LM5009
SNVS402I – FEBRUARY 2006 – REVISED MAY 2021
LM5009 Wide Input, 100-V,150-mA, Step-Down Switching Regulator
1 Features
3 Description
•
The LM5009 step-down switching regulator features
all of the functions needed to implement a low-cost
and efficient, buck regulator. This device is capable
of driving a 150-mA load current from a 9.5-V to 95V input source. The switching frequency can exceed
600 kHz, depending on the input and output voltages.
The output voltage can be set from 2.5 V to 85 V. This
high-voltage regulator contains an N-channel buck
switch and an internal startup regulator. The device is
easy to implement and is provided in 8-pin VSSOP
and thermally-enhanced, 8-pin WSON packages.
The regulator operation is based on a control
scheme using an on-time inversely proportional to
VIN. This feature allows the operating frequency
to remain relatively constant over load and input
voltage variations. The control scheme requires no
loop compensation, resulting in an ultrafast transient
response. An intelligent current limit is implemented
with forced off-time that is inversely proportional to
VOUT. This scheme ensures short-circuit protection
and provides minimum foldback. Other features
include thermal shutdown, VCC undervoltage lockout,
gate drive undervoltage lockout, and maximum duty
cycle limiter.
•
•
•
•
•
•
•
•
•
•
•
•
•
Newer product: LM5163 100-V, 0.5-A synchronous
buck DC/DC converter
Integrated N-channel MOSFET
150-mA output current capability
Ultra-fast transient response
No loop compensation required
VIN feedforward provides constant operating
frequency
Switching frequency can exceed 600 kHz
Highly efficient operation
2% accurate 2.5-V feedback from
–40°C to +125°C
Internal start-up regulator
Intelligent current limit protection
External shutdown control
Thermal shutdown
8-pin VSSOP and thermally enhanced 8-pin
WSON packages
2 Applications
•
•
•
•
Heat sink eliminator for classic linear regulator
applications
12-V, 24-V, 36-V, and 48-V rectified AC systems
Non-isolated AC mains charge-coupled supplies
LED current source
The new product LM5163 offers reduced BOM count,
reduced solution size, lower operating quiescent
current and many other features. Start WEBENCH®
design with LM5163.
Device Information
PART NUMBER
PACKAGE
LM5009
9. 5 - 95V
Input
VIN
BODY SIZE (NOM)
VSSOP (8)
3.00 mm × 3.00 mm
WSON (8)
4.00 mm × 4.00 mm
VCC
C3
LM5009
C1
BST
R ON
C4
RON/SD
L1
SW
VOUT
SHUTDOWN
D1
RCL
R CL
C2
R1
FB
RTN
R2
Typical Application Circuit
An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,
intellectual property matters and other important disclaimers. PRODUCTION DATA.
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Table of Contents
1 Features............................................................................1
2 Applications..................................................................... 1
3 Description.......................................................................1
4 Revision History.............................................................. 2
5 Pin Configuration and Functions...................................3
6 Specifications.................................................................. 4
6.1 Absolute Maximum Ratings........................................ 4
6.2 ESD Ratings............................................................... 4
6.3 Recommended Operating Conditions.........................4
6.4 Thermal Information....................................................4
6.5 Electrical Characteristics.............................................5
6.6 Typical Characteristics................................................ 6
7 Detailed Description........................................................7
7.1 Overview..................................................................... 7
7.2 Functional Block Diagram........................................... 7
7.3 Feature Description.....................................................7
7.4 Device Functional Modes..........................................10
8 Application and Implementation.................................. 11
8.1 Application Information..............................................11
8.2 Typical Application.................................................... 11
8.3 Do's and Don'ts.........................................................16
9 Power Supply Recommendations................................16
10 Layout...........................................................................17
10.1 Layout Guidelines................................................... 17
10.2 Layout Example...................................................... 17
11 Device and Documentation Support..........................18
11.1 Documentation Support.......................................... 18
11.2 Receiving Notification of Documentation Updates.. 18
11.3 Support Resources................................................. 18
11.4 Trademarks............................................................. 18
11.5 Electrostatic Discharge Caution.............................. 18
11.6 Glossary.................................................................. 18
12 Mechanical, Packaging, and Orderable
Information.................................................................... 18
4 Revision History
NOTE: Page numbers for previous revisions may differ from page numbers in the current version.
Changes from Revision H (October 2015) to Revision I (May 2021)
Page
• Added information for LM5163 promotion.......................................................................................................... 1
• Updated the numbering format for tables, figures, and cross-references throughout the document. ................1
• Changed Section 2 bullets..................................................................................................................................1
• Changed Section 3, editorial...............................................................................................................................1
Changes from Revision G (February 2013) to Revision H (October 2015)
Page
• Added ESD Ratings table, Feature Description section, Device Functional Modes, Application and
Implementation section, Power Supply Recommendations section, Layout section, Device and
Documentation Support section, and Mechanical, Packaging, and Orderable Information section. ................. 1
Changes from Revision F (February 2013) to Revision G (February 2013)
Page
• Changed layout of National Data Sheet to TI format........................................................................................ 16
2
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5 Pin Configuration and Functions
1
8
SW
VIN
BST
VCC
RCL
RON/SD
RTN
FB
2
3
7
6
4
5
Figure 5-1. DGK, NGU Packages 8-Pin VSSOP, WSON Top View
Table 5-1. Pin Functions
PIN
NAME
NO.
