG
PGND
SGND
Vcc
PWGD
ISEN
PGND
LM27x7
4
BOOT
SD
FREQ
FB
SS
EAO
14
13
12
11
10
9
8
Figure 1. 14-Lead Plastic TSSOP
θJA = 155°C/W
See Package Number PW0014A
PIN DESCRIPTION
BOOT (Pin 1) - Supply rail for the N-channel MOSFET gate drive. The voltage should be at least one gate threshold above the regulator
input voltage to properly turn on the high-side N-FET.
LG (Pin 2) - Gate drive for the low-side N-channel MOSFET. This signal is interlocked with HG to avoid shoot-through problems.
PGND (Pins 3, 13) - Ground for FET drive circuitry. It should be connected to system ground.
SGND (Pin 4) - Ground for signal level circuitry. It should be connected to system ground.
VCC (Pin 5) - Supply rail for the controller.
PWGD (Pin 6) - Power Good. This is an open drain output. The pin is pulled low when the chip is in UVP, OVP, or UVLO mode. During
normal operation, this pin is connected to VCC or other voltage source through a pull-up resistor.
ISEN (Pin 7) - Current limit threshold setting. This sources a fixed 50µA current. A resistor of appropriate value should be connected
between this pin and the drain of the low-side FET.
EAO (Pin 8) - Output of the error amplifier. The voltage level on this pin is compared with an internally generated ramp signal to determine
the duty cycle. This pin is necessary for compensating the control loop.
SS (Pin 9) - Soft start pin. A capacitor connected between this pin and ground sets the speed at which the output voltage ramps up. Larger
capacitor value results in slower output voltage ramp but also lower inrush current.
FB (Pin 10) - This is the inverting input of the error amplifier, which is used for sensing the output voltage and compensating the control
loop.
FREQ (Pin 11) - The switching frequency is set by connecting a resistor between this pin and ground.
SD (Pin 12) - IC Logic Shutdown. When this pin is pulled low the chip turns off the high side switch and turns on the low side switch. While
this pin is low, the IC will not start up. An internal 20µA pull-up connects this pin to VCC.
HG (Pin 14) - Gate drive for the high-side N-channel MOSFET. This signal is interlocked with LG to avoid shoot-through problems.
These devices have limited built-in ESD protection. The leads should be shorted together or the device placed in conductive foam
during storage or handling to prevent electrostatic damage to the MOS gates.
2
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Absolute Maximum Ratings (1) (2)
VCC
7V
BOOTV
21V
Junction Temperature
150°C
Storage Temperature
−65°C to 150°C
Soldering Information
Lead Temperature (soldering, 10sec)
260°C
Infrared or Convection (20sec)
235°C
ESD Rating
(1)
(2)
(3)
(3)
2 kV
Absolute maximum ratings indicate limits beyond which damage to the device may occur. Operating ratings indicate conditions for
which the device operates correctly. Opearting Ratings do not imply ensured performance limits.
If Military/Aerospace specified devices are required, please contact the Texas Instruments Sales Office/ Distributors for availability and
specifications.
The human body model is a 100pF capacitor discharged through a 1.5k resistor into each pin.
Operating Ratings
Supply Voltage (VCC)
4.5V to 5.5V
−40°C to +125°C
Junction Temperature Range
Thermal Resistance (θJA)
155°C/W
Electrical Characteristics
VCC = 5V unless otherwise indicated. Typicals and limits appearing in plain type apply for TA=TJ=+25°C. Limits appearing in
boldface type apply over full Operating Temperature Range. Datasheet min/max specification limits are ensured by design,
test, or statistical analysis.
Symbol
VFB_ADJ
VON
Parameter
Conditions
FB Pin Voltage
UVLO Thresholds
Min
Typ
Max
VCC = 4.5V, 0°C to +125°C
0.591
0.6
0.609
VCC = 5V, 0°C to +125°C
0.591
0.6
0.609
VCC = 5.5V, 0°C to +125°C
0.591
0.6
0.609
VCC = 4.5V, −40°C to +125°C
0.589
0.6
0.609
VCC = 5V, −40°C to +125°C
0.589
0.6
0.609
VCC = 5.5V, −40°C to +125°C
0.589
0.6
0.609
Rising
Falling
4.2
3.6
Units
V
V
SD = 5V, FB = 0.55V
Fsw = 600kHz
1
1.5
2
SD = 5V, FB = 0.65V
Fsw = 600kHz
0.8
1.7
2.2
Shutdown VCC Current
SD = 0V
0.15
0.4
0.7
tPWGD1
PWGD Pin Response Time
FB Voltage Going Up
6
tPWGD2
PWGD Pin Response Time
FB Voltage Going Down
6
µs
20
µA
IQ-V5
ISD
ISS-ON
ISS-OC
ISEN-TH
Operating VCC Current
mA
SD Pin Internal Pull-up Current
SS Pin Source Current
SS Voltage = 2.5V
0°C to +125°C
-40°C to +125°C
SS Pin Sink Current During Over
Current
SS Voltage = 2.5V
ISEN Pin Source Current Trip Point
0°C to +125°C
-40°C to +125°C
8
5
11
11
µs
15
15
95
35
28
50
50
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µA
µA
65
65
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mA
µA
3
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Electrical Characteristics (continued)
VCC = 5V unless otherwise indicated. Typicals and limits appearing in plain type apply for TA=TJ=+25°C. Limits appearing in
boldface type apply over full Operating Temperature Range. Datasheet min/max specification limits are ensured by design,
test, or statistical analysis.
Symbol
Parameter
Conditions
Min
Typ
Max
Units
ERROR AMPLIFIER
GBW
G
Error Amplifier Unity Gain
Bandwidth
5
MHz
Error Amplifier DC Gain
60
dB
SR
Error Amplifier Slew Rate
6
V/µA
IFB
FB Pin Bias Current
FB = 0.55V
FB = 0.65V
IEAO
EAO Pin Current Sourcing and
Sinking
VEAO = 2.5, FB = 0.55V
VEAO = 2.5, FB = 0.65V
2.8
0.8
mA
VEA
Error Amplifier Maximum Swing
Minimum
Maximum
1.2
3.2
V
BOOT Pin Quiescent Current
BOOTV = 12V, EN = 0
0°C to +125°C
-40°C to +125°C
95
95
0
0
15
30
100
155
nA
GATE DRIVE
IQ-BOOT
160
215
µA
RDS1
Top FET Driver Pull-Up ON
resistance
BOOT-SW = 5V@350mA
3
Ω
RDS2
Top FET Driver Pull-Down ON
resistance
BOOT-SW = 5V@350mA
2
Ω
RDS3
Bottom FET Driver Pull-Up ON
resistance
BOOT-SW = 5V@350mA
3
Ω
RDS4
Bottom FET Driver Pull-Down ON
resistance
BOOT-SW = 5V@350mA
2
Ω
OSCILLATOR
fOSC
D
PWM Frequency
Max Duty Cycle
RFADJ = 590kΩ
50
RFADJ = 88.7kΩ
300
RFADJ = 42.2kΩ, 0°C to +125°C
500
600
700
RFADJ = 42.2kΩ, -40°C to +125°C
490
600
700
RFADJ = 17.4kΩ
1400
RFADJ = 11.3kΩ
2000
fPWM = 300kHz
fPWM = 600kHz
90
88
kHz
%
LOGIC INPUTS AND OUTPUTS
VSD-IH
SD Pin Logic High Trip Point
VSD-IL
SD Pin Logic Low Trip Point
0°C to +125°C
-40°C to +125°C
1.3
1.25
1.6
1.6
PWGD Pin Trip Points
FB Voltage Going Down
0°C to +125°C
-40°C to +125°C
0.413
0.410
0.430
0.430
0.446
0.446
V
FB Voltage Going Up
0°C to +125°C
-40°C to +125°C
0.691
0.688
0.710
0.710
0.734
0.734
V
VPWGD-TH-LO
VPWGD-TH-HI
VPWGD-HYS
4
2.6
PWGD Pin Trip Points
PWGD Hysteresis (LM2737 only)
FB Voltage Going Down FB Voltage
Going Up
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35
110
3.5
V
V
mV
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Typical Performance Characteristics
Efficiency (VO = 1.5V)
FSW = 300kHz, TA = 25°C
Efficiency (VO = 3.3V)
FSW = 300kHz, TA = 25°C
100
100
Vin = 5V
Vin = 3.3V
90
90
EFFICIENCY (%)
EFFICIENCY (%)
80
Vin = 5V
70
60
50
Vin = 12V
40
80
70
50
40
30
30
0.1
20
0.2
1
3
5
9
7
0.5
2
4
6
8
10
OUTPUT CURRENT (A)
OUTPUT CURRENT (A)
Figure 2.
