www.ti.com

Table of Contents

Application NoteOptimizing Line and Load Regulation in Automotive, 48-V
Battery and eBike Applications

Marshall Beck
ABSTRACT
Higher voltage batteries are becoming more prevalent in automotive and eBike applications. The extended
VIN range is causing designers to examine more closely the line regulation of the pre-regulator. Furthermore,
the pre-regulator might need to support a no load to full load condition, so load regulation is also of highimportance. This application note reviews line and load regulation for 48-V battery and eBike, pre-regulators
using LM5013-Q1 as an example.

Table of Contents
1 Introduction.............................................................................................................................................................................22 Overview of COT.....................................................................................................................................................................23 Line Regulation.......................................................................................................................................................................34 Load Regulation......................................................................................................................................................................45 48 VIN Design Example........................................................................................................................................................... 56 Summary................................................................................................................................................................................. 7
7 References.............................................................................................................................................................................. 7

List of Figures
Figure 2-1. LM5013 Functional Block Diagram........................................................................................................................... 2
Figure 2-2. LM5013 Design With External Ripple Injection......................................................................................................... 3
Figure 3-1. Peak Ramp Amplitude vs VFB(AVG) ........................................................................................................................... 3
Figure 4-1. Light-load, Frequency Reduction Impact on VFB(AVG) ...............................................................................................4Figure 4-2. Light-load, Frequency Reduction Impact on VOUT Regulation.................................................................................. 4Figure 5-1. 48 V to 12 V, LM5013-Q1 Design..............................................................................................................................5Figure 5-2. Load and Line Regulation......................................................................................................................................... 6Figure 5-3. Line Transient (48 V to 15 V), Outside of Design Specification.................................................................................6Figure 5-4. Line Transient (48 V to 15 V), Zoom-in of Double Pulsing on VSW as a Result of Insufficient Ramp Injection......... 7

List of Tables
Table 3-1. Measured Peak Ramp Amplitude v. VFB(AVG) .............................................................................................................4Trademarks
All trademarks are the property of their respective owners.

SNVAA67 – MARCH 2023
Submit Document Feedback

Optimizing Line and Load Regulation in Automotive, 48-V Battery and eBike
Applications
Copyright © 2023 Texas Instruments Incorporated1Introduction

www.ti.com

1 Introduction
A common control topology employed in buck regulators is constant-on-time (COT). This control topology is
being adopted in several 48-V battery and eBike, pre-regulators such as LM5013-Q1. This application note isan overview of how line and load regulation can be optimized with LM5013-Q1 for wide-VIN range applications,specifically, the 48 V battery and eBike applications.

2 Overview of COT
Figure 2-1 produces a regulated output voltage by using its feedback comparator to servo the output bycomparing the sampled output voltage, VFB, and the reference voltage, VREF. The feedback comparator issues
an on-time pulse, after it trips. This cycle continues at the programmed switching frequency for the set output
voltage, dictated by the on-time (RRON) and feedback (RFBT, RFBB) resistors. Equation 1 and Equation 2 illustrate
the necessary calculations.
VIN

VIN

VDD

BIASREGULATORCIN

VDD UVLO
EN/UVLO–+STANDBY
THERMAL
SHUTDOWN

1.5 V–+BST

SHUTDOWN
LOGIC

0.4 V
VIN
CBST
RON

ON/OFF
TIMERSCONSTANTON-TIMECONTROL
LOGIC

VOUT
RFBT

FB
RRON

DISABLEFEEDBACKCOMPARATOR

VREF

RFBB

LO
SW

SLEEP
DETECT–+VOUT

COUT
PGOOD

PEAK CURRENT
LIMIT
FB
GND

–+PGOOD
0.9*VREF COMPARATOR

Figure 2-1. LM5013 Functional Block DiagramV
V × 2500
RRON kΩ = OUT
FSW kHzVREF
× RFBT
OUT − VREF

RFBB = V(1)(2)

The feedback comparators terminal connected to the FB node must have sufficient ripple such that during theon-time, the FB node can be charged sufficiently above the reference voltage (VREF). This outcome is achieved
with example ripple injection circuit Figure 2-2.