I/O
DESCRIPTION
Boost pin. An external capacitor is required between the BST and SW pins. A 0.022-µF
ceramic capacitor is recommended. An internal diode charges the capacitor from VCC.
BST
2
I
EP
—
—
Exposed pad (WSON package only). Exposed metal pad on the underside of the device.
Connecting this pad to the PC board ground plane is recommended to aid in heat
dissipation.
FB
5
I
Feedback input from regulated output. This pin is connected to the inverting input of the
internal regulation comparator. The regulation threshold is 2.5 V.
RCL
3
I
Current limit off-time set pin. A resistor between this pin and RTN sets the off-time when
current limit is detected. The off-time is preset to 35 µs if FB = 0 V.
RON/SD
6
I
On-time set pin. A resistor between this pin and VIN sets the switch on-time as a function of
VIN. The minimum recommended on-time is 250 ns at the maximum input voltage. This pin
can be used for remote shutdown.
RTN
4
—
Ground pin. Ground for the entire circuit.
SW
1
O
Switching output. Power switching output. Connect to the inductor, recirculating diode, and
bootstrap capacitor.
VCC
7
O
Output from the internal high-voltage startup regulator. Regulated at 7.0 V. If an auxiliary
voltage is available to raise the voltage on this pin above the regulation set point (7 V), the
internal series pass regulator shuts down, reducing the device power dissipation. Do not
exceed 14 V. This voltage provides gate drive power for the internal buck switch. An internal
diode is provided between this pin and the BST pin. A local 0.1-µF decoupling capacitor is
required.
VIN
8
I
Input voltage. Recommended operating range: 9.5 V to 95 V.
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6 Specifications
6.1 Absolute Maximum Ratings
over operating free-air temperature range (unless otherwise noted)(1)
MIN
MAX
UNIT
VIN to RTN
–0.3
100
V
BST to RTN
–0.3
114
V
SW to RTN (steady-state)
–1
V
BST to VCC
100
V
BST to SW
14
V
VCC to RTN
14
V
All other inputs to RTN
–0.3
7
V
Storage temperature, Tstg
–65
150
°C
(1)
Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress
ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under
Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device
reliability.
6.2 ESD Ratings
VALUE
V(ESD)
(1)
(2)
(3)
Electrostatic discharge
Human-body model (HBM), per ANSI/ESDA/JEDEC
JS-001(1) (3)
UNIT
±2000
Charged-device model (CDM), per JEDEC specification JESD22-C101(2)
V
±750
JEDEC document JEP155 states that 500-V HBM allows safe manufacturing with a standard ESD control process.
JEDEC document JEP157 states that 250-V CDM allows safe manufacturing with a standard ESD control process.
The human body model is a 100-pF capacitor discharged through a 1.5-kΩ resistor into each pin.
6.3 Recommended Operating Conditions
over operating free-air temperature range (unless otherwise noted)(1)
MIN
VIN
(1)
MAX
UNIT
Line voltage
9.5
95
V
Operating junction temperature
–40
125
°C
Operating ratings are conditions under which operation of the device is intended to be functional. For specifications and test conditions,
see the Section 6.5.
6.4 Thermal Information
LM5009
THERMAL METRIC(1)
NGU (WSON)
UNIT
8 PINS
8 PINS
RθJA
Junction-to-ambient thermal resistance
157.7
42.8
°C/W
RθJC(top)
Junction-to-case (top) thermal resistance
50.2
41.5
°C/W
RθJB
Junction-to-board thermal resistance
77.9
20.1
°C/W
ψJT
Junction-to-top characterization parameter
4.5
0.4
°C/W
ψJB
Junction-to-board characterization parameter
76.5
20.2
°C/W
RθJC(bot)
Junction-to-case (bottom) thermal resistance
n/a
4.5
°C/W
(1)
4
DGK (VSSOP)
For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application
report, SPRA953.
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6.5 Electrical Characteristics
Typical limits are for TJ = 25°C only, and all maximum and minimum limits apply over the junction temperature (TJ) range of
–40°C to +125°C. Minimum and maximum limits are specified through test, design, or statistical correlation. Typical values
represent the most likely parametric norm at TJ = 25°C, and are provided for reference purposes only. Unless otherwise
stated, the following conditions apply: VIN = 48 V and RON = 200 kΩ.(1).