Figure 3.
VCC Operating Current
vs
Temperature
FSW = 600kHz, No-Load
Bootpin Current
vs
Temperature for BOOTV = 12V
FSW = 600kHz, Si4826DY FET, No-Load
30.3
1.64
1.62
30.1
Without
Bootstrap
(Vboot = 12V)
1.6
BOOT PIN CURRENT (mA)
OPEARTING CURRENT(mA)
Vin = 12V
60
1.58
1.56
With
Bootstrap
(Vboot = 5V)
1.54
1.52
1.5
29.9
29.7
29.5
29.3
29.1
1.48
28.9
1.46
0
20
35
55
75
95
115
AMBIENT TEMPERATURE ( C)
Figure 4.
Figure 5.
Bootpin Current
vs
Temperature with 5V Bootstrap
FSW = 600kHz, Si4826DY FET, No-Load
PWM Frequency
vs
Temperature
for RFADJ = 43.2kΩ
8.6
630
8.4
628
8.2
626
PWM FREQUENCY (kHz)
BOOT PIN CURRENT (mA)
0 10 20 25 35 45 55 65 75 85 95105115 125
AMBIENT TEMPERATURE (oC)
o
8
7.8
7.6
7.4
7.2
624
622
620
618
616
614
7
0 10 20 25 35 45 55 65 75 85 95 105115125
612
o
AMBIENT TEMPERATURE ( C)
Figure 6.
0 10 20 25 35 45 55 65 75 85 95 105115 125
AMBIENT TEMPERATURE (oC)
Figure 7.
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Typical Performance Characteristics (continued)
RFADJ
vs
PWM Frequency
(in 100 to 800kHz range), TA = 25°C
RFADJ
vs
PWM Frequency
(in 900 to 2000kHz range), TA = 25°C
500
30
400
RF-ADJ (k:)
RF-ADJ (k:)
25
300
200
20
15
100
0
100 150 200 250 300 350 400450 500 600 700 800
10
9001000110012001300140015001600170018001900
PWM FREQUENCY (kHz)
PWM FREQUENCY (kHz)
Figure 8.
Figure 9.
VCC Operating Current Plus Boot Current vs
PWM Frequency (Si4826DY FET, TA = 25°C)
Switch Waveforms (HG Falling)
VIN = 5V, VO = 1.8V
IO = 3A, CSS = 10nF
FSW = 600kHz
40
VCC PLUS BOOT CURRENT
35
30
25
20
15
10
5
0
100 300 500 700 9001100 13001500 17001900
PWM FREQUENCY (kHz)
6
Figure 10.
Figure 11.
Switch Waveforms (HG Rising)
VIN = 5V, VO = 1.8V
IO = 3A, FSW = 600kHz
Start-Up (No-Load)
VIN = 10V, VO = 1.2V
CSS = 10nF, FSW = 300kHz
Figure 12.
Figure 13.
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Typical Performance Characteristics (continued)
Start-Up (Full-Load)
VIN = 10V, VO = 1.2V
IO = 10A, CSS = 10nF
FSW = 300kHz
Start Up (No-Load, 10x CSS)
VIN = 10V, VO = 1.2V
CSS = 100nF, FSW = 300kHz
Figure 14.
Figure 15.
Start Up (Full Load, 10x CSS)
VIN = 10V, VO = 1.2V
IO = 10A, CSS = 100nF
FSW = 300kHz
Shutdown
VIN = 10V, VO = 1.2V
IO = 10A, CSS = 10nF
FSW = 300kHz
Figure 16.
Figure 17.
Start Up (Full Load, 10x CSS)
VIN = 10V, VO = 1.2V
IO = 10A, CSS = 100nF
FSW = 300kHz
Load Transient Response (IO = 0 to 4A)
VIN = 12V, VO = 1.2V
FSW = 300kHz
Figure 18.
Figure 19.
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Typical Performance Characteristics (continued)
8
Load Transient Response (IO = 4 to 0A)
VIN = 12V, VO = 1.2V
FSW = 300kHz
Line Transient Response (VIN =5V to 12V)
VO = 1.2V, IO = 5A
FSW = 300kHz
Figure 20.
Figure 21.
Line Transient Response (VIN =12V to 5V)
VO = 1.2V, IO = 5A
FSW = 300kHz
Line Transient Response
VO = 1.2V, IO = 5A
FSW = 300kHz
Figure 22.
Figure 23.
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Block Diagram
SD
FREQ
Vcc
CLOCK &
RAMP
UVLO
PGND
PGND
SGND
20PA
off
LOGIC
BOOT
SHUT
DOWN
LATCH
10Ps
DELAY
HG
PWGD
3.05V
10PA
HIGH
LOW
LG
0.708V
tol.=+/-2%
0.42V
tol.=+/-2%
hyst.=12%
S
OUTPUT CLAMP
HI: 3.25V
LO: 1.25V
SS
3.25V
oc
95P$
R
1.25V
R>S
SS
CMP
off
off
SYNCHRONOUS
DRIVER LOGIC
PWM
50PA
BG =
0.6V
ISEN
ILIM
EA
oc
FB
EAO
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APPLICATION INFORMATION
THEORY OF OPERATION
The LM2727 is a voltage-mode, high-speed synchronous buck regulator with a PWM control scheme. It is
designed for use in set-top boxes, thin clients, DSL/Cable modems, and other applications that require high
efficiency buck converters. It has power good (PWRGD), output shutdown (SD), over voltage protection (OVP)
and under voltage protection (UVP). The over-voltage and under-voltage signals are OR gated to drive the
Power Good signal and a shutdown latch, which turns off the high side gate and turns on the low side gate if
pulled low. Current limit is achieved by sensing the voltage VDS across the low side FET. During current limit the
high side gate is turned off and the low side gate turned on. The soft start capacitor is discharged by a 95µA
source (reducing the maximum duty cycle) until the current is under control. The LM2737 does not latch off
during UVP or OVP, and uses the HIGH and LOW comparators for the powergood function only.
START UP
When VCC exceeds 4.2V and the enable pin EN sees a logic high the soft start capacitor begins charging through
an internal fixed 10µA source. During this time the output of the error amplifier is allowed to rise with the voltage
of the soft start capacitor. This capacitor, Css, determines soft start time, and can be determined approximately
by:
(1)
An application for a microprocessor might need a delay of 3ms, in which case CSS would be 12nF. For a different
device, a 100ms delay might be more appropriate, in which case CSS would be 400nF. (390 10%) During soft
start the PWRGD flag is forced low and is released when the voltage reaches a set value. At this point this chip
enters normal operation mode, the Power Good flag is released, and the OVP and UVP functions begin to
monitor Vo.
NORMAL OPERATION
While in normal operation mode, the LM2727/37 regulates the output voltage by controlling the duty cycle of the
high side and low side FETs. The equation governing output voltage is:
(2)
The PWM frequency is adjustable between 50kHz and 2MHz and is set by an external resistor, RFADJ, between
the FREQ pin and ground. The resistance needed for a desired frequency is approximately:
(3)
MOSFET GATE DRIVERS
The LM2727/37 has two gate drivers designed for driving N-channel MOSFETs in a synchronous mode. Power
for the drivers is supplied through the BOOTV pin. For the high side gate (HG) to fully turn on the top FET, the
BOOTV voltage must be at least one VGS(th) greater than Vin. (BOOTV ≥ 2*Vin) This voltage can be supplied by
a separate, higher voltage source, or supplied from a local charge pump structure. In a system such as a
desktop computer, both 5V and 12V are usually available. Hence if Vin was 5V, the 12V supply could be used for
BOOTV. 12V is more than 2*Vin, so the HG would operate correctly. For a BOOTV of 12V, the initial gate
charging current is 2A, and the initial gate discharging current is typically 6A.
