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Application Note
Patrick Huang
AN030 – May 2014
Wide Input Voltage LDO RT9068 for Automotive and Industrial
Applications
Abstract
Richtek Technology provides wide input voltage range linear regulator and DC/DC converter products to meet the request of
high-performance power systems for Industrial, automotive and telecommunication applications. The design challenges of these
applications due to harsh operating environments and large voltage transients are higher (12V to 42V) in automotive power
management. The telecom applications typically run from a 48V supply that may extend as higher as 72V instantaneously. For
low power operation, the supply circuits consume on a few milliamps current from high voltage input rails to keep alive. Richtek
wide input range linear regulator is an ideal solution with operating voltages of up to 60V. The wide Vin linear regulators need not
input protection components and reduce bills of materials cost and size as well as providing robustness to increase system
reliability. In the following discussion, Richtek wide Vin LDOs provide distinguishing features such robustness against input
transients, high-power density which eliminates two-stage conversions, and low noise with good PSRR performance.
Contents
Richtek Wide Input Voltage LDO Introduction ................................................................................................2
Automotive Applications ................................................................................................................................2
Multi-cells Battery Packs ...............................................................................................................................3
Motor Driver Power Tools ..............................................................................................................................4
Telecom Applications ....................................................................................................................................4
Added External NPN for High-Current Applications .......................................................................................5
LED Driver Application ..................................................................................................................................6
Summary ......................................................................................................................................................6
Reference .....................................................................................................................................................8
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Application Note
Richtek Wide Input Voltage LDO Introduction
The RT9068 is a high voltage and low dropout linear regulator in a thermally enhanced SOP-8 package. It can provide up to
50mA of output current from input supplies ranging from 4.5V to 60V. At 50mA of output current, dropout voltage on the RT9068
is only 230mV. The RT9068 operates normally on only 30μA of quiescent current. It can also be put into a low power shutdown
state by pulling the SHDN pin low, bringing quiescent current down to just 2μA. For standard operation, the SHDN pin can be
pulled as high as 60V. The RT9068 offered adjustable, fixed 2.5, 3.3 and fixed 5V output versions.
The only external components required are input and output bypass capacitors with minimum of 1μF for stability, Small ceramic
capacitors with low ESR can be used without requiring extra series resistance as is sometimes required with other regulators.
Automotive Applications
In order to manage complex electronics systems in car applications, automotive MCUs have featured one or more processors
and several of the following blocks: SRAM, flash, oscillators, PLL, AD converter, I/O (CAN, LIN, Ethernet, USB, etc.) and power
management. In automotive applications, new systems would be transitioned from 12V to 42V, but both can have transients
greater than 60V. At the same time, flexible and simple board design are paramount to reduce development costs and risks. In
automotive MCU’s an internal voltage regulator was implemented in order to supply internal IP blocks that required a stable 3.3V
supply. The limitations on power dissipation allowed the internal regulator to provide a maximum current of about 50mA. This
current would be sufficient to power flash, oscillators, and PLL. The RT9068 family maximum input voltage of 60V makes it ideal
for use in automotive applications where high-voltage transient spikes from 25V to 60V. Power connections to the RT9068 can
come directly from a battery because input transients will not damage the regulator or the load. Even when batteries are
reversely connected, RT9068 can prevent reverse current from damaging sensitive load circuits. The RT9068 family can be used
to suppress spikes with simple circuit which costs lower.
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Application Note
VIN
60V
12V
Battery
t
VOUT
VIN
VIN
MCU2
RT9068
EN
SHDN
IO2
Ignite
Signal
IO1
IO3
MCU1
Power Good Delay
Figure 1. The Microcontroller Sequencing in Automotive Applications with Load-Transients
This MCU is often an always-on circuit runs for many modern automotive subsystems. The total current consumed by all
always-on circuit must be below several milliamps. The RT9068 can also be put into the shutdown state if the sub system is not
needed.
Multi-cells Battery Packs
The battery pack with several cells connected in series may have transient voltages up to 55V in industrial application. These
battery packs has internal circuitry designed to prevent overcurrent and overvoltage conditions that may damage the
microcontroller. Meanwhile, the microcontroller continuously monitors the battery itself and may degrade battery life. The best
approach to power this microcontroller is to regulate down the voltage from the multi-cells battery; RT9068 is the ideal regulator
for this application for very high voltages supply and very low quiescent current to maximize battery life.
Sensing
……
……
Up to 42V
+
Cell
Balance
RT9068
Comparator
Voltage
Sensing
MCU
UART
-
Figure 2. The Multi-cells Battery Packs with MCU application
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Application Note
Motor Driver Power Tools
In high-power applications for motor, a MCU controls the motor powered by batteries. This MCU must be powered with a
low-voltage rail coming from the high-voltage in multi-cell battery pack. In addition, this MCU must be protected from the
high-voltage transients because of the motor inductance. The RT9068 is an ideal solution for powering the motor-controlled MCU
with low quiescent current and very high-voltage capabilities with low system cost.
Transient
100 
…
0.47μF
Optional
Filter
RT9068
M
MCU
PWM
Figure 3. The Motor Power Tool with MCU application
Telecom Applications
In telecom application where 48V rail powers a keep-alive circuit for monitoring, the quiescent current specification is important,
especially when battery back-up kicks in to keep the output alive when a fault occurs on the input. The 48V input rail in telecom
applications can have transient voltages as high as 72V. In Industrial applications, the long wire with high voltage power line
would cause the transient voltage spikes spans even wider and reverse input (-60V to 0V) from output are also possible.
The RT9068 provides an optimum solution for such harsh conditions when reverse voltage from output to input, RT9068 prevents
current flow from the output back to the input, removing the need for protection diodes.
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Application Note
No Protection Diode
72V
Short pulse < 1msec
Spike<100mV
48V or 60V
VOUT
VIN
Output
Input
RT9068
SHDN
SENSE/FB
No TVS
Figure 4. Typical telecom application for the RT9068
Added External NPN for High-Current Applications
Higher output currents and/or increased power dissipation are possible using an external NPN output transistor in
adjustable-output version RT9068GFP. VOUT drives the base of the transistor and SENSE and/or FB monitors the actual output
voltage as shown in Figure 5.
VIN
4.5V to 60V
MJD31C
VOUT
VIN
CIN
0.18µF
100
VOUT
1.25V to 60V
CCOMP
SENSE
R1
SHDN
COUT
10µF
FB
R2
GND
Figure 5. High driving output current application for the RT9068
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Application Note
LED Driver Application
The RT9068 can be used to drive several LEDs connected in series, as shown in Figure 6. By control the PWM dimming signal at
its SHDN pin, the array of serial LED could have the intensity dimming behavior. It is a simplified version with low-cost for higher
input voltage LED driver implemented by RT9068.
Figure 6. LED Array Driver Application of RT9068
Summary
The RT9068 offers exceptional performance in a small package. It can supply low voltage from high voltage rails in applications
that previously required external pre-regulation schemes or complex switching supplies. Low quiescent current minimizes the
power consumption and can be dropped even further by placing the part into shutdown state. Stable output voltage is available
with a wide range of output capacitors including small ceramics. Internal protection circuitry in the RT9068 eliminates the need for
external protection diodes. The thermally enhanced 8-lead MSOP package provides low thermal resistance and is suitable for
using in harsh environments.
In many applications including communications, automotive, and industrial systems, wide input voltages as high as 60V to 80V
will convert to 24V/12V/5V or lower to supply electronic systems. In many 12V and 24V systems, transient approaches 80V are
commonly occurred and need to be carefully considered.
RT9068 provides the industry’s most comprehensive wide input voltage range to 60V and eliminates input protection
components to reduce cost and solution size while increases system reliability. Additionally, a single device can operate across
several voltage rails to provide scalability and allow reuse of power converter designs.
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Application Note
Type
Status
HV Low IQ
RT9058
RT9069
RT9068
RT2501
RT2064Q
RT2572
Released
Released
Released
Upcoming
Upcoming
Upcoming
Operational
VIN (V)
AMR (V)
VOUT (V)
Ultra High Voltage
3.5V ~ 36V
4.5V ~ 60V
4.5V ~ 80V
-0.3V ~ 40V
-60V ~ 80V
-80V ~ 90V
2.5V/3V/3.3V/5V/
2.5V/3V/3.3V/5V/
6V/9V/12V
6V/9V/12V
2.5V/3.3V/5V
2.5V/3.3V/5V
2.5V/3.3V/5V
1.25V ~ 60V
1.25V ~ 60V
1.25V ~ 60V
Adjustable
Adjustable
Adjustable
ADJ
IOUT (mA)
100mA
200mA
50mA
250mA
100mA
20mA
ILIM (mA)
115mA
200mA
120mA
450mA
200mA
40mA
IQ (μA)
2μA
2μA
30μA
50μA
30μA
23μA
ISHDN (μA)
0.5μA
0.5μA
2μA
3μA
2μA
3μA
Accuracy (%)
±2
±2
±2
±2
±2
±2
SOT-23-3
SOT-23-5
PSOP-8
PSOP-8
PSOP-8
SOT-23-5
SOT-23-3 (L)
SOT-89-5
MSOP-8
TO-252
MSOP-8
DFN3x3-8
SOT-89-3
PSOP-8
SOT-223
Package
SOT-223
PSOP-8
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Application Note
Reference
[1] Stefano Pietri,Chris Dao, Jehoda Refaeli, Alfredo Olmos, and Xiaolei Wu, “A Versatile
Low-Dropout Voltage Regulator for Automotive Applications”, IEEE 2011.
[2] Ashok Bindra, “Selecting the Right Ultra-Low Quiescent-Current LDO Regulator “,
Digi-Key Corporation Article Library, 2014.
Related Parts
RT9058
36V, 2μA IQ, 100mA Low Dropout Voltage Linear Regulator
Datasheet
RT9069
36V, 2μA IQ, 200mA Low Dropout Voltage Linear Regulator
Datasheet
RT9068
60V, 30μA IQ, Low Dropout Voltage Linear Regulator
Datasheet
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Richtek Technology Corporation
st
14F, No. 8, Tai Yuen 1 Street, Chupei City
Hsinchu, Taiwan, R.O.C.
Tel: 886-3-5526789
Richtek products are sold by description only. Richtek reserves the right to change the circuitry and/or specifications without notice at any time. Customers should
obtain the latest relevant information and data sheets before placing orders and should verify that such information is current and complete. Richtek cannot assume
responsibility for use of any circuitry other than circuitry entirely embodied in a Richtek product. Information furnished by Richtek is believed to be accurate and
reliable. However, no responsibility is assumed by Richtek or its subsidiaries for its use; nor for any infringements of patents or other rights of third parties which may
result from its use. No license is granted by implication or otherwise under any patent or patent rights of Richtek or its subsidiaries.
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