CMOS LDO Regulators

Innovations Embedded
CMOS LDO Regulators
for portable devices
White Paper
ROHM MarketingUSA
Presented by ROHM Semiconductor
CMOS LDO Regulators
for Portable Devices
Introduction
Power management has become an increasingly
LDOs provide a power management solution satisfying
important design consideration for numerous products,
the need for low power, space-conscious design and
especially those relying on battery power. Complicating
low switching-noise voltage regulation while adhering to
the power management situation, as more features get
the cost constraints of these applications.
integrated into products, the number of required voltage
Other LDO applications include PC motherboards,
supplies increases. With a common 3.6-V lithium-ion
graphic cards, post-regulation in switching power sup-
battery, a highly integrated product such as a smart
plies, telecom equipment and consumer applications
phone can require ten or more different voltages for:
such as HDTVs. In addition, automotive applications
1. Global positioning system (GPS)
continue to use LDOs for their low switching noise and
2. Power amplifier
low cost.
3. Memory
According to Susie Inouye, Research Director and
4. Baseband and DSP core
Principal Analyst at market research firm Databeans,
5. Applications (picture, music and video)
processing
“LDOs are still the best fit for low current applications.
6. Low voltage wireless LAN
complex switching regulators. Noise performance in
7. Display back light LED drivers
portable electronics is an important design consider-
They are inexpensive and have lower noise than more
ation, particularly in wireless as high frequency parts can
8. Display CCD
impact performance of sensitive analog RF circuits. As
9. Audio
long as price, size, and noise performance matter, there
10. Photo flash charger
will be a growing market for LDOs.”
To handle all of these voltages, cell phones typically
Databeans forecasts a compound average growth rate
have power management ICs with multiple LDOs.
(CAGR) of 15% unit growth for LDOs from 2009 to
However, depending on the location of the load, an
2014. Advances in the latest CMOS LDOs are among
individual LDO may be used.
the reasons for this growth.
While switching regulators garner a lot of attention
This paper reviews the basics of LDO regulators and
because of their high efficiency, low drop-out (LDO)
discusses the technology advances in the latest genera-
linear voltage regulators offer the optimum answer for
tion of LDOs that make them the preferred solution for
powering circuitry in many of the portable device appli-
many point of load power requirements. The paper will
cations. The latest generation of LDOs is optimized for
also introduce ROHM Semiconductor’s extensive line of
cell phones, PDAs, MP3 players, notebooks, cameras,
CMOS LDO regulators and discuss their unique benefits
camcorders and other handheld portable systems.
in portable electronics applications.
ROHM Semiconductor
LDO Regulators
1
Pass Element
Q1
VIN
VOUT
Error Amplification
VREF
_
OUT
Bandgap
Reference
R1
+
VC
R2
Figure 1. The pass element, Q1, in a low drop out regulator operates in the linear range and can be a bipolar
NPN or PNP transistor, a Darlington pair, or an N-channel or P-channel MOSFET.
The Basic LDO Topology
operating current. (For example, ROHM’s recently intro-
Low drop-out linear regulators are designed to operate
with minimal voltage differences between the source
voltage (VIN ) and the regulated output voltage (VOUT ).
This value, known as the saturation voltage (VSAT ) is
duced PB1 series requires just 20 μA under high-speed
operation and only 2 μA when in its unique power-save
mode.) The resulting LDO design provides optimized
performance for portable applications.
typically in the 100 mV to 200 mV range. This allows for
effective regulation of load voltages as battery voltage
Comparison of LDOs to PWM Regulators
diminishes as the battery discharges.
For the majority of applications within portable devices
The basic LDO topology is shown in Figure 1. Using
where loads are operated from a battery source, the
a resistor divider, a voltage-controlled current source
LDO offers a simple, small and cost-effective solution.
determines the output voltage. Key elements include
While it is true that switching regulators are more effi-
the voltage reference, an error amplifier and the series
cient than LDOs, there are several other factors that
pass transistor. Input and output capacitors are typi-
must be considered in selecting the right device for the
cally among the few external components required for
job.
proper LDO operation.