10
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5V
Cb
BOOTV
+
HG
Vo
LM27x7
+
LG
Figure 24. BOOTV Supplied by Charge Pump
In a system without a separate, higher voltage, a charge pump (bootstrap) can be built using a diode and small
capacitor, Figure 24. The capacitor serves to maintain enough voltage between the top FET gate and source to
control the device even when the top FET is on and its source has risen up to the input voltage level.
The LM2727/37 gate drives use a BiCMOS design. Unlike some other bipolar control ICs, the gate drivers have
rail-to-rail swing, ensuring no spurious turn-on due to capacitive coupling.
POWER GOOD SIGNAL
The power good signal is the or-gated flag representing over-voltage and under-voltage protection. If the output
voltage is 18% over it's nominal value, VFB = 0.7V, or falls 30% below that value, VFB = 0.41V, the power good
flag goes low. The converter then turns off the high side gate, and turns on the low side gate. Unlike the output
(LM2727 only) the power good flag is not latched off. It will return to a logic high whenever the feedback pin
voltage is between 70% and 118% of 0.6V.
UVLO
The 4.2V turn-on threshold on VCC has a built in hysteresis of 0.6V. Therefore, if VCC drops below 3.6V, the chip
enters UVLO mode. UVLO consists of turning off the top FET, turning on the bottom FET, and remaining in that
condition until VCC rises above 4.2V. As with shutdown, the soft start capacitor is discharged through a FET,
ensuring that the next start-up will be smooth.
CURRENT LIMIT
Current limit is realized by sensing the voltage across the low side FET while it is on. The RDSON of the FET is a
known value, hence the current through the FET can be determined as:
VDS = I * RDSON
(4)
The current limit is determined by an external resistor, RCS, connected between the switch node and the ISEN
pin. A constant current of 50µA is forced through Rcs, causing a fixed voltage drop. This fixed voltage is
compared against VDS and if the latter is higher, the current limit of the chip has been reached. RCS can be found
by using the following:
RCS = RDSON(LOW) * ILIM/50µA
(5)
For example, a conservative 15A current limit in a 10A design with a minimum RDSON of 10mΩ would require a
3.3kΩ resistor. Because current sensing is done across the low side FET, no minimum high side on-time is
necessary. In the current limit mode the LM2727/37 will turn the high side off and the keep low side on for as
long as necessary. The chip also discharges the soft start capacitor through a fixed 95µA source. In this way,
smooth ramping up of the output voltage as with a normal soft start is ensured. The output of the LM2727/37
internal error amplifier is limited by the voltage on the soft start capacitor. Hence, discharging the soft start
capacitor reduces the maximum duty cycle D of the controller. During severe current limit, this reduction in duty
cycle will reduce the output voltage, if the current limit conditions lasts for an extended time.
During the first few nanoseconds after the low side gate turns on, the low side FET body diode conducts. This
causes an additional 0.7V drop in VDS. The range of VDS is normally much lower. For example, if RDSON were
10mΩ and the current through the FET was 10A, VDS would be 0.1V. The current limit would see 0.7V as a 70A
current and enter current limit immediately. Hence current limit is masked during the time it takes for the high
side switch to turn off and the low side switch to turn on.
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UVP/OVP
The output undervoltage protection and overvoltage protection mechanisms engage at 70% and 118% of the
target output voltage, respectively. In either case, the LM2727 will turn off the high side switch and turn on the
low side switch, and discharge the soft start capacitor through a MOSFET switch. The chip remains in this state
until the shutdown pin has been pulled to a logic low and then released. The UVP function is masked only during
the first charging of the soft start capacitor, when voltage is first applied to the VCC pin. In contrast, the LM2737 is
designed to continue operating during UVP or OVP conditions, and to resume normal operation once the fault
condition is cleared. As with the LM2727, the powergood flag goes low during this time, giving a logic-level
warning signal.
SHUT DOWN
If the shutdown pin SD is pulled low, the LM2727/37 discharges the soft start capacitor through a MOSFET
switch. The high side switch is turned off and the low side switch is turned on. The LM2727/37 remains in this
state until SD is released.
DESIGN CONSIDERATIONS
The following is a design procedure for all the components needed to create the circuit shown in Figure 26 in the
Example Circuits section, a 5V in to 1.2V out converter, capable of delivering 10A with an efficiency of 85%. The
switching frequency is 300kHz. The same procedures can be followed to create the circuit shown in Figure 26,
Figure 27, and to create many other designs with varying input voltages, output voltages, and output currents.
INPUT CAPACITOR
The input capacitors in a Buck switching converter are subjected to high stress due to the input current
waveform, which is a square wave. Hence input caps are selected for their ripple current capability and their
ability to withstand the heat generated as that ripple current runs through their ESR. Input rms ripple current is
approximately:
(6)
The power dissipated by each input capacitor is:
(7)
Here, n is the number of capacitors, and indicates that power loss in each cap decreases rapidly as the number
of input caps increase. The worst-case ripple for a Buck converter occurs during full load, when the duty cycle D
= 50%.
In the 5V to 1.2V case, D = 1.2/5 = 0.24. With a 10A maximum load the ripple current is 4.3A. The Sanyo
10MV5600AX aluminum electrolytic capacitor has a ripple current rating of 2.35A, up to 105°C. Two such
capacitors make a conservative design that allows for unequal current sharing between individual caps. Each
capacitor has a maximum ESR of 18mΩ at 100 kHz. Power loss in each device is then 0.05W, and total loss is
0.1W. Other possibilities for input and output capacitors include MLCC, tantalum, OSCON, SP, and POSCAPS.
INPUT INDUCTOR
The input inductor serves two basic purposes. First, in high power applications, the input inductor helps insulate
the input power supply from switching noise. This is especially important if other switching converters draw
current from the same supply. Noise at high frequency, such as that developed by the LM2727 at 1MHz
operation, could pass through the input stage of a slower converter, contaminating and possibly interfering with
its operation.
An input inductor also helps shield the LM2727 from high frequency noise generated by other switching
converters. The second purpose of the input inductor is to limit the input current slew rate. During a change from
no-load to full-load, the input inductor sees the highest voltage change across it, equal to the full load current
times the input capacitor ESR. This value divided by the maximum allowable input current slew rate gives the
minimum input inductance:
12
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(8)
In the case of a desktop computer system, the input current slew rate is the system power supply or "silver box"
output current slew rate, which is typically about 0.1A/µs. Total input capacitor ESR is 9mΩ, hence ΔV is
10*0.009 = 90 mV, and the minimum inductance required is 0.9µH. The input inductor should be rated to handle
the DC input current, which is approximated by:
(9)
In this case IIN-DC is about 2.8A. One possible choice is the TDK SLF12575T-1R2N8R2, a 1.2µH device that can
handle 8.2Arms, and has a DCR of 7mΩ.
OUTPUT INDUCTOR
The output inductor forms the first half of the power stage in a Buck converter. It is responsible for smoothing the
square wave created by the switching action and for controlling the output current ripple. (ΔIo) The inductance is
chosen by selecting between tradeoffs in efficiency and response time. The smaller the output inductor, the more
quickly the converter can respond to transients in the load current. As shown in the efficiency calculations,
however, a smaller inductor requires a higher switching frequency to maintain the same level of output current
ripple. An increase in frequency can mean increasing loss in the FETs due to the charging and discharging of the
gates. Generally the switching frequency is chosen so that conduction loss outweighs switching loss. The
equation for output inductor selection is:
(10)
Plugging in the values for output current ripple, input voltage, output voltage, switching frequency, and assuming
a 40% peak-to-peak output current ripple yields an inductance of 1.5µH. The output inductor must be rated to
handle the peak current (also equal to the peak switch current), which is (Io + 0.5*ΔIo). This is 12A for a 10A
design. The Coilcraft D05022-152HC is 1.5µH, is rated to 15Arms, and has a DCR of 4mΩ.
