Download Car Audio System Power Supply IC Lowers Power Use A s the use

Car Audio System Power Supply IC Lowers Power Use
As the use of electronics in automobiles increases steadily in recent years, there is a higher level of demand
for improving the fuel efficiency. Wide ranging development efforts, such as reducing the car body weight
as well as improving tire performance and efficiency of electronic circuits are being made by automobile
manufacturers as a main driving force. On the other hand, in the car infotainment equipment sector such as
the car audio field, new functions, like Universal Serial Bus (USB) and Bluetooth compatibility added in
products have led to an increase in the number of power supply channels and current consumption. Such
high power consumption directly affect the fuel
efficiency of electric vehicles (EV) and hybrid vehicles
(HV) as well as the fuel efficiency of gasoline engine
automobiles because the power generator is used and the
engine load increases. For that reason, there has been
strong demand for improving efficiency in order to
achieve lower power consumption.
In this article, ROHM Co., Ltd. introduces a nextgeneration car audio system power supply IC called
BD49101AEFS-M that uses a high-efficiency switching
regulator to reduce the operating power by 65 percent
compared
with
conventional
operating
power
(comparison with the company’s own products)
(Fig. 1).
BD49101AEFS-M has the following features: 1) maximum rated voltage of 42V; 2) operating voltage
range of 5.5 to 25V; 3) 2-channel high-withstand voltage switching regulator; 4) 2-channel high-withstand
voltage series regulator; 5) 3-channel low-withstand voltage series regulator; 6) high-withstand voltage Hi
Side switch one channel.
BD49101AEFS-M is a system power supply IC that is equipped with a battery power supply detection
circuit, serial interface, and various protection functions, and it integrates all the power supplies required for
car audio on a single chip by adopting a HTSSOP-A44 surface-mount package. In addition to reducing the
operating power of car audio systems, it also has been possible to reduce the weight of a conventionally
required heat sink, which in turn contributes to improving fuel consumption in vehicles.
Configurations of Car Audio Power Supply IC
This section describes the configurations of power supply ICs used in car audio systems. There are two
types of power supply configurations depending on the applications. One is a configuration that combines
discrete ICs, and the other is a system power supply that integrates multiple power supplies in a single chip.
The former type of configuration offers users a wider range in the choice of components and design
flexibility, but the number of components to be used increases, and the On/Off control of each IC must be
performed independently. On the other hand, the latter type of configuration offers advantages such as a
significant reduction in the number of components to be used as the required power supplies as well as
functions including the battery voltage detection function are assembled on a single IC; reduction in the
design workload of users; and simultaneous On/Off control of all power supplies.
Power Supply Circuit Methods
This section describes power circuit methods. Power circuit methods can be roughly classified into two
types. One is the linear type called series regulators, droppers, or low dropout regulators (LDO). The other is
the switching type called switching regulators or DC/DC converters. Series regulators have advantages such
as requiring less external components, low cost, and being comparatively simple to use. The downsides of
series regulators are poor power efficiency and high heat generation. Car audio power supply ICs use the
12V car battery for their power supply and from this battery the ICs supply power to internal devices. With
the advances made in miniaturization of devices in recent years, there is an increase in the use of car
batteries with an operating voltage of 5V or less and an increase in current consumption due to
implementation of higher functionality. For example, when the input voltage, output voltage, and current
consumption of a series regulator are 12V, 3.3V, and 0.3A, respectively, its power consumption will be: (12
– 3.3) × 0.3 = 2.61W. The power efficiency of this example is 27.5 percent and more than 70 percent is
consumed as heat.
On the other hand, there are downsides to switching regulators such as an increase in the number of
external components, larger circuit scale, higher cost, and more complicated design. Under the same
conditions as mentioned above, however, power efficiency of switching regulators can be improved by more
than 85 percent and heat generation can be suppressed to a considerable extent.
Conventional vis-à-vis New System Power Supply IC
As conventional car audio system power supply
ICs are configured with series regulators, they have
high heat generation and most of them require heat
sinks. For that reason, insertion type large-size
packages such as Single Inline Package (SIP) or
Zigzag Inline Package (ZIP) are used.