2

Optimizing Line and Load Regulation in Automotive, 48-V Battery and eBike
Applications
Copyright © 2023 Texas Instruments Incorporated

SNVAA67 – MARCH 2023
Submit Document Feedback

www.ti.com

Line Regulation
LO

VIN
VIN

SW
LM5013-Q1

CBSTRACIN
EN

BST

RON

FB

GND

PGOOD

VOUT

DSW

CACOUT

RFBT
CB

RRON

RFBB

Figure 2-2. LM5013 Design With External Ripple Injection
The integrator (RA, CA) generates a voltage ramp , in-phase with the inductor current and is AC coupled with CB.
By following Equation 3, Equation 4, and Equation 5 sufficient ramp amplitude is applied to the feedback node
for stability and transient performance is optimized. Note, the recommended minimum ramp amplitude, 12 mVin the case of LM5013, is advised for the device's given hysteresis, along with margin for reduced sensitivity tonoise. Please refer to the LM5013-Q1 Automotive 100-V Input, 3.5-A Non-Synchronous Buck DC/DC Converterwith Ultra-low IQ data sheet for the recommended value and further clarification of terms. Additional theory on
this design is provide in the Stability Analysis and Design of COT Type-3 Ripple Circuit application note.
CA ≥10
FSW × RFBTVRAMP =t

(3)

RFBB

VIN − VOUT × tONRACA(4)

CB ≥ 3 × TR
R

(5)

FBT

3 Line Regulation
The injected ramp waveform leads to the average feedback voltage exceeding the reference voltage for which
the output voltage was programmed with. Additionally, the waveform’s peak (Equation 4) is directly proportional
to the input voltage, leading to further variance as VIN changes. This variance is gained up through the feedback
divider, resulting in the output voltage varying from the set point. Figure 3-1 and Table 3-1 gives a conceptualand quantitative measure how higher, peak ramp amplitude results in an increase in average feedback voltage(VFB(AVG)).

VIN 1
VIN 2
VIN 1 >> VIN 2

VPEAK
VPEAK
VFB(AVG)
VFB(AVG)
VREF
Slope ∝ VIN - VOUTtSW

Figure 3-1. Peak Ramp Amplitude vs VFB(AVG)

SNVAA67 – MARCH 2023
Submit Document Feedback

Optimizing Line and Load Regulation in Automotive, 48-V Battery and eBike
Applications
Copyright © 2023 Texas Instruments Incorporated3Load Regulation

www.ti.com

Table 3-1. Measured Peak Ramp Amplitude v. VFB(AVG)
Ramp Amplitude, VPEAK (mV)

VFB(AVG) (V)

13.4881.204

15.437

1.206

20.342

1.212

23.353

1.217

23.945

1.216

4 Load Regulation
Load regulation is often a concern as well in buck regulators. Typically, regulators have a light-load mode tomake sure the light load efficiency is optimized. The implementations can differ, though, in the case of LM5013
the switching frequency decreases with reduced loading. This point is illustrated in Figure 4-1. The reduced
frequency leads to the average feedback voltage reducing. Similarly to the previous discussion, this leads tooutput variance. Figure 4-2 shows how a 12-V output decreases with reduced switching frequency.