OUTPUT CAPACITOR
The output capacitor forms the second half of the power stage of a Buck switching converter. It is used to control
the output voltage ripple (ΔVo) and to supply load current during fast load transients.
In this example the output current is 10A and the expected type of capacitor is an aluminum electrolytic, as with
the input capacitors. (Other possibilities include ceramic, tantalum, and solid electrolyte capacitors, however the
ceramic type often do not have the large capacitance needed to supply current for load transients, and tantalums
tend to be more expensive than aluminum electrolytic.) Aluminum capacitors tend to have very high capacitance
and fairly low ESR, meaning that the ESR zero, which affects system stability, will be much lower than the
switching frequency. The large capacitance means that at switching frequency, the ESR is dominant, hence the
type and number of output capacitors is selected on the basis of ESR. One simple formula to find the maximum
ESR based on the desired output voltage ripple, ΔVo and the designed output current ripple, ΔIo, is:
(11)
In this example, in order to maintain a 2% peak-to-peak output voltage ripple and a 40% peak-to-peak inductor
current ripple, the required maximum ESR is 6mΩ. Three Sanyo 10MV5600AX capacitors in parallel will give an
equivalent ESR of 6mΩ. The total bulk capacitance of 16.8mF is enough to supply even severe load transients.
Using the same capacitors for both input and output also keeps the bill of materials simple.
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MOSFETS
MOSFETS are a critical part of any switching controller and have a direct impact on the system efficiency. In this
case the target efficiency is 85% and this is the variable that will determine which devices are acceptable. Loss
from the capacitors, inductors, and the LM2727 itself are detailed in the Efficiency section, and come to about
0.54W. To meet the target efficiency, this leaves 1.45W for the FET conduction loss, gate charging loss, and
switching loss. Switching loss is particularly difficult to estimate because it depends on many factors. When the
load current is more than about 1 or 2 amps, conduction losses outweigh the switching and gate charging losses.
This allows FET selection based on the RDSON of the FET. Adding the FET switching and gate-charging losses to
the equation leaves 1.2W for conduction losses. The equation for conduction loss is:
PCnd = D(I2o * RDSON *k) + (1-D)(I2o * RDSON *k)
(12)
The factor k is a constant which is added to account for the increasing RDSON of a FET due to heating. Here, k =
1.3. The Si4442DY has a typical RDSON of 4.1mΩ. When plugged into the equation for PCND the result is a loss of
0.533W. If this design were for a 5V to 2.5V circuit, an equal number of FETs on the high and low sides would be
the best solution. With the duty cycle D = 0.24, it becomes apparent that the low side FET carries the load
current 76% of the time. Adding a second FET in parallel to the bottom FET could improve the efficiency by
lowering the effective RDSON. The lower the duty cycle, the more effective a second or even third FET can be. For
a minimal increase in gate charging loss (0.054W) the decrease in conduction loss is 0.15W. What was an 85%
design improves to 86% for the added cost of one SO-8 MOSFET.
CONTROL LOOP COMPONENTS
The circuit is this design example and the others shown in the Example Circuits section have been compensated
to improve their DC gain and bandwidth. The result of this compensation is better line and load transient
responses. For the LM2727, the top feedback divider resistor, Rfb2, is also a part of the compensation. For the
10A, 5V to 1.2V design, the values are:
Cc1 = 4.7pF 10%, Cc2 = 1nF 10%, Rc = 229kΩ 1%. These values give a phase margin of 63° and a bandwidth
of 29.3kHz.
SUPPORT CAPACITORS AND RESISTORS
The Cinx capacitors are high frequency bypass devices, designed to filter harmonics of the switching frequency
and input noise. Two 1µF ceramic capacitors with a sufficient voltage rating (10V for the Circuit of Figure 26) will
work well in almost any case.
Rbypass and Cbypass are standard filter components designed to ensure smooth DC voltage for the chip supply
and for the bootstrap structure, if it is used. Use 10Ω for the resistor and a 2.2µF ceramic for the cap. Cb is the
bootstrap capacitor, and should be 0.1µF. (In the case of a separate, higher supply to the BOOTV pin, this 0.1µF
cap can be used to bypass the supply.) Using a Schottky device for the bootstrap diode allows the minimum drop
for both high and low side drivers. The On Semiconductor BAT54 or MBR0520 work well.
Rp is a standard pull-up resistor for the open-drain power good signal, and should be 10kΩ. If this feature is not
necessary, it can be omitted.
RCS is the resistor used to set the current limit. Since the design calls for a peak current magnitude (Io + 0.5 *
ΔIo) of 12A, a safe setting would be 15A. (This is well below the saturation current of the output inductor, which is
25A.) Following the equation from the Current Limit section, use a 3.3kΩ resistor.
RFADJ is used to set the switching frequency of the chip. Following the equation in the Theory of Operation
section, the closest 1% tolerance resistor to obtain fSW = 300kHz is 88.7kΩ.
CSS depends on the users requirements. Based on the equation for CSS in the Theory of Operation section, for a
3ms delay, a 12nF capacitor will suffice.
14
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EFFICIENCY CALCULATIONS
A reasonable estimation of the efficiency of a switching controller can be obtained by adding together the loss is
each current carrying element and using the equation:
(13)
The following shows an efficiency calculation to complement the Circuit of Figure 26. Output power for this circuit
is 1.2V x 10A = 12W.
Chip Operating Loss
PIQ = IQ-VCC *VCC
(14)
2mA x 5V = 0.01W
FET Gate Charging Loss
PGC = n * VCC * QGS * fOSC
(15)
The value n is the total number of FETs used. The Si4442DY has a typical total gate charge, QGS, of 36nC and
an rds-on of 4.1mΩ. For a single FET on top and bottom: 2*5*36E-9*300,000 = 0.108W
FET Switching Loss
PSW = 0.5 * Vin * IO * (tr + tf)* fOSC
(16)
-9
The Si4442DY has a typical rise time tr and fall time tf of 11 and 47ns, respectively. 0.5*5*10*58E *300,000 =
0.435W
FET Conduction Loss
PCn = 0.533W
(17)
Input Capacitor Loss
(18)
(19)
2
4.28 *0.018/2 = 0.084W
Input Inductor Loss
PLin = I2in * DCRinput-L
(20)
(21)
2
2.82 *0.007 = 0.055W
Output Inductor Loss
PLout = I2o * DCRoutput-L
(22)
2
10 *0.004 = 0.4W
System Efficiency
(23)
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Example Circuits
+5V
D1
Rin
10
Cin
2.2u
Rfadj
0.1u
Q1
BOOT
SD
Css
12n
2.7 uH
14.4 A, 4.5 m:
Rcs
ISEN
PWGD
LM27x7
LG
SS
PGND
SGND
PGND
Lin
+ Cin1,2
2 x 10 uF
25V, 3.3A
Cinx
1uF
25V
HG
Vcc
FREQ
88.7k
1.2 uH
8.2 A, 6.9 m:
Cboot
Vin = 12V
Vo = 3.3V@10A
L1
1.8k
Q2
+ Co1-4
4 x 100 uF
10V, 55 m:
Rfb2
49.9k
Rc2
Cc3
FB
EAO
8.45k
470p
Rfb1
11k
Cc1
Cc2
6.8p
Rc1
143.3k
270p
Figure 25. 5V-16V to 3.3V, 10A, 300kHz
This circuit and the one featured on the front page have been designed to deliver high current and high efficiency
in a small package, both in area and in height The tallest component in this circuit is the inductor L1, which is
6mm tall. The compensation has been designed to tolerate input voltages from 5 to 16V.
D1
1.2 uH
8.2 A, 6.9 m:
Cboot
Rin
10
0.1u
Cinx1, 2
2x1uF
10V
Q1
Cin
2.2u
Rfadj
Vcc
HG
SD
BOOT
PWGD
Css
12n
1.5 uH
15 A, 4 m:
ISEN
LM27x7
FREQ
88.7k
Rcs
SS
LG
1.5k
SGND
Vin = 5V
Lin
Cin1,2
2 x 5600uF
10V, 2.35A
Vo = 1.2V@10A
L1
Q2
PGND
PGND
EAO
+
Rfb2
4.99k
+ Co1-3
3 x 5600 uF
10V, 3.1A
18 m:
FB
Rfb1
4.99k
Cc1
Cc2
270p
4.7p
Rc1
229k
Figure 26. 5V to 1.2V, 10A, 300kHz
This circuit design, detailed in the Design Considerations section, uses inexpensive aluminum capacitors and offthe-shelf inductors. It can deliver 10A at better than 85% efficiency. Large bulk capacitance on input and output
ensure stable operation.