PARAMETER
TEST CONDITIONS
MIN
TYP
MAX
6.6
7
7.4
UNIT
VCC SUPPLY
VCC reg
VCC regulator output
VCC current
limit(2)
V
9.5
mA
VCC undervoltage lockout voltage
(VCC increasing)
6.3
V
VCC undervoltage hysteresis
200
mV
VCC UVLO delay (filter)
100-mV overdrive
IIN operating current
Non-switching, FB = 3 V
IIN shutdown current
10
µs
485
675
µA
RON/SD = 0 V
76
150
µA
Buck switch Rds(on)
ITEST = 200 mA(3)
2.0
4.4
Ω
Gate drive UVLO
VBST − VSW rising
4.5
5.5
SWITCH CHARACTERISTICS
3.4
Gate drive UVLO hysteresis
430
V
mV
CURRENT LIMIT
Current limit threshold
0.25
Current limit response time
Iswitch overdrive = 0.1-A time to switch off
OFF time generator (test 1)
FB = 0 V, RCL = 100 kΩ
OFF time generator (test 2)
FB = 2.3 V, RCL = 100 kΩ
0.31
0.37
A
400
ns
35
µs
2.56
µs
ON TIME GENERATOR
TON - 1
VIN = 10 V, RON = 200 kΩ
2.15
2.77
3.5
µs
TON - 2
VIN = 95 V, RON = 200 kΩ
200
300
420
ns
Remote shutdown threshold
Rising
0.4
0.7
1.05
Remote shutdown hysteresis
V
35
mV
300
ns
MINIMUM OFF TIME
Minimum off timer
FB = 0 V
REGULATION AND OV COMPARATORS
FB reference threshold
Internal reference, trip point for switch on
FB overvoltage threshold
Trip point for switch off
FB bias current
2.445
2.5
2.550
V
2.875
V
1
nA
165
°C
25
°C
THERMAL SHUTDOWN
Tsd
Thermal shutdown temperature
Thermal shutdown hysteresis
(1)
(2)
(3)
All electrical characteristics having room temperature limits are tested during production with TA = TJ = 25°C. All hot and cold limits are
specified by correlating the electrical characteristics to process and temperature variations and applying statistical process control.
The VCC output is intended as a self bias for the internal gate drive power and control circuits. Device thermal limitations limit external
loading.
For devices procured in the WSON-8 package, the Rds(on) limits are specified by design characterization data only.
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6.6 Typical Characteristics
10
7.1
FS = 180 kHz
6.9
Ron = 500k
VCC (V)
ON-TIME (Ps)
7.0
1.0
300k
400 kHz
6.8
725 kHz
1.2 MHz
6.7
100k
6.6
0.1
0
20
40
60
80
6.5
9.0
100
9.5
10.0
VIN (V)
Figure 6-2. VCC vs VIN and FS
35
8
30
7
VIN t 15V
VIN = 9.5V
6
25
RCL = 500k
10V
5
20
VCC (V)
CURRENT LIMIT OFF TIME (Ps)
Figure 6-1. On-Time vs VIN and RON
15
4
3
300k
10
11.0
10.5
VIN (V)
2
100k
5
1
50k
0
0
0
0.5
1.0
1.5
2.0
0
2.5
2
VFB (V)
4
6
8
10
ICC (mA, External Load)
Figure 6-3. Current Limit Off-Time vs VFB and RCL
Figure 6-4. VCC vs ICC and VIN
4.0
ICC INPUT CURRENT (mA)
3.5
FS = 1.2 MHz
3.0
FS = 725 kHz
2.5
FS = 400 kHz
2.0
1.5
1.0
FS = 180 kHz
0.5
0
8
9
10
11
12
13
14
EXTERNALLY APPLIED VCC (V)
Figure 6-5. ICC Current vs Applied VCC Voltage
6
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7 Detailed Description
7.1 Overview
The LM5009 step-down switching regulator features all the functions needed to implement a low-cost, efficient,
buck bias power converter. This high-voltage regulator contains a 100-V N-channel buck switch, is easy to
implement, and is provided in VSSOP-8 and thermally-enhanced, WSON-8 packages. The regulator is based
on a control scheme using an on-time inversely proportional to VIN. The control scheme requires no loop
compensation. Current limit is implemented with forced off-time that is inversely proportional to VOUT. This
scheme ensures short-circuit protection and provides minimum foldback. The functional block diagram of the
LM5009 is shown in the Section 7.2 section.
The LM5009 can be applied in numerous applications to efficiently regulate down higher voltages. This regulator
is well-suited for 48-V telecom and 42-V automotive power bus ranges. Additional features include: thermal
shutdown, VCC undervoltage lockout, gate drive undervoltage lockout, maximum duty cycle limit timer, and the
intelligent current limit off timer.
7.2 Functional Block Diagram
7V SERIES
REGULATOR
9.5V - 95V
Input
LM5009
VCC
8
VIN
C1
C5
ON TIMER
START
COMPLETE
6
SD/
RON
SHUTDOWN
BST
Ron
OVER-VOLTAGE
COMPARATOR
+
-
2.875V
START
UVLO
MINIMUM
OFF-TIMER
FB
FB
3
RCL
S
REGULATION
COMPARATOR
R
SET
CLR
L1
SW 1
VOUT1
Q
Q
R1
COMPLETE
RCL
START
CURRENT LIMIT
OFF TIMER
RCL
C4
DRIVER
LEVEL
SHIFT
+
-
5
2
VIN
SD
COMPLETE
2.5V
4
C3
THERMAL
SHUTDOWN
UVLO
RON
7
SD
+
0.31A
BUCK
SWITCH
CURRENT
SENSE
R3
VOUT2
D1
RTN
R2
C2
7.3 Feature Description
7.3.1 Control Circuit Overview
The LM5009 is a buck dc-dc regulator that uses a control scheme where the on-time varies inversely with line
voltage (VIN). Control is based on a comparator and the on-time one-shot, with the output voltage feedback (FB)
compared to an internal reference (2.5 V). If the FB level is below the reference, then the buck switch is turned
on for a fixed time determined by the line voltage and a programming resistor (RON). Following the on period, the
switch remains off for at least the minimum off-timer period of 300 ns. If FB is still below the reference at that
time, then the switch turns on again for another on-time period. This cycle continues until regulation is achieved,
at which time the off-time increases based on the required duty cycle.