VFB(AVG)
VREF
tSW

VFB(AVG)
VREF
tSW

Figure 4-1. Light-load, Frequency Reduction Impact on VFB(AVG)

Figure 4-2. Light-load, Frequency Reduction Impact on VOUT Regulation
This behavior can be avoided by changing the inductor so that the inductor current does not go discontinuous.
The point at which the inductor current goes discontinuous is often the entry point for light-load mode in the caseof LM5013. Alternatively, a minimum load can be applied at the output to make sure that the inductor current
does not go discontinuous. Equation 6 demonstrates the minimum inductance (LOUT) to make sure the inductor
current does not go discontinuous at the application's minimum load current (IOUT,min) with the consequence of(potential) reduced efficiency.
VOUTV× 1 − VOUTINOUT, min × FSW

LOUT ≥ 2 × I(6)

If it is not possible to manipulate either the inductance, or application's minimum load current, then an alternative
device with FPWM needs to be considered such as LMR38020-Q1 4.2-V to 80-V, 2-A Automotive Synchronous
SIMPLE SWITCHER® Power Converter with 40-µA IQ data sheet. By operating in FPWM, the device's average

4Optimizing Line and Load Regulation in Automotive, 48-V Battery and eBikeApplications
Copyright © 2023 Texas Instruments Incorporated

SNVAA67 – MARCH 2023
Submit Document Feedback

www.ti.com

48 VIN Design Example

feedback voltage will not be impacted as much by loading, as in the case of most devices who employ alight-load mode.

5 48 VIN Design Example
This application note concludes with a typical design for LM5013-Q1, a 48 V to 12 V design. The LM5013-Q1
supports a load current up to 3 A. This design often requires the input to tolerate a VIN range of 36 V to 60
V. The following calculations are presented for the ramp injection circuit selection to minimize VOUT variation.
Additionally, line and load regulation data is included, along with VOUT transient waveform in the case VIN falls
below the designed minimum VIN of 36 V, resulting in the injected ripple falling out of device specification.
1. The frequency is selected to be 300 kHz and the RRON resistor is calculated for the output voltage of 12 V.
2. The corresponding feedback resistances are calculated for for the output voltage of 12 V and selected RFBT= 453 kΩ.
3. The ramp capacitor (CA) can be calculated with the previously selected components.
4. The ramp resistor (RA) is calculated for the minimum, input voltage (largest tON), and LM5013's minimum
recommended ramp voltage of 12 mV.
5. The ramp coupling cap (CB) is determined by the arbitrarily selected transient settling time of 50 us.
6. The output capacitance of 44 μF is selected for typical load transient requirements which often supersedes
the capacitance requirements for steady state/stability. A calculation wasn't necessarily followed.
7. CIN and CBST are selected per the minimum LM5013-Q1 Automotive 100-V Input, 3.5-A Non-Synchronous
Buck DC/DC Converter with Ultra-low IQ data sheet recommendation. DSW is selected to be a Schottky
diode with a DC rating of 100 V and current rating of 3 A.
VV × 2500
2500
RRON kΩ = OUT= 12 ×= 100 kΩ
300

VREF
× RFBT = 12 1.2− 1.2 × 453 kΩ = 50.33kΩ; RFBB = 49.9 kΩ
OUT − VREF

RFBB = VCA ≥RA =(7)

FSW kHz10
FSW × RFBTRFBB=(8)10= 741pF; CA = 3.3nF
300 kHz × 44.95 kΩ

(9)36 − 12 × 100 kΩ × 10−6
VIN, MIN − VOUT × tON, MAX
36 × 2.5= 673 kΩ
=VRAMP, MIN × CA
12 mV × 3.3 nFtCB ≥ 3 × TR
R

FBT50 us= 3*453kΩ = 36 pF; CB = 56 pF

SW
LM5013-Q1CIN
2x 2.2uF

EN

RRON
100k

(11)

LO

VIN

VIN

(10)

BST

RON

FB

GND

PGOOD

VOUT

CBST

22uH

2.2nF

RA

DSW

673k
CB
56pF

CA
3.3nF

COUT

RFB1453k

2 x 22uF

RFB249.9k

Figure 5-1. 48 V to 12 V, LM5013-Q1 Design

SNVAA67 – MARCH 2023
Submit Document Feedback

Optimizing Line and Load Regulation in Automotive, 48-V Battery and eBike
Applications
Copyright © 2023 Texas Instruments Incorporated