16
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+12V
Vin = 5V
Cc
0.1u
Rin
10
Cin
2.2u
Vcc
SD
BOOT
PWGD
Rfadj
Css
12n
LG
SS
PGND
SGND
PGND
EAO
Cin1
100 uF
10V, 1.9A
2.2 uH
6.1A, 12 m:
Rcs
ISEN
LM27x7
FREQ
43.2k
+
Q1/Q2
HG
Vo = 1.8V@3A
L1
2.7k
+
Rfb2
4.99k
Co1
1 x 220 uF
4V, 55 m:
FB
Rfb1
2.49k
Cc1
Cc2
10p
560p
Rc1
51.1k
Figure 27. 5V to 1.8V, 3A, 600kHz
The example circuit of Figure 27 has been designed for minimum component count and overall solution size. A
switching frequency of 600kHz allows the use of small input/output capacitors and a small inductor. The
availability of separate 5V and 12V supplies (such as those available from desk-top computer supplies) and the
low current further reduce component count. Using the 12V supply to power the MOSFET drivers eliminates the
bootstrap diode, D1. At low currents, smaller FETs or dual FETs are often the most efficient solutions. Here, the
Si4826DY, an asymmetric dual FET in an SO-8 package, yields 92% efficiency at a load of 2A.
1 uH
4.5 A, 7.5 m:
+5V
D1
Cboot
Rin
10
Cin
2.2u
Rfadj
Vcc
Css
12n
Q1
HG
BOOT
SD
PWGD
Rcs
1 uH
11 A, 3.7 m:
3.3k
L1
ISEN
FREQ
49.9k
Vin = 3.3V
Lin
0.1u
LG
LM27x7
Q2
SS
PGND
SGND
PGND
EAO
Cinx
1uF
10V
+ Cin1
1 x 5600 uF
10V, 2.35A
Vo = 0.8V@5A
Rfb2
4.99k
+ Co1,2
2 x 4700 uF
16V, 2.8A
FB
Rfb1
14.9k
Cc1
Cc2
680p
4.7p
Rc1
147k
Figure 28. 3.3V to 0.8V, 5A, 500kHz
The circuit of Figure 28 demonstrates the LM2727 delivering a low output voltage at high efficiency (87%) A
separate 5V supply is required to run the chip, however the input voltage can be as low as 2.2
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+5V
D1
1uH
6.4A, 7.3 m:
Cboot
Rin
10
Vin = 5 to 15V
Lin
0.1u
+
Vcc
Cin
2.2u
SD
BOOT
PWGD
Rfadj
Rcs
ISEN
LM27x7
FREQ
17.4k
LG
SS
PGND
SGND
PGND
EAO
+
Rfb2
10k
Rc2
66.5
22p
Co1
1 x 15uF
25V 3.1mohm
Cc3
680p
Rfb1
4.99k
Cc1
Cc2
Vo = 1.8V@1A
L1
1.5k
FB
Css
1 x 15uF
25V, 3.3A
Q1/Q2
3.3uH
4.1A, 17.4 m:
HG
Rc1
39n
680p
10.7k
1uH
6.4 A, 7.3 m:
Vin = 5 to 15V
Lin
+5V
D1
Cboot
Rin
10
0.1u
Vcc
Cin
2.2u
HG
SD
BOOT
PWGD
Rfadj
FREQ
17.4k
Rcs
ISEN
LM27x7
LG
SS
PGND
SGND
PGND
Vo = 3.3V@1A
L1
1.5k
Rfb2
10k
Rc2
EAO
+ Cin1
1 x 15uF
25V, 3.3A
Q1/Q2
4.7uH
3.4A, 26 m:
+ Co1
1 x 15uF
25V 3.1 m:
Cc3
FB
54.9
820p
Cc1
Cc2
1n
27p
Rfb1
2.21k
Rc1
12.1k
Figure 29. 1.8V and 3.3V, 1A, 1.4MHz, Simultaneous
The circuits in Figure 29 are intended for ADSL applications, where the high switching frequency keeps noise out
of the data transmission range. In this design, the 1.8 and 3.3V outputs come up simultaneously by using the
same softstart capacitor. Because two current sources now charge the same capacitor, the capacitance must be
doubled to achieve the same softstart time. (Here, 40nF is used to achieve a 5ms softstart time.) A common
softstart capacitor means that, should one circuit enter current limit, the other circuit will also enter current limit.
In addition, if both circuits are built with the LM2727, a UVP or OVP fault on one circuit will cause both circuits to
latch off. The additional compensation components Rc2 and Cc3 are needed for the low ESR, all ceramic output
capacitors, and the wide (3x) range of Vin.
18
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To 2nd LM27x7
Vin = 11 to 13V
+5V
LM78L05
D1
1uH, 6.4A
7.3 m:
Cboot
0.1u
Cin
2.2u
BOOT
SD
LM27x7
FREQ
32.5k
Css
12n
Rcs
+
Cinx
10uF
16V
Cin1
680uF
16V, 1.54A
Vo = 3.3V@3A
ISEN
PWGD
Rfadj
Q1/Q2
4.2uH, 5.5A
15 m:
HG
Vcc
2k
LG
SS
PGND
SGND
PGND
+
Rfb2
10k
2.37k
4.7n
Rfb1
2.21k
Cc1
Cc2
Cox
10uF
25V
Co1,2
2 x 680uF
16V 1.54A
Cc3
Rc2
FB
EAO
Vin = 11 to 13V
Lin
Rc1
8.2p
52.3k
1n
Figure 30. 12V Unregulated to 3.3V, 3A, 750kHz
This circuit shows the LM27x7 paired with a cost effective solution to provide the 5V chip power supply, using no
extra components other than the LM78L05 regulator itself. The input voltage comes from a 'brick' power supply
which does not regulate the 12V line tightly. Additional, inexpensive 10uF ceramic capacitors (Cinx and Cox)
help isolate devices with sensitive databands, such as DSL and cable modems, from switching noise and
harmonics.
+5V (low current source)
Cboot
D1
Vin = 12V
0.1u
Cin
2.2u
Rfadj
Vcc
HG
SD
BOOT
PWGD
FREQ
267k
Css
12n
ISEN
LM27x7
SS
SGND
+ Cin1
680uF
16V
1.54A
Vo = [email protected]
L1
LG
D2
PGND
Rfb2
10k
PGND
Rc2
EAO
Cinx
10uF
16V
Q1
47uH 2.7A
53 m:
Cc3
+ Co1,2
2 x 680uF
16V
26 m:
Cox
10uF
6.3V
FB
750
22n
Cc1
Cc2
3.9n
56p
Rfb1
1.37k
Rc1
61.9k
Figure 31. 12V to 5V, 1.8A, 100kHz
In situations where low cost is very important, the LM27x7 can also be used as an asynchronous controller, as
shown in the above circuit. Although a a schottky diode in place of the bottom FET will not be as efficient, it will
cost much less than the FET. The 5V at low current needed to run the LM27x7 could come from a zener diode or
inexpensive regulator, such as the one shown in Figure 30. Because the LM27x7 senses current in the low side
MOSFET, the current limit feature will not function in an asynchronous design. The ISEN pin should be left open
in this case.
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Table 1. Bill of Materials for Typical Application Circuit
ID
U1
Part Number
Type
Synchronous
Controller
LM2727
Q1, Q2
Si4884DY
L1
RLF7030T-1R5N6R1
N-MOSFET
Cin1, Cin2
C2012X5R1J106M
MLCC
Capacitor
Cinx
C3216X7R1E105K
Co1, Co2
6MV2200WG
Cboot
VJ1206X104XXA
Inductor
Size
Parameters
Qty.