The LM5009 operates in discontinuous conduction mode at light load currents, and continuous conduction mode
at heavy load current. In discontinuous conduction mode, current through the output inductor starts at zero
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and ramps up to a peak during the on-time, then ramps back to zero before the end of the off-time. The next
on-time period starts when the voltage at FB falls below the internal reference—until then, the inductor current
remains zero. In this mode the operating frequency is lower than in continuous conduction mode, and varies
with load current. Therefore, at light loads the conversion efficiency is maintained because the switching losses
reduce with the reduction in load and frequency. The discontinuous operating frequency can be calculated as by
Equation 1:
VOUT2 x L x 1.28 x 1020
F=
RL x (RON)2
(1)
where
•
RL = the load resistance
In continuous conduction mode, current flows continuously through the inductor and never ramps down to zero.
In this mode, the operating frequency is greater than the discontinuous mode frequency and remains relatively
constant with load and line variations. The approximate continuous mode operating frequency can be calculated
by Equation 2:
VOUT
F=
1.25 x 10-10 x RON
(2)
The output voltage (VOUT) is programmed by two external resistors; see the Section 7.2 section. The regulation
point is calculated by Equation 3:
VOUT = 2.5 × (R1 + R2) / R2
(3)
This regulator regulates the output voltage based on ripple voltage at the feedback input, requiring a minimum
amount of equivalent series resistance (ESR) for the output capacitor C2. A minimum of 25 mV of ripple voltage
at the feedback pin (FB) is required for the LM5009. In cases where the capacitor ESR is too small, additional
series resistance may be required (see R3 in the Section 7.2 section).
For applications where lower output voltage ripple is required, the output can be taken directly from a low-ESR
output capacitor, as shown in Figure 7-1. However, R3 slightly degrades the load regulation.
L1
SW
LM5009
R1
R3
FB
VOUT2
R2
C2
Figure 7-1. Low Ripple Output Configuration
7.3.2 High Voltage Startup Regulator
The LM5009 contains an internal high voltage startup regulator. The input pin (VIN) can be connected directly to
line voltages up to 95 V, with transient capability to 100 V. The regulator is internally current limited at 9.5 mA.
Upon power-up, the regulator sources current into the external capacitor at VCC (C3). When the voltage on the
VCC pin reaches the undervoltage lockout threshold of 6.3 V, the buck switch is enabled.
8
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In applications involving a high value for VIN, where power dissipation in the VCC regulator is a concern, an
auxiliary voltage can be diode connected to the VCC pin. Setting the voltage between 8 V and 14 V shuts off the
internal regulator, reducing internal power dissipation, as shown in Figure 7-2. The current required into the VCC
pin is illustrated in the Section 6.6 section.
VCC
C3
BST
C4
LM5009
L1
D2
SW
VOUT1
D1
R1
R3
R2
C2
FB
Figure 7-2. Self-Biased Configuration
7.3.3 Regulation Comparator
The feedback voltage at FB is compared to an internal 2.5-V reference. In normal operation (the output voltage
is regulated), an on-time period is initiated when the voltage at FB falls below 2.5 V. The buck switch stays on for
the programmed on-time, causing the FB voltage to rise above 2.5 V. After the on-time period, the buck switch
stays off until the FB voltage again falls below 2.5 V. During start-up, the FB voltage is below 2.5 V at the end of
each on-time, resulting in the minimum off-time. Bias current at the FB pin is less than 5 nA over temperature.
7.3.4 Overvoltage Comparator
The feedback voltage at FB is compared to an internal 2.875-V reference. If the voltage at FB rises above 2.875
V, then the on-time pulse is immediately terminated. This condition can occur if the input voltage, or the output
load, changes suddenly. The buck switch does not turn on again until the voltage at FB falls below 2.5 V.
7.3.5 On-Time Generator
The on-time for the LM5009 is determined by the RON resistor, and is inversely proportional to the input voltage
(VIN), resulting in a nearly constant frequency because VIN is varied over its range. The on-time equation is
shown in Equation 4:
TON = 1.25 × 10–10 × RON / VIN
(4)
Select RON for a minimum on-time (at maximum VIN) greater than 250 ns, for proper current limit operation. This
requirement limits the maximum frequency for each application, depending on VIN and VOUT.
7.3.6 Current Limit
The LM5009 contains an intelligent current limit off timer. If the current in the buck switch exceeds 0.31 A, then
the present cycle is immediately terminated and a non-resettable off timer is initiated. The length of off-time is
controlled by an external resistor (RCL) and the FB voltage. When FB = 0 V, a maximum off-time is required and
the time is preset to 35 µs. This condition occurs when the output is shorted and during the initial part of start-up.
This amount of time ensures safe short-circuit operation up to the maximum input voltage of 95 V. In cases of
overload where the FB voltage is above 0 V (not a short-circuit) the current limit off-time is less than 35 µs.