548 VIN Design Example

www.ti.com
12.4
VIN = 36 V
VIN = 42 V
VIN = 48 V
VIN = 54 V
VIN = 60 V

12.37512.35

Output Voltage (V)12.325
12.3
12.275
12.25
12.22512.2
12.175
12.15
0

0.15

0.3

0.45

0.6

0.75

0.9

1.05

1.2

1.35 1.5 1.65
Load Current (A)

1.8

1.95

2.1

2.25

2.4

2.55

2.7

2.85

3Figure 5-2. Load and Line Regulation
The load and line regulation data above was taken at VIN = 36 V, 42 V, 48 V, 54 V, and 60 V. The load current
was varied from 0 A to 3 A.

Figure 5-3. Line Transient (48 V to 15 V), Outside of Design Specification
A line transient below the design's VIN range was applied and recorded was the VOUT transient. The converter
matained regulation after the transient, with the net effect being reduced, peak-to-peak ripple and the DC output
voltage falling. The ripple and DC output voltage fell as a result of the decreased inductor current ripple andaverage feedback voltage reducing, respectfully.

6Optimizing Line and Load Regulation in Automotive, 48-V Battery and eBike
Applications
Copyright © 2023 Texas Instruments Incorporated

SNVAA67 – MARCH 2023
Submit Document Feedback

www.ti.com

SummaryFigure 5-4. Line Transient (48 V to 15 V), Zoom-in of Double Pulsing on VSW as a Result of Insufficient
Ramp Injection
A zoom-in of the VSW and VOUT was taken to highlight the effect of insufficient ramp injection. The injected ramp
voltage falling much below 12 mV caused false triggering of PWM comparator used in the COT architecture. It
can be seen that the switching behavior becomes less periodic as a result of the double pulses on VSW (small,then large).

6 Summary
48 VIN applications larger VIN and load current range puts a bigger focus on line and load regulation for the preregulator in those designs. LM5013-Q1, a popular 48 VIN pre-regulator uses a COT topology, which by nature,
is controlled by feedback voltage variation. Increasing line and load ranges do not create worry by following thesteps outlined in this article to minimize the output variation. The concepts covered in this article need to beused in your future design to make sure best practices are being followed and the highest performance can beachieved.

7 References••Texas Instruments, Stability Analysis and Design of COT Type-3 Ripple Circuit, application note.
Texas Instruments, Selecting an Ideal Ripple Generation Network for Your COT Buck Converter, application
note.

SNVAA67 – MARCH 2023
Submit Document Feedback

Optimizing Line and Load Regulation in Automotive, 48-V Battery and eBike
Applications
Copyright © 2023 Texas Instruments Incorporated

7IMPORTANT NOTICE AND DISCLAIMER
TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATA SHEETS), DESIGN RESOURCES (INCLUDING REFERENCEDESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”
AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANYIMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRDPARTY INTELLECTUAL PROPERTY RIGHTS.
These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate
TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicablestandards, and any other safety, security, regulatory or other requirements.
These resources are subject to change without notice. TI grants you permission to use these resources only for development of anapplication that uses the TI products described in the resource. Other reproduction and display of these resources is prohibited. No license
is granted to any other TI intellectual property right or to any third party intellectual property right. TI disclaims responsibility for, and you
will fully indemnify TI and its representatives against, any claims, damages, costs, losses, and liabilities arising out of your use of theseresources.
TI’s products are provided subject to TI’s Terms of Sale or other applicable terms available either on ti.com or provided in conjunction withsuch TI products. TI’s provision of these resources does not expand or otherwise alter TI’s applicable warranties or warranty disclaimers for
TI products.
TI objects to and rejects any additional or different terms you may have proposed. IMPORTANT NOTICE
Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265
Copyright © 2023, Texas Instruments Incorporated