Vendor
TSSOP-14
TSSOP-14
1
Texas
Instruments
SO-8
30V, 4.1mΩ, 36nC
1
Vishay
7.1x7.1x3.2mm
1.5µH, 6.1A 9.6mΩ
1
TDK
0805
10µF 6.3V
2
TDK
1206
1µF, 25V
1
TDK
10mm D 20mm H
2200µF 6.3V125mΩ
2
Sanyo
Capacitor
1206
0.1µF, 25V
1
Vishay
AL-E
Cin
C3216X7R1E225K
Capacitor
1206
0.1µF, 25V
1
TDK
Css
VJ1206X123KXX
Capacitor
1206
12nF, 25V
1
Vishay
Cc1
VJ1206A2R2KXX
Capacitor
1206
2.2pF 10%
1
Vishay
Cc2
VJ1206A181KXX
Capacitor
1206
180pF 10%
1
Vishay
Rin
CRCW1206100J
Resistor
1206
10Ω 5%
1
Vishay
Rfadj
CRCW12066342F
Resistor
1206
63.4kΩ 1%
1
Vishay
Rc1
CRCW12063923F
Resistor
1206
392kΩ 1%
1
Vishay
Rfb1
CRCW12061002F
Resistor
1206
10kΩ 1%
1
Vishay
Rfb2
CRCW12061002F
Resistor
1206
10kΩ 1%
1
Vishay
Rcs
CRCW1206222J
Resistor
1206
2.2kΩ 5%
1
Vishay
Table 2. Bill of Materials for Circuit of Figure 25
(Identical to BOM for 1.5V except as noted below)
ID
Part Number
Size
Parameters
Qty.
Vendor
L1
RLF12560T-2R7N110
Inductor
Type
12.5x12.8x6mm
2.7µH, 14.4A 4.5mΩ
1
TDK
Co1, Co2,
Co3, Co4
10TPB100M
POSCAP
7.3x4.3x2.8mm
100µF 10V 1.9Arms
4
Sanyo
Cc1
VJ1206A6R8KXX
Capacitor
1206
6.8pF 10%
1
Vishay
Cc2
VJ1206A271KXX
Capacitor
1206
270pF 10%
1
Vishay
Cc3
VJ1206A471KXX
Capacitor
1206
470pF 10%
1
Vishay
Rc2
CRCW12068451F
Resistor
1206
8.45kΩ 1%
1
Vishay
Rfb1
CRCW12061102F
Resistor
1206
11kΩ 1%
1
Vishay
Qty.
Vendor
1
Texas
Instruments
Table 3. Bill of Materials for Circuit of Figure 26
ID
20
Part Number
Type
Synchronous
Controller
Size
Parameters
U1
LM2727
Q1
Si4442DY
N-MOSFET
SO-8
30V, 4.1mΩ, @ 4.5V, 36nC
1
Vishay
Q2
Si4442DY
N-MOSFET
SO-8
30V, 4.1mΩ, @ 4.5V, 36nC
1
Vishay
D1
BAT-54
SOT-23
30V
1
Vishay
Lin
SLF12575T-1R2N8R2
Inductor
12.5x12.5x7.5mm
12µH, 8.2A, 6.9mΩ
1
Coilcraft
L1
D05022-152HC
Inductor
22.35x16.26x8mm
1.5µH, 15A,4mΩ
1
Coilcraft
16mm D 25mm H
5600µF10V 2.35Arms
2
Sanyo
Schottky Diode
Cin1, Cin2
10MV5600AX
Aluminum
Electrolytic
Cinx
TSSOP-14
C3216X7R1E105K
Capacitor
1206
1µF, 25V
1
TDK
Co1, Co2,
Co3
10MV5600AX
Aluminum
Electrolytic
16mm D 25mm H
5600µF10V 2.35Arms
2
Sanyo
Cboot
VJ1206X104XXA
Capacitor
1206
0.1µF, 25V
1
Vishay
Cin
C3216X7R1E225K
Capacitor
1206
2.2µF, 25V
1
TDK
Css
VJ1206X123KXX
Capacitor
1206
12nF, 25V
1
Vishay
Cc1
VJ1206A4R7KXX
Capacitor
1206
4.7pF 10%
1
Vishay
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Table 3. Bill of Materials for Circuit of Figure 26 (continued)
ID
Part Number
Size
Parameters
Qty.
Vendor
Cc2
VJ1206A102KXX
Capacitor
Type
1206
1nF 10%
1
Vishay
Rin
CRCW1206100J
Resistor
1206
10Ω 5%
1
Vishay
Rfadj
CRCW12068872F
Resistor
1206
88.7kΩ 1%
1
Vishay
Rc1
CRCW12062293F
Resistor
1206
229kΩ 1%
1
Vishay
Rfb1
CRCW12064991F
Resistor
1206
4.99kΩ 1%
1
Vishay
Rfb2
CRCW12064991F
Resistor
1206
4.99kΩ 1%
1
Vishay
Rcs
CRCW1206152J
Resistor
1206
1.5kΩ 5%
1
Vishay
Qty.
Vendor
1
Texas
Instruments
30V, 24mΩ/ 8nC
Top 16.5mΩ/ 15nC
1
Vishay
Table 4. Bill of Materials for Circuit of Figure 27
ID
Part Number
U1
LM2727
Type
Q1/Q2
Si4826DY
L1
DO3316P-222
Inductor
12.95x9.4x 5.21mm
2.2µH, 6.1A, 12mΩ
1
Coilcraft
Cin1
10TPB100ML
POSCAP
7.3x4.3x3.1mm
100µF 10V 1.9Arms
1
Sanyo
Co1
4TPB220ML
POSCAP
7.3x4.3x3.1mm
220µF 4V 1.9Arms
1
Sanyo
Cc
C3216X7R1E105K
Capacitor
1206
1µF, 25V
1
TDK
Cin
C3216X7R1E225K
Capacitor
1206
2.2µF, 25V
1
TDK
Css
VJ1206X123KXX
Capacitor
1206
12nF, 25V
1
Vishay
Cc1
VJ1206A100KXX
Capacitor
1206
10pF 10%
1
Vishay
Cc2
VJ1206A561KXX
Capacitor
1206
560pF 10%
1
Vishay
Rin
CRCW1206100J
Resistor
1206
10Ω 5%
1
Vishay
Rfadj
CRCW12064222F
Resistor
1206
42.2kΩ 1%
1
Vishay
Rc1
CRCW12065112F
Resistor
1206
51.1kΩ 1%
1
Vishay
Rfb1
CRCW12062491F
Resistor
1206
2.49kΩ 1%
1
Vishay
Rfb2
CRCW12064991F
Resistor
1206
4.99kΩ 1%
1
Vishay
Rcs
CRCW1206272J
Resistor
1206
2.7kΩ 5%
1
Vishay
Qty.
Vendor
1
Texas
Instruments
Synchronous
Controller
Asymetric Dual
N-MOSFET
Size
Parameters
TSSOP-14
SO-8
Table 5. Bill of Materials for Circuit of Figure 28
ID
Part Number
U1
LM2727
Type
Q1
Si4884DY
N-MOSFET
SO-8
30V, 13.5mΩ, @ 4.5V
15.3nC
1
Vishay
Q2
Si4884DY
N-MOSFET
SO-8
30V, 13.5mΩ, @ 4.5V
15.3nC
1
Vishay
SOT-23
30V
1
Vishay
7.29x7.29 3.51mm
1µH, 11A 3.7mΩ
1
Pulse
12x12x4.5 mm
1µH, 11A, 3.7mΩ
1
Pulse
16mm D 25mm H
5600µF 10V 2.35Arms
1
Sanyo
Synchronous
Controller
D1
BAT-54
Lin
P1166.102T
Schottky Diode
Inductor
Inductor
L1
P1168.102T
Cin1
10MV5600AX
Aluminum
Electrolytic
Size
Parameters
TSSOP-14
Cinx
C3216X7R1E105K
Capacitor
1206
1µF, 25V
1
TDK
Co1, Co2,
Co3
16MV4700WX
Aluminum
Electrolytic
12.5mm D 30mm H
4700µF 16V 2.8Arms
2
Sanyo
Cboot
VJ1206X104XXA
Capacitor
1206
0.1µF, 25V
1
Vishay
Cin
C3216X7R1E225K
Capacitor
1206
2.2µF, 25V
1
TDK
Css
VJ1206X123KXX
Capacitor
1206
12nF, 25V
1
Vishay
Cc1
VJ1206A4R7KXX
Capacitor
1206
4.7pF 10%
1
Vishay
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Table 5. Bill of Materials for Circuit of Figure 28 (continued)
ID
Part Number
Size
Parameters
Qty.