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Reducing the off-time during less severe overloads reduces the amount of foldback, recovery time, and start-up
time. The off-time is calculated from Equation 5:
10
TOFF =
-5
VFB
0.285 +
-6
(6.35 x 10 x RCL)
(5)
The current limit sensing circuit is blanked for the first 50 ns to 70 ns of each on-time so it is not falsely tripped
by the current surge that occurs at turn-on. The current surge is required by the recirculating diode (D1) for its
turn-off recovery.
7.3.7 N-Channel Buck Switch and Driver
The LM5009 integrates an N-channel buck switch and associated floating high-voltage gate driver. The gate
driver circuit works in conjunction with an external bootstrap capacitor and an internal high-voltage diode. A
0.022‑µF ceramic capacitor (C4) connected between the BST pin and SW pin provides the voltage to the driver
during the on-time.
During each off-time, the SW pin is at approximately –1 V, and the bootstrap capacitor charges from VCC through
the internal diode. The minimum off timer ensures a minimum time for each cycle to recharge the bootstrap
capacitor.
An external re-circulating diode (D1) carries the inductor current after the internal buck switch turns off. This
diode must be of the ultra-fast or Schottky type to minimize turn-on losses and current overshoot.
7.3.8 Thermal Protection
Operate the LM5009 so that the junction temperature does not exceed 125°C during normal operation. An
internal thermal shutdown circuit is provided to protect the LM5009 in the event of a higher than normal junction
temperature. When activated, typically at 165°C, the controller is forced into a low-power reset state, disabling
the buck switch. This feature prevents catastrophic failures from accidental device overheating. When the
junction temperature reduces below 140°C (typical hysteresis = 25°C), the buck switch is enabled and normal
operation is resumed.
7.4 Device Functional Modes
The LM5009 can be remotely disabled by taking the RON/SD pin to ground, as shown in Figure 7-3. The voltage
at the RON/SD pin is between 1.7 V and 5 V, depending on VIN and the value of the RON resistor.
Input
Voltage
VIN
RON
LM5009
RON/SD
STOP
RUN
Figure 7-3. Shutdown Implementation
10
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8 Application and Implementation
Note
Information in the following applications sections is not part of the TI component specification,
and TI does not warrant its accuracy or completeness. TI’s customers are responsible for
determining suitability of components for their purposes, as well as validating and testing their design
implementation to confirm system functionality.
8.1 Application Information
The LM5009 is a non-synchronous buck regulator designed to operate over a wide input voltage range and
output current. Spreadsheet-based quick-start calculation tools and the on-line WEBENCH® software can be
used to create a buck design along with the bill of materials, estimated efficiency, and the complete solution cost.
8.2 Typical Application
A typical buck application circuit with the LM5009 is shown in Figure 8-1. The circuit can operate over a wide
input voltage range of 9.5 V to 95 V and provides a stable output of 10 V over the load current being varied from
50 mA to 200 mA. The resulting curves are shown in Figure 8-2 through Figure 8-5.
9. 5 - 95V
Input
VIN
VCC
C3
LM5009
C1
BST
R ON
C4
RON/SD
L1
SW
VOUT
SHUTDOWN
D1
RCL
R CL
C2
R1
FB
RTN
R2
Figure 8-1. Typical Buck Application Circuit
8.2.1 Design Requirements
A typical buck application circuit with the LM5009 can be summarized by the operating conditions listed in Table
8-1.
Table 8-1. Design Parameters
DESIGN PARAMETER
EXAMPLE VALUE
Input voltage range
9.5 V to 95 V
Output voltage
10 V
Load current range
50 mA to 200 mA
Nominal switching frequency
330 kHz
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8.2.2 Detailed Design Procedure
8.2.2.1 Output Resistor Divider Selection
R1 and R2: From the Section 7.2 section, VOUT1 can be determined to be equal to VFB × (R1 + R2) / R2, and
because V FB = 2.5 V, the ratio of R1 to R2 calculates as 3:1. Standard values of 3.01 kΩ (R1) and 1.00 kΩ (R2)
are chosen. Other values can be used as long as the 3:1 ratio is maintained. The selected values, however,
provide a small amount of output loading (2.5 mA) in the event that the main load is disconnected and allows the
circuit to maintain regulation until the main load is reconnected.
8.2.2.2 Frequency Selection
Fs and RON: Unless the application requires a specific frequency, the choice of frequency is generally a
compromise because the size of L1 and C2, and the switching losses are affected. The maximum-allowed
frequency, based on a minimum on-time of 250 ns, is calculated by Equation 6:
FMAX = VOUT / (VINMAX × 250 ns)
(6)
For this exercise, FMAX = 444 kHz. From Equation 2, RON calculates to 180 kΩ. A standard-value, 237-kΩ
resistor is used to allow for tolerances in Equation 2, resulting in a nominal frequency of 337 kHz.
8.2.2.3 Inductor Selection
L1: The main parameter affected by the inductor is the output current ripple amplitude. The choice of inductor
value therefore depends on both the minimum and maximum load currents, keeping in mind that the maximum
ripple current occurs at maximum VIN.
1. Minimum load current: To maintain continuous conduction at minimum IO (100 mA), the ripple amplitude
(IOR) must be less than 200 mA peak-to-peak so the lower peak of the waveform does not reach zero. L1 is
calculated using Equation 7:
VOUT1 x (VIN - VOUT1)
L1 =
IOR x Fs x VIN
(7)
At VIN = 90 V, L1 (min) calculates to 132 µH. The next larger standard value (150 µH) is chosen and, with
this value, IOR calculates to 176 mA peak-to-peak at VIN = 90 V and 33 mA peak-to-peak at VIN = 12 V.
2. Maximum load current: At a load current of 150 mA, the peak of the ripple waveform must not reach the
minimum value of the LM5009 current limit threshold (250 mA). Therefore, the ripple amplitude must be less
than 200 mA peak-to-peak, which is already satisfied in Equation 7. With L1 = 150 µH, at maximum VIN
and IO, the peak of the ripple is 238 mA. Although L1 must carry this peak current without saturating or
exceeding its temperature rating, L1 must also be capable of carrying the maximum value of the LM5009
current limit threshold (370 mA) without saturating because the current limit is reached during startup.
8.2.2.4 VCC and Bootstrap Capacitor
C3: The capacitor on the VCC output provides not only noise filtering and stability, but also prevents false
triggering of the VCC UVLO at the buck switch on and off transitions. For this reason, C3 must be no smaller than
0.1 µF.
C4: The recommended value is 0.022 µF for C4 because this value is appropriate in the majority of applications.
A high-quality ceramic capacitor, with low ESR is recommended because C4 supplies the surge current to
charge the buck switch gate at turn-on. A low ESR also ensures a quick recharge during each off-time. At
minimum VIN when the on-time is at maximum, C4 can possibly not fully recharge at start-up during each 300-ns
off-time. This failure to recharge results from the circuit being unable to complete the start-up and achieve output
regulation. This condition can occur when the frequency is intended to be low (for example, RON = 500 kΩ). In
this case, increase C4 to maintain sufficient voltage across the buck switch driver during each on-time.
12
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8.2.2.5 Output Capacitor Selection
C2 and R3: When selecting the output filter capacitor C2, the items to consider are ripple voltage resulting from
the C2 ESR, ripple voltage resulting from the C2 capacitance, and the nature of the load.
1. ESR and R3: A low ESR for C2 is generally desirable to minimize power losses and heating within the
capacitor. However, this regulator requires a minimum amount of ripple voltage at the feedback input for
proper loop operation. For the LM5009, the minimum ripple required at pin 5 is 25 mV peak-to-peak,
requiring a minimum ripple at VOUT1 of 100 mV. The minimum ESR required at VOUT1 is 3 Ω because the
minimum ripple current (at minimum VIN) is 33 mA peak-to-peak. R3 is inserted as illustrated in the Section
7.2 section because quality capacitors for SMPS applications have considerably less ESR. The value of R3,
along with the ESR of C2, must result in at least a 25-mV peak-to-peak ripple at pin 5. Generally, R3 is 0.5 Ω
to 5.0 Ω.
2. Nature of the load: The load can be connected to VOUT1 or VOUT2. VOUT1 provides good regulation, but with
a ripple voltage that ranges from 100 mV (at VIN = 12 V) to 580 mV (at VIN = 90 V). Alternatively, VOUT2
provides low ripple (3 mV to 13 mV) but lower regulation resulting from R3.
C2 generally must be no smaller than 3.3 µF. Typically, the value of C2 is 10 µF to 20 µF, with the optimum
value determined by the load. If the load current is fairly constant, a small value suffices for C2. If the load
current includes significant transients, a larger value is necessary. For each application, experimentation is
needed to determine the optimum values for R3 and C2.
3. Ripple reduction: The ripple amplitude at VOUT1 can be reduced by reducing R3 and by adding a capacitor
across R1 to transfer the ripple at VOUT1 directly to the FB pin without attenuation. The new value of R3 is
calculated by Equation 8:
R3 = 25 mV / IOR(min)
(8)
where
•
IOR(min) is the minimum ripple current amplitude—33 mAp-p in this example
The added capacitor value is calculated by Equation 9:
C = TON(max) / (R1 // R2)
(9)
where
•
TON(max) is the maximum on-time (at minimum VIN)
The selected capacitor must be larger than the value calculated in Equation 9.
8.2.2.6 Current Limit Off-Timer Setting
RCL: When a current limit condition is detected, the minimum off-time set by this resistor must be greater than
the maximum normal off-time that occurs at maximum VIN. Using Equation 4, the minimum on-time is 0.329 µs,
yielding a maximum off-time of 2.63 µs. This value is further increased by 82 ns (to 2.72 µs), resulting from a
±25% tolerance of the on-time. This value is then increased to allow for the response time of the current limit
detection loop (400 ns).
The off-time determined by Equation 5 has a ±25% tolerance, as given by Equation 10:
tOFFCL(MIN) = (2.72 µs × 1.25) + 0.4 µs = 3.8 µs
(10)
Using Equation 5, RCL calculates to 167 kΩ (at VFB = 2.5 V). The closest standard value is 169 kΩ.
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8.2.2.7 Rectifier Diode Selection
D1: The important parameters are reverse recovery time and forward voltage. Reverse recovery time determines
how long the reverse current surge lasts each time that the buck switch is turned on. The forward voltage drop
is significant in the event that the output is short-circuited because only this diode voltage forces the inductor
current to reduce during the forced off-time. For this reason, a higher voltage is better, although higher voltages
affect efficiency. A good choice is an ultrafast or Schottky diode with a reverse recovery time of approximately 30
ns and a forward voltage drop of approximately 0.7 V. Other types of diodes can have a lower forward voltage
drop, but can also have longer recovery times or greater reverse leakage. The D1 reverse voltage rating must be
at least as great as the maximum VIN, and the D1 current rating must be greater than the maximum current limit
threshold (370 mA).
8.2.2.8 Input Capacitor Selection
C1: The purpose of this capacitor is to supply most of the switch current during the on-time and to limit the
voltage ripple at VIN, on the assumption that the voltage source feeding VIN has an output impedance greater
than zero. At maximum load current, when the buck switch turns on, the current into pin 8 suddenly increases to
the lower peak of the output current waveform, ramps up to the peak value, and then drops to zero at turn-off.
The average input current during this on-time is the load current (150 mA). For a worst-case calculation, C1 must
supply this average load current during the maximum on-time. To keep the input voltage ripple to less than 2 V
(for this exercise), C1 calculates to Equation 11:
I x tON
C1 =
'V
=
0.15A x 2.47 Ps
2.0V
= 0.185 PF
(11)
Quality ceramic capacitors in this value have a low ESR that adds only a few millivolts to the ripple. The
capacitance is dominant in this case. To allow for the capacitor tolerance, temperature effects, and voltage
effects, a 1.0-µF, 100-V, X7R capacitor is used.
C5: This capacitor helps avoid supply voltage transients and ringing resulting from long lead inductance at VIN.
A low-ESR, 0.1-µF ceramic chip capacitor is recommended, located close to the LM5009.
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8.2.2.9 Ripple Configuration
The LM5009 uses a constant-on-time (COT) control scheme where the on-time is terminated by a one-shot
and the off-time is terminated by the feedback voltage (VFB) falling below the reference voltage. Therefore, for
stable operation, the feedback voltage must decrease monotonically in phase with the inductor current during the
off-time. Furthermore, this change in feedback voltage (VFB) during off-time must be large enough to dominate
any noise present at the feedback node.
Table 8-2 presents three different methods for generating appropriate voltage ripple at the feedback node. Type
1 and type 2 ripple circuits couple the ripple from the output of the converter to the feedback node (FB). The
output voltage ripple has two components:
1. Capacitive ripple caused by the inductor current ripple charging or discharging the output capacitor.
2. Resistive ripple caused by the inductor current ripple flowing through the ESR of the output capacitor and
R3.
Table 8-2. Ripple Configuration
TYPE 1
TYPE 2
Lowest cost
TYPE 3
Reduced ripple
VOUT
Minimum ripple
VOUT
L1
VOUT
L1
L1
R FB2
Cff
R FB2
R3
To FB
RA
R3
R FB2
CB
To FB
GND
C OUT
C OUT
R FB1
To FB
R FB1
GND
25 mV u VO
R3 t
VREF u 'IL1, min
COUT
CA
R FB1
GND
Cff t
(12)
5
FSW u (RFB2 IIRFB1 )
25 mV
R3 t
'IL1, min
R A CA t
(VIN, min
VO ) u TON(@ VIN, min )
25mV
(14)
(13)
The capacitive ripple is out of phase with the inductor current. As a result, the capacitive ripple does not
decrease monotonically during the off-time. The resistive ripple is in phase with the inductor current and
decreases monotonically during the off-time. The resistive ripple must exceed the capacitive ripple at output
(VOUT) for stable operation. If this condition is not satisfied, then unstable switching behavior is observed in COT
converters with multiple on-time bursts in close succession followed by a long off-time.
The type 3 ripple method uses a ripple injection circuit with RA, CA, and the switch node (SW) voltage to
generate a triangular ramp. This triangular ramp is then ac-coupled into the feedback node (FB) using the
capacitor CB. This circuit is suited for applications where low output voltage ripple is imperative because this
circuit does not use the output voltage ripple. See application note AN-1481 Controlling Output Ripple and
Achieving ESR Independence in Constant On-Time (COT) Regulator Designs, SNVA166 for more details on
each ripple generation method.
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8.2.3 Application Curves
100
100
Vin = 12V
EFFICIENCY (%)
EFFICIENCY (%)
80
Vin = 48V
70
IOUT = 200 mA
90
90 Vin = 30V
Vin = 90V
80
IOUT = 100 mA
70
60
60
50
50
100
150
50
200
0
20
LOAD CURRENT (mA)
60
80
100
VIN (V)
Figure 8-2. Efficiency vs Load Current and VIN
Figure 8-3. Efficiency vs VIN and Load Current
330
LOAD CURRENT @ CURRENT LIMIT
ONSET (mA)
10.4
10.2
VOUT (V)
40
10.0
9.8
9.6
Vin = 48V
9.4
310
290
270
250
230
50
100
150
200
0
LOAD CURRENT (mA)
20
40
60
80
100
VIN (V)
Figure 8-4. VOUT vs Load Current
Figure 8-5. Current Limit vs VIN
8.3 Do's and Don'ts
A minimum load current of 1 mA is required to maintain proper operation. If the load current falls below that level,
the bootstrap capacitor can discharge during the long off-time and the circuit either shuts down or cycles on and
off at a low frequency. If the load current is expected to drop below 1 mA in the application, choose the feedback
resistors to be low enough in value to provide the minimum required current at nominal VOUT.
9 Power Supply Recommendations
The LM5009 is designed to operate with an input power supply capable of supplying a voltage range between
9 V and 95 V. The input power supply must be well-regulated and capable of supplying sufficient current to the
regulator during peak load operation. Also, like in all applications, the power-supply source impedance must be
small compared to the module input impedance to maintain the stability of the converter.
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10 Layout
10.1 Layout Guidelines
The LM5009 regulation and overvoltage comparators are very fast, and as such respond to short-duration noise
pulses. Layout considerations are therefore critical for optimum performance. The components at pins 1, 2, 3, 5,
and 6 must be as physically close as possible to the device, thereby minimizing noise pickup in the PC tracks.
The two major current loops conduct currents that switch very fast and, therefore, those loops must be as small
as possible to minimize conducted and radiated electromagnetic interference (EMI). The first loop is formed by
CIN, through the VIN to SW pins, LIND, COUT, and back to CIN. The second current loop is formed by D1, LIND,
and COUT.
If the internal dissipation of the LM5009 produces excessive junction temperatures during normal operation,
good use of the PC board ground plane can help considerably to dissipate heat. The exposed pad on the
bottom of the WSON-8 package can be soldered to a ground plane on the PC board, and that plane must
extend out from beneath the device to help dissipate heat. Additionally, the use of wide PC board traces, where
possible, can also help conduct heat away from the device. Judicious positioning of the PC board within the end
product, along with the use of any available air flow (forced or natural convection) can help reduce the junction
temperatures.
10.2 Layout Example
VOUT
CA
COUT
LIND
D1
GND
Cbyp
RA
CIN
SW
SW
LM5009
VIN
VLINE
CBST
VCC
BST
Exp Thermal
Pad
RON
RCL
RON
RTN
FB
CVCC
RFB2
GND
CB
RFB1
Via to Ground Plane
Figure 10-1. LM5009 Buck Layout Example with the WSON Package
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11 Device and Documentation Support
11.1 Documentation Support
11.1.1 Related Documentation
Application note AN-1481 Controlling Output Ripple and Achieving ESR Independence in Constant On-Time
(COT) Regulator Designs, SNVA166
11.2 Receiving Notification of Documentation Updates
To receive notification of documentation updates, navigate to the device product folder on ti.com. Click on
Subscribe to updates to register and receive a weekly digest of any product information that has changed. For
change details, review the revision history included in any revised document.
11.3 Support Resources
TI E2E™ support forums are an engineer's go-to source for fast, verified answers and design help — straight
from the experts. Search existing answers or ask your own question to get the quick design help you need.
Linked content is provided "AS IS" by the respective contributors. They do not constitute TI specifications and do
not necessarily reflect TI's views; see TI's Terms of Use.
11.4 Trademarks
TI E2E™ is a trademark of Texas Instruments.
is a registered trademark of TI.
All trademarks are the property of their respective owners.
11.5 Electrostatic Discharge Caution
This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled
with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.
ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may
be more susceptible to damage because very small parametric changes could cause the device not to meet its published
specifications.
11.6 Glossary
TI Glossary
This glossary lists and explains terms, acronyms, and definitions.
12 Mechanical, Packaging, and Orderable Information
The following pages include mechanical, packaging, and orderable information. This information is the most
current data available for the designated devices. This data is subject to change without notice and revision of
this document. For browser-based versions of this data sheet, refer to the left-hand navigation.
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30-Sep-2021
PACKAGING INFORMATION
Orderable Device
Status
(1)
Package Type Package Pins Package
Drawing
Qty
Eco Plan
(2)
Lead finish/
Ball material
MSL Peak Temp
Op Temp (°C)
Device Marking
(3)
(4/5)
(6)
LM5009MM
NRND
VSSOP
DGK
8
1000
Non-RoHS
& Green
Call TI
Level-1-260C-UNLIM
-40 to 125
SLLB
LM5009MM/NOPB
ACTIVE
VSSOP
DGK
8
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
SLLB
LM5009MMX/NOPB
ACTIVE
VSSOP
DGK
8
3500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
SLLB
LM5009SDC/NOPB
ACTIVE
WSON
NGU
8
1000
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
5009SD
LM5009SDCX/NOPB
ACTIVE
WSON
NGU
8
4500
RoHS & Green
SN
Level-1-260C-UNLIM
-40 to 125
5009SD
(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)
RoHS: TI defines "RoHS" to mean semiconductor products that are compliant with the current EU RoHS requirements for all 10 RoHS substances, including the requirement that RoHS substance
do not exceed 0.1% by weight in homogeneous materials. Where designed to be soldered at high temperatures, "RoHS" products are suitable for use in specified lead-free processes. TI may
reference these types of products as "Pb-Free".
RoHS Exempt: TI defines "RoHS Exempt" to mean products that contain lead but are compliant with EU RoHS pursuant to a specific EU RoHS exemption.
Green: TI defines "Green" to mean the content of Chlorine (Cl) and Bromine (Br) based flame retardants meet JS709B low halogen requirements of