Pulse-width modulated (PWM) switching regulators typ-
Advanced LDOs utilize BiCMOS process technology
ically operate between 50 kHz to 1 MHz and produce
to provide higher efficiency, additional application-
electromagnetic interference (EMI) that can disrupt both
specific features and space-saving packaging. With
analog and RF circuits. In contrast, the switching in
BiCMOS, a merged bipolar and CMOS wafer fabrica-
LDOs occurs in the bandgap reference and the level is
tion process, an LDO designer can take advantage
in the microvolt, rms range over a defined bandwidth, a
of circuit elements of each technology. For example,
level that is considerably lower than a switching regula-
the bandgap reference is an ideal bipolar circuit ele-
tor. This is a major design advantage in noise-sensitive
ment while the output pass transistor can be a highly
applications.
efficient P-channel MOSFET that results in very low
ROHM Semiconductor
LDO Regulators
2
Additional advantages of fewer external components,
Regulator Type
Linear (LDO)
Switching
simple design process, small footprint, and lower cost
External Components
advantage
---
make LDOs a preferred solution for regulated power
Noise sensitivity
advantage
---
Design Complexity
simple
complex
Cost
advantage
---
lower than the source voltage. Moreover, the latest
Footprint
advantage
---
advances in CMOS LDOs, such as BiCMOS devices
Step-down (buck voltage)
yes
yes
Step-up (boost voltage)
no
yes
Efficiency
---
advantage
Thermal design
---
advantage
in many applications where the controlled voltage is
with a P-channel output transistor and power down
capabilities as found in ROHM CMOS LDO regulators,
significantly reduce the efficiency advantage of PWM
Table 1. Compared to switching regulators, LDOs have several
design areas where their advantages make them a
compelling choice.
regulators – particularly in low-current applications.
Table 1 summarizes the significant points of compari-
to consider the level of electrostatic discharge (ESD)
son between LDO and switching regulators.
withstand capability. Finally, package size must be
taken into consideration in selecting the right device for
Selecting the Right LDO for the Job
space-conscious portable devices.
An LDO’s drop out voltage, the type and range of input
Figure 2 illustrates several features that can be added
voltage, required output voltage, maximum load current
to an LDO to satisfy application requirements in the lat-
and power dissipation (Pd) are key factors in product
est portable and wireless products. This paper will dis-
selection. In portable applications, it is also important
cuss the importance of many of these features.
High ripple rejection
Stable Operation
Reduced input/output
voltage difference
VIN
VREF
VOUT
STBY
0μA standby
current
COUT
TSD
APS
OCP
Temperature
protection
High output
precision
Overcurrent
protection
Automatic
Power Saving
Ceramic capacitor
compatibility
Discharge circuit for
secure startup
Figure 2. Additional circuitry and advanced packaging can make an LDO the ideal choice for a particular application.
ROHM CMOS LDO regulators are available in several series offering many of these advanced features.
ROHM Semiconductor
LDO Regulators
3
 Package Size and Power Dissipation
 Automatic Power Saving Function
Packaging has a significant impact on PCB space and
With CMOS processing, advanced features such as
power dissipation. For example, an HVSOF5 (1.6 x 1.6
an Automatic Power Saving (APS) function can be
2
mm ) packaged LDO is over 70% smaller than a 2.8 x
designed to further increase the efficiency of an LDO.
2.9-mm2 SOT23-5, achieving the same current rating
With APS, the circuit varies the current consumption
while improving the effective power dissipation (Pd).
based on the value of the load. This can result in as
much as 90% less current during no load conditions.
ROHM
ROHM
ROHM
ROHM
VCSP60N1
SSON004X1216
HVSOF5
HVSOF6
1.0
1.2
1.04
1.6
1.2
1.6
1.6
1.6
1.6
1.6
1.6
1.6
3.0
3.0
0.6
540 mW
220 mW
410 mW
680 mW
87% smaller
76% smaller
70% smaller
40% smaller
76% smaller
54% smaller
39% smaller
NA
2.8
Conventional
SOT23-5
2.9
540 mW
2.1
Conventional
SC82
2.0
400 mW
Figure 3. A small LDO package provides a substantial space savings for portable applications and with the right substrate
design, can dissipate 100s of milliwatts.
Figure 3 shows the size reduction of four ROHM LDO
 High-Speed Load Response
packages and nominal power disipation compared to
the industry-standard SOT23-5 (ROHM SSOP5) and
CMOS LDOs are ideal for powering microcontrollers,
digital signal processors, microprocessors, memory
SC82 packages.
and other digital logic circuits. A critical feature in this
In many packages, an integrated heatsink increases the
application is high-speed load response. If the regulator
heat transfer allowing the package to safely dissipate
does not respond quickly enough, its output has the
more heat. The ability to dissipate more heat is espe-
potential to fall below the minimum voltage differential
cially useful in high-density portable devices. The safe
required for reliable operation. A low VSAT allows stable
power dissipation for a particular package also depends
on the ambient temperature and mounting substrate.
operation even when the battery is close to being fully
discharged.
Package ratings (e.g. SSOP5: 540 mW; HVSOF6: 680
mW; HVSOF5: 410 mW; SSON004X1216: 220 mW;
and VCSP60N1: 540 mW; VSON008X2030: 660 mW)
are for power dissipation at 25°C operation. The value
of Pd normally decreases with increasing ambient temperature. In addition, the power dissipation will differ
depending on the mounting conditions and substrate
(board type, size and copper foil area).
ROHM Semiconductor
Figure 4 demonstrates the importance of fast load
response. A “conventional” LDO exhibits nearly 100
mV drop in VOUT, compared to the ROHM BUxxTA2
Series LDO optimized for high-speed load response.
This added margin can reduce the potential for “dropout” and extend operation as the battery voltage
approaches discharge.
LDO Regulators
4
100mA (Cout = 1.0μF)
Iout = 0mA
OUtput voltage (V)
50
0
3.020
3.000
2.980
2.960
100mA (Cout = 1.0μF)
100
50
OUtput voltage (V)
100
Output current (mA)
Iout = 0mA
ROHM TA2 Series
0
3.020
3.000
Output current (mA)
Conventional
2.980
2.960
High-speed response
ΔV =
mV
ΔV = 98mV
20
Figure 4. A high-speed load response LDO assures that the output voltage regulation can be sustained, even as the battery
voltage falls as the battery is close be being fully discharged.
 Ripple Rejection and Circuit Footprint
Ripple Rejection Characteristics
LDOs are also used to power RF and analog circuitry
100
in portable consumer products. LDOs optimized for
90
Ripple Rejection (dB)
high ripple rejection insure a clean output for powering
these circuits. (See Figure 5.) Devices equipped with
internal phase compensation provide higher levels of
ripple rejection, often without the need for external filter
capacitors, resulting in a simpler solution and smaller
80
70
ROHM
60
50
Conventional
40
circuit footprint.
30
 Reverse Current Protection and Circuit Footprint
20
100
1K
If VIN is lower than VOUT when the LDO is turned off,
(due to a residual charge on the output capacitor, for
example) a damaging reverse current could flow from
the output to the input. A standard feature of all ROHM
10K
100K
Frequency (Hz)
Figure 5. Internal phase compensation significantly enhances ripple
rejection without the need for external filter capacitors.
Some ROHM LDOs attain rejection ratios of 70 dB and higher
as shown by blue traces as compared to typical devices.
CMOS LDOs is an internal circuit, as shown in Figure
6, which safely discharges the output capacitor without
the need for external blocking diodes and further reduc-
D2
es the overall circuit footprint.
D1
 Overtemperature and Overcurrent Protection and
VIN
Thermal Design
VOUT
Built-in foldback type overcurrent protection prevents
STBY
damage and can reduce the heating effects of current
overload conditions on the LDO and surrounding cir-
Discharge function
cuitry. Thermal protection further restricts the device’s
temperature. These protection circuits combine to limit
total heating during operation and can simplify thermal
Figure 6. An internal discharge circuit prevents reverse current
flow and eliminates the need for diodes D1 and D2.
design.
ROHM Semiconductor
LDO Regulators
5
ROHM Semiconductor LDO Solutions
ROHM Semiconductor CMOS LDOs for portable devices provide designers several advantages including:
• High-accuracy output voltage ±1% over a wide
temperature range
• Compatible with compact ceramic capacitors for
an overall smaller footprint
• Low current consumption (as low as 20 μA with
the BHxxPB1 series in high-speed mode)
Standard CMOS LDOs [LB1 and FB1 series] from
ROHM Semiconductor have a low (40 μA) current consumption and high (70 dB) ripple rejection in a small
(1.6 x 1.6 mm2) HVSOF5 package. (Also offered in the
industry-standard SOT25-5 package.) The low current
consumption provides extended battery life in portable
applications.High ripple rejection assures a stable output for improved performance. These products provide
a good starting point for many portable products, such
as camcorders, notebook computers and MP3 players.
• 0 μA standby current
For tighter design criteria, other families extend these
• Built-in foldback type overcurrent protection
(See Figure 7)
capabilities and add functionality for higher performance.
• Built-in thermal shutdown
• Built-in discharge circuit to prevent malfunction
when entering standby mode or at power-on
Automatic Power Saving Function LDOs [PB1
series] continuously monitor the output current and
automatically select either the low current consump-
• High ESD protection
tion or the high-speed operation circuit depending on
• Soft-start [BH6733]
real time conditions as shown in Figure 8. This unique
• Automatic Power Saving (APS) function to reduce
power consumption during light-load conditions
[BHxxPB1 series]
• High (300 mA) output current [BHxxMA3 series]
approach reduces operating current to just 2 μA under
light-load conditions. Another design feature is the
output discharge function that reduces the time duration of 0 V during start up from 1 second to 10 ms for
• High ripple rejection of 70 dB or even 80 dB
[BHxxNB1 series]
improved stability. Inrush current protection, overcurrent protection, thermal shutdown, 1.7V operation, 1%
• High-speed load response
voltage accuracy and 8kV ESD protection are among
• Ultra-compact molded package [BHxxTA2 series]
or chip scale package [BHxxRB1 series]
the added features in this product family for increased
durability and performance. This family provides an
These performance advantages are implemented in a
excellent solution for extending the battery life in cell
variety of product families (indicated above in brackets).
phones and other handheld portable products.
ROHM Foldback Type
3.5
3
3
Output voltage (V)
Output voltage (V)
Conventional Droop Type
3.5
2.5
2
1.5
1
Large short-circuit
currents result in excessive
heat generation
0.5
0
2.5
2
Safe against
small short-circuit
currents
1.5
1
0.5
100
200
300
400
0
100
Load current (mA)
200
300
400
Load current (mA)
Figure 7. Foldback overcurrent protection reduces device heating during fault conditions.
ROHM Semiconductor
LDO Regulators
6
Measurement Conditions
BH12PB1WHFV
VCC = 2.2V
VSEL = open,
VSTBY = 1.5V
Vcc
Low Power
Consumption LDO
SW
(During Standby)
Fast Load
Response LDO
(During Normal
Operation)
VOUT
Current
monitor
GND current IGND (μA)
Automatic switching
30
High-speed response mode
20
10
Low consumption mode
0
0
0.5
1
1.5
2
2.5
3
Output current IOUT (mA)
Hybrid system
Figure 8. The automatic switching between low power consumption and fast load response modes in ROHM Semiconductor’s
proprietary Automatic Power Saving (APS) function provides a power savings without compromising performance.
High current [MA3 series] LDOs include a proprietary
ROHM
feedback circuit, low ON-resistance, and two parallel
100mA (Cout = 1.0μF)
output terminals (see Figure 9) to enable stable load
100
50
OUtput voltage (V)
regulation as low as 6 mV compared to conventional
regulators at 30 mV. The compact (1.6 x 3.0 mm2) high
power (Pd = 680 mW) HVSOF6 package has an underside heatsink for high thermal dissipation. In addition to
0
3.020
3.000
OUtput current mA)
Iout = 0mA
2.980
2.960
higher power loads in battery-powered products, this
High-speed response
ΔV =
mV
20
higher current LDO can handle loads in graphics cards,
Iout = 0mA
100mA (Cout = 1.0μF)
HDTVs.
100
Output voltage (V)
50
Only
6mV
0.6Ω
low ON
resistance
FET
Output voltage (V)
Dual output
terminal
3.0
ROHM
30mV
100
200
3.000
2.980
2.960
ΔV = 98mV
Conventional
0
0
3.020
OUtput current (mA)
Conventional
telecom equipment and consumer applications such as
300
Load current (mA)
Figure 9. ROHM’s MA3 series LDOs exhibit a voltage drop of just
6 mV (IOut = 100 mA) instead of 30 mV in comparable
devices.
Figure 10. High-speed load regulation reduces load response from
nearly 100 MV to only 20 MV with an output step-change
from 0 to 100 mA.
SSON004X1216 (1.6 x 1.2 x 0.6 mm3) package, TA2
series devices are 25% smaller than the HSVOF5.
Ideal for high-speed processing and data reading in
High speed load response [TA2 series] LDOs
high-density logic and memory applications, these
reduce the fast load response to just 20 mV while
transitoning from 0 to 100 mA output current compared to conventional regulator values of up to 98 mV
as shown in Figure 10. Offered in the ultra compact
ROHM Semiconductor
LDOs are frequently used in portable audio circuits and
in digital cameras as well as portable computers, PC
mother boards and graphic cards.
LDO Regulators
7
a
b
CSP Construction
SOT23-5
(SSOP5)
VCSP60N1
2.8
Power dissipation
540mW
Ultra-thin
Cu POST construction
compatible with PCBs
No cracking
during
installation
1.0
(when mounted on a substrate)
Mounting area
1.04
1
8
0.6
Overcoat
2.9
POST
structure
Silicon
0.6 mm
Thickness
1.25
4X magnification
Actual size
PCB
[Unit : mm]
Small solder balls can be
attached to prevent problems
during installation
Figure 11. LDO products in the Chip Scale Package (CSP) (a) occupy 1/8 the mounting area of a SOT23-5 package and (b)
utilize sophisticated packaging techniques to avoid reliability problems during assembly.
High ripple rejection [NB1 series] provide an addi-
tions under the most severe space constraints such as
tional 10 dB of margin for a total 80 dB at 1 KHz and
smart cell phones and digital cameras.
improved ripple rejection over a broader frequency
The three-channel output, BU665xNUX Series
range. These units also have 6 mV load regulation
combines a number of the advantages of the single-
and 1 mV line regulation ensuring stable power supply
channel ROHM CMOS LDOs while providing three
operation even in applications with significantly varying
independent outputs in a single, compact device that
load currents. In addition, proprietary phase compensa-
reduces mounting costs and board wiring. Three com-
tion circuitry in the design may eliminate the need for an
binations of output voltages are offered, each with 200
external capacitor providing space reduction and lower
mA per channel output current (Pd = 660W, max.), low
system cost. This family provides improved line and
current consumption and ON/OFF control for each
load regulation for analog applications in portable prod-
channel as well as 1% output voltage tolerance, over-
ucts such as sensor and audio applications common in
current protection and thermal shutdown.
cell phones, camcorders and digital cameras.
The Chip Scale Package (CSP) [RB1 series] pro-
Conclusion
vides an even smaller footprint than ultra-small molded
As battery powered, wireless products proliferate,
packages. The 4-pin CSP shown in Figure 11(a) mea-
system designers can continue to count on LDOs for
3
suring 1.04 x 1.0 x 0.6 mm , just slightly larger than the
regulated power sources with low noise and space sav-
chip itself, has a mounting area that occupies only /8
ing design. Specifically designed for low power appli-
of the PCB space of a standard 2.8 x 2.9 x1.25-mm3
cations in portable products, ROHM Semiconductor
SOT23-5. Increased performance capabilities come
CMOS LDOs provide a variety of solutions for efficient
from the RB1 series’ low input/output voltage difference
and cost-effective power management. Package size,
of 100 mV @ Io=100 mA, and current consumption as
power efficiency, dynamic regulation and ripple rejec-
low as 34 μA making it highly desirable in lower input
tion are among the features that should be considered
voltage applications. As shown in Figure 11(b), CSP
in making an LDO selection. ROHM Semiconductor’s
technology includes design considerations that improve
complete line of CMOS LDOs combined with expert
reliability and minimize end product manufacturing
application engineering support assures the optimum
problems. The RB1 series is ideal for portable applica-
choice for every application.
1
ROHM Semiconductor
LDO Regulators
8
10145 Pacific Heights Blvd., Suite 1000
San Diego, CA 92121
www.rohmsemiconductor.com | 1.888.775.ROHM
NOTE: For the most current product information, contact a ROHM sales representative in your area.
ROHM assumes no responsibility for the use of any circuits described herein, conveys no license under any patent or other right, and
makes no representations that the circuits are free from patent infringement. Specifications subject to change without notice for the purpose
of improvement.
The products listed in this catalog are designed to be used with ordinary electronic equipment or devices (such as audio visual equipment,
office-automation equipment, communications devices, electrical appliances and electronic toys). Should you intend to use these products
with equipment or devices which require an extremely high level of reliability and the malfunction of which would directly endanger human
life (such as medical instruments, transportation equipment, aerospace machinery, nuclear-reactor controllers, fuel controllers and other
safety devices), please be sure to consult with our sales representative in advance.
© 2009 ROHM Semiconductor USA, LLC. Although every effort has been made to ensure accuracy, ROHM accepts no responsibility for
errors or omissions. Specifications and product availability may be revised without notice. No part of this document represents an offer or
contract. Industry part numbers, where specified, are given as an approximate comparative guide to circuit function only. Consult ROHM
prior to use of components in safety, health or life-critical systems. All trademarks acknowledged.
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