Vendor
Cc2
VJ1206A681KXX
Capacitor
Type
1206
680pF 10%
1
Vishay
Rin
CRCW1206100J
Resistor
1206
10Ω 5%
1
Vishay
Rfadj
CRCW12064992F
Resistor
1206
49.9kΩ 1%
1
Vishay
Rc1
CRCW12061473F
Resistor
1206
147kΩ 1%
1
Vishay
Rfb1
CRCW12061492F
Resistor
1206
14.9kΩ 1%
1
Vishay
Rfb2
CRCW12064991F
Resistor
1206
4.99kΩ 1%
1
Vishay
Rcs
CRCW1206332J
Resistor
1206
3.3kΩ 5%
1
Vishay
Qty.
Vendor
1
Texas
Instruments
30V, 24mΩ/ 8nC
Top 16.5mΩ/ 15nC
1
Vishay
Table 6. Bill of Materials for Circuit of Figure 29
ID
Part Number
U1
LM2727
Type
Q1/Q2
Si4826DY
Assymetric Dual
N-MOSFET
Schottky Diode
Synchronous
Controller
Size
Parameters
TSSOP-14
SO-8
D1
BAT-54
SOT-23
30V
1
Vishay
Lin
RLF7030T-1R0N64
Inductor
6.8x7.1x3.2mm
1µH, 6.4A, 7.3mΩ
1
TDK
Inductor
L1
RLF7030T-3R3M4R1
6.8x7.1x3.2mm
3.3µH, 4.1A, 17.4mΩ
1
TDK
Cin1
C4532X5R1E156M
MLCC
1812
15µF 25V 3.3Arms
1
Sanyo
Co1
C4532X5R1E156M
MLCC
1812
15µF 25V 3.3Arms
1
Sanyo
Cboot
VJ1206X104XXA
Capacitor
1206
0.1µF, 25V
1
TDK
Cin
C3216X7R1E225K
Capacitor
1206
2.2µF, 25V
1
TDK
Css
VJ1206X393KXX
Capacitor
1206
39nF, 25V
1
Vishay
Cc1
VJ1206A220KXX
Capacitor
1206
22pF 10%
1
Vishay
Cc2
VJ1206A681KXX
Capacitor
1206
680pF 10%
1
Vishay
Cc3
VJ1206A681KXX
Capacitor
1206
680pF 10%
1
Vishay
Rin
CRCW1206100J
Resistor
1206
10Ω 5%
1
Vishay
Rfadj
CRCW12061742F
Resistor
1206
17.4kΩ 1%
1
Vishay
Rc1
CRCW12061072F
Resistor
1206
10.7kΩ 1%
1
Vishay
Rc2
CRCW120666R5F
Resistor
1206
66.5Ω 1%
1
Vishay
Rfb1
CRCW12064991F
Resistor
1206
4.99kΩ 1%
1
Vishay
Rfb2
CRCW12061002F
Resistor
1206
10kΩ 1%
1
Vishay
Rcs
CRCW1206152J
Resistor
1206
1.5kΩ 5%
1
Vishay
Vendor
Table 7. Bill of Materials for 3.3V Circuit of Figure 29
(Identical to BOM for 1.8V except as noted below)
22
ID
Part Number
L1
RLF7030T-4R7M3R4
Cc1
VJ1206A270KXX
Cc2
Cc3
Rc1
Type
Size
Parameters
Qty.
6.8x7.1x 3.2mm
4.7µH, 3.4A, 26mΩ
1
TDK
Capacitor
1206
27pF 10%
1
Vishay
VJ1206X102KXX
Capacitor
1206
1nF 10%
1
Vishay
VJ1206A821KXX
Capacitor
1206
820pF 10%
1
Vishay
CRCW12061212F
Resistor
1206
12.1kΩ 1%
1
Vishay
Inductor
Rc2
CRCW12054R9F
Resistor
1206
54.9Ω 1%
1
Vishay
Rfb1
CRCW12062211F
Resistor
1206
2.21kΩ 1%
1
Vishay
Rfb2
CRCW12061002F
Resistor
1206
10kΩ 1%
1
Vishay
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SNVS205D – AUGUST 2002 – REVISED MARCH 2013
Table 8. Bill of Materials for Circuit of Figure 30
ID
Part Number
U1
LM2727
Synchronous Controller
Type
Qty.
Vendor
TSSOP-14
Size
U2
LM78L05
Q1/Q2
Si4826DY
D1
BAT-54
1
Texas
Instrument
s
Voltage Regulator
SO-8
1
Texas
Instrument
s
Assymetric Dual N-MOSFET
SO-8
30V, 24mΩ/ 8nC
Top 16.5mΩ/ 15nC
1
Vishay
SOT-23
30V
1
Vishay
TDK
Schottky Diode
Parameters
Lin
RLF7030T-1R0N64
Inductor
6.8x7.1x3.2mm
1µH, 6.4A, 7.3mΩ
1
L1
SLF12565T-4R2N5R5
Inductor
12.5x12.5x6.5mm
4.2µH, 5.5A, 15mΩ
1
TDK
Cin1
16MV680WG
D: 10mm L: 12.5mm
680µF 16V 3.4Arms
1
Sanyo
Al-E
Cinx
C3216X5R1C106M
MLCC
1210
10µF 16V 3.4Arms
1
TDK
Co1 Co2
16MV680WG
MLCC
1812
15µF 25V 3.3Arms
1
Sanyo
Vishay
Cox
C3216X5R10J06M
MLCC
1206
10µF 6.3V 2.7A
Cboot
VJ1206X104XXA
Capacitor
1206
0.1µF, 25V
1
TDK
Cin
C3216X7R1E225K
Capacitor
1206
2.2µF, 25V
1
TDK
Css
VJ1206X123KXX
Capacitor
1206
12nF, 25V
1
Vishay
Cc1
VJ1206A8R2KXX
Capacitor
1206
8.2pF 10%
1
Vishay
Cc2
VJ1206X102KXX
Capacitor
1206
1nF 10%
1
Vishay
Cc3
VJ1206X472KXX
Capacitor
1206
4.7nF 10%
1
Vishay
Rfadj
CRCW12063252F
Resistor
1206
32.5kΩ 1%
1
Vishay
Rc1
CRCW12065232F
Resistor
1206
52.3kΩ 1%
1
Vishay
Rc2
CRCW120662371F
Resistor
1206
2.37Ω 1%
1
Vishay
Rfb1
CRCW12062211F
Resistor
1206
2.21kΩ 1%
1
Vishay
Rfb2
CRCW12061002F
Resistor
1206
10kΩ 1%
1
Vishay
Rcs
CRCW1206202J
Resistor
1206
2kΩ 5%
1
Vishay
Table 9. Bill of Materials for Circuit of Figure 31
ID
Part Number
U1
LM2727
Q1
Si4894DY
D2
MBRS330T3
L1
SLF12565T-470M2R4
D1
MBR0520
Cin1
16MV680WG
Cinx
C3216X5R1C106M
Co1, Co2
16MV680WG
Cox
C3216X5R10J06M
Cboot
Type
Synchronous
Controller
Size
Parameters
TSSOP-14
Qty.