The number of power supply channels that can be
assembled in conventional system power supply ICs
is also limited, and therefore it is often necessary to
add an additional power supply IC in order to cope
with the multi-functionality of car audio systems.
When the series regulator is replaced with a highefficiency switching regulator, heat generation can
be significantly reduced, but this results in
disadvantages such as an increase in the number of
external components and higher cost of the IC.
To resolve the above disadvantages, BD49101AEFS-M has adopted a hybrid configuration in which the
battery voltage is temporarily stepped down by the switching regulator and some of the series regulators are
placed under the above switching regulator (Fig. 2).
BD49101AEFS-M is optimized
with a combination of two
switching regulators and five
series regulators and as a result it
achieves both a significant
improvement of power efficiency
and reduction of cost.
The improved power efficiency
drastically
suppresses
heat
generation.
BD49101AEFS-M
enables the use of a surface-mount
package instead of a conventional insertion type package and allows an approximately 1 to 14th size
reduction (compared with ROHM’s own products) (Fig. 3).
Low Power Consumption Technology
The power efficiency of switching regulators is high, but the efficiency drops when the load current is
small.
Some of the circuits such as microcontrollers (MCU) of car audio systems operate in standby state and
therefore require power to be supplied even when the car audio power is turned Off while the car is parked, for
example. In such a state, the current consumption of MCUs drops to less than 1mA. This drop in current
consumption occurs when the operating current of the circuit itself is higher than the load current of the
switching regulator, and power efficiency drops to less than 7 percent, which is even lower than the efficiency
of series regulators (Fig. 4).
There is an efficiency-enhancing technique for the
light load state where the operation is performed
using pulse-width modulation (PWM) control during
a high load state and switched to pulse-frequency
modulation (PFM) control during a light load state.
This technique decreases the switching frequency
during a light load state and reduces the switching
loss. When this technique is used, however, noise
suppression becomes difficult because the switching
frequency changes and it is also difficult to provide
higher power efficiency than series regulators when
the load current is very small, such as less than 1mA.
For that reason, BD49101AEFS-M has adopted the
method of switching between switching regulators
and standby series regulators for the MCU power
supply, which is required to operate at all times. In
this way, BD49101AEFS-M achieves both high
power efficiency and low current consumption during
standby state.
There is, however, the issue of voltage fluctuation
when the regulators are switched in this method.
When BD49101AEFS-M enters normal operation
from standby state, the MCUs start operating and the
load current increases significantly. At this time, if the
power supply is simply switched from the series
regulators to switching regulators, the output voltage
may drop sharply. If the voltage drop is large, the
MCUs are reset in some cases. Although the condition can be improved by mounting a large-capacitance
capacitor, it will lead to other issues such as additional
component costs and a bigger footprint.
This section describes the operation principle of
switching regulators.
Switching regulators are configured with an error
amplifier for comparing the output voltage with the
reference voltage, a PWM comparator for comparing the
above output with ramp waves, an output transistor that is
operated using pulses generated by the comparator, and
an LC filter for smoothing the above current output.
Switching regulators maintain the voltage by performing
feedback operations that keep the pulse width constant
(Fig. 5).
When the regulators are switched, the voltage drops because the abovementioned series of feedback
operations cannot be performed immediately after the switching occurs. To improve this condition,
BD49101AEFS-M applies the following three controls: (1) Operates both regulators for a specific period of
time while the regulators are switched: (2) The error amplifier output is pre-charged to a specific voltage so
that the PWM comparator can immediately output the specified pulse width during the period of item (1)
above; (3) The series regulators are turned Off and operation is performed using switching regulators only.
Because of the above controls, the feedback loop enters into a stable operation within a short period of
time, and this makes it possible to suppress voltage drop. Thus, it has been possible to suppress the output
voltage drop of BD49101AEFS-M to less than 40mV compared with a more than 300mV drop when the
power supply is simply switched from series regulators to switching regulators (Fig. 6).
As a result of adopting this
method, the BD49101AEFS-M IC
achieves a current consumption of
100