Vendor
1
Texas
Instruments
N-MOSFET
SO-8
30V, 15mΩ, 11.5nC
1
Vishay
Schottky Diode
SO-8
30V, 3A
1
ON
TDK
Inductor
12.5x12.8x 4.7mm
47µH, 2.7A 53mΩ
1
Schottky Diode
1812
20V 0.5A
1
ON
Al-E
1206
680µF, 16V, 1.54Arms
1
Sanyo
MLCC
1206
10µF, 16V, 3.4Arms
1
TDK
Sanyo
Al-E
D: 10mm L: 12.5mm
680µF 16V 26mΩ
2
MLCC
1206
10µF, 6.3V 2.7A
1
TDK
VJ1206X104XXA
Capacitor
1206
0.1µF, 25V
1
Vishay
Cin
C3216X7R1E225K
Capacitor
1206
2.2µF, 25V
1
TDK
Css
VJ1206X123KXX
Capacitor
1206
12nF, 25V
1
Vishay
Cc1
VJ1206A561KXX
Capacitor
1206
56pF 10%
1
Vishay
Cc2
VJ1206X392KXX
Capacitor
1206
3.9nF 10%
1
Vishay
Cc3
VJ1206X223KXX
Capacitor
1206
22nF 10%
1
Vishay
Rfadj
CRCW12062673F
Resistor
1206
267kΩ 1%
1
Vishay
Rc1
CRCW12066192F
Resistor
1206
61.9kΩ 1%
1
Vishay
Rc2
CRCW12067503F
Resistor
1206
750kΩ 1%
1
Vishay
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LM2727, LM2737
SNVS205D – AUGUST 2002 – REVISED MARCH 2013
www.ti.com
Table 9. Bill of Materials for Circuit of Figure 31 (continued)
24
ID
Part Number
Size
Parameters
Qty.
Vendor
Rfb1
CRCW12061371F
Resistor
Type
1206
1.37kΩ 1%
1
Vishay
Rfb2
CRCW12061002F
Resistor
1206
10kΩ 1%
1
Vishay
Rcs
CRCW1206122F
Resistor
1206
1.2kΩ 5%
1
Vishay
Submit Documentation Feedback
Copyright © 2002–2013, Texas Instruments Incorporated
Product Folder Links: LM2727 LM2737
LM2727, LM2737
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SNVS205D – AUGUST 2002 – REVISED MARCH 2013
REVISION HISTORY
Changes from Revision C (March 2013) to Revision D
•
Page
Changed layout of National Data Sheet to TI format .......................................................................................................... 23
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Copyright © 2002–2013, Texas Instruments Incorporated
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25
PACKAGE OPTION ADDENDUM
www.ti.com
5-Sep-2014
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
Lead/Ball Finish
MSL Peak Temp
(2)
(6)
(3)
Op Temp (°C)
Device Marking
(4/5)
LM2727MTC
NRND
TSSOP
PW
14
94
TBD
Call TI
Call TI
0 to 125
2727
MTC
LM2727MTC/NOPB
ACTIVE
TSSOP
PW
14
94
Green (RoHS
& no Sb/Br)
CU NIPDAU | CU SN
Level-1-260C-UNLIM
0 to 125
2727
MTC
LM2727MTCX/NOPB
ACTIVE
TSSOP
PW
14
2500
Green (RoHS
& no Sb/Br)
CU NIPDAU | CU SN
Level-1-260C-UNLIM
0 to 125
2727
MTC
LM2737MTC
NRND
TSSOP
PW
14
94
TBD
Call TI
Call TI
-40 to 125
2737
MTC
LM2737MTC/NOPB
ACTIVE
TSSOP
PW
14
94
Green (RoHS
& no Sb/Br)
CU NIPDAU | CU SN
Level-1-260C-UNLIM
-40 to 125
2737
MTC
LM2737MTCX
NRND
TSSOP
PW
14
2500
TBD
Call TI
Call TI
-40 to 125
2737
MTC
LM2737MTCX/NOPB
ACTIVE
TSSOP
PW
14
2500
Green (RoHS
& no Sb/Br)
CU NIPDAU | CU SN
Level-1-260C-UNLIM
-40 to 125
2737
MTC
(1)
The marketing status values are defined as follows:
ACTIVE: Product device recommended for new designs.
LIFEBUY: TI has announced that the device will be discontinued, and a lifetime-buy period is in effect.
NRND: Not recommended for new designs. Device is in production to support existing customers, but TI does not recommend using this part in a new design.
PREVIEW: Device has been announced but is not in production. Samples may or may not be available.
OBSOLETE: TI has discontinued the production of the device.
(2)
Eco Plan - The planned eco-friendly classification: Pb-Free (RoHS), Pb-Free (RoHS Exempt), or Green (RoHS & no Sb/Br) - please check http://www.ti.com/productcontent for the latest availability
information and additional product content details.
TBD: The Pb-Free/Green conversion plan has not been defined.
Pb-Free (RoHS): TI's terms "Lead-Free" or "Pb-Free" mean semiconductor products that are compatible with the current RoHS requirements for all 6 substances, including the requirement that
lead not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, TI Pb-Free products are suitable for use in specified lead-free processes.
Pb-Free (RoHS Exempt): This component has a RoHS exemption for either 1) lead-based flip-chip solder bumps used between the die and package, or 2) lead-based die adhesive used between
the die and leadframe. The component is otherwise considered Pb-Free (RoHS compatible) as defined above.
Green (RoHS & no Sb/Br): TI defines "Green" to mean Pb-Free (RoHS compatible), and free of Bromine (Br) and Antimony (Sb) based flame retardants (Br or Sb do not exceed 0.1% by weight
in homogeneous material)
(3)
MSL, Peak Temp. - The Moisture Sensitivity Level rating according to the JEDEC industry standard classifications, and peak solder temperature.
(4)
There may be additional marking, which relates to the logo, the lot trace code information, or the environmental category on the device.
Addendum-Page 1
Samples
PACKAGE OPTION ADDENDUM
www.ti.com
5-Sep-2014
(5)
Multiple Device Markings will be inside parentheses. Only one Device Marking contained in parentheses and separated by a "~" will appear on a device. If a line is indented then it is a continuation
of the previous line and the two combined represent the entire Device Marking for that device.
(6)
Lead/Ball Finish - Orderable Devices may have multiple material finish options. Finish options are separated by a vertical ruled line. Lead/Ball Finish values may wrap to two lines if the finish
value exceeds the maximum column width.
Important Information and Disclaimer:The information provided on this page represents TI's knowledge and belief as of the date that it is provided. TI bases its knowledge and belief on information
provided by third parties, and makes no representation or warranty as to the accuracy of such information. Efforts are underway to better integrate information from third parties. TI has taken and
continues to take reasonable steps to provide representative and accurate information but may not have conducted destructive testing or chemical analysis on incoming materials and chemicals.
TI and TI suppliers consider certain information to be proprietary, and thus CAS numbers and other limited information may not be available for release.
In no event shall TI's liability arising out of such information exceed the total purchase price of the TI part(s) at issue in this document sold by TI to Customer on an annual basis.
Addendum-Page 2
PACKAGE MATERIALS INFORMATION
www.ti.com
11-May-2014
TAPE AND REEL INFORMATION
*All dimensions are nominal
Device
Package Package Pins
Type Drawing
SPQ
Reel
Reel
A0
Diameter Width (mm)
(mm) W1 (mm)
B0
(mm)
K0
(mm)
P1
(mm)
W
Pin1
(mm) Quadrant
LM2727MTCX/NOPB
TSSOP
PW
14
2500
330.0
12.4
6.95
8.3
1.6
8.0
12.0
Q1
LM2737MTCX
TSSOP
PW
14
2500
330.0
12.4
6.95
8.3
1.6
8.0
12.0
Q1
LM2737MTCX/NOPB
TSSOP
PW
14
2500
330.0
12.4
6.95
8.3
1.6
8.0
12.0
Q1
Pack Materials-Page 1
PACKAGE MATERIALS INFORMATION
www.ti.com
11-May-2014
*All dimensions are nominal
Device
Package Type
Package Drawing
Pins
SPQ
Length (mm)
Width (mm)
Height (mm)
LM2727MTCX/NOPB
TSSOP
PW
14
2500
367.0
367.0
35.0
LM2737MTCX
TSSOP
PW
14
2500
367.0
367.0
35.0
LM2737MTCX/NOPB
TSSOP
PW
14
2500
367.0
367.0
35.0
Pack Materials-Page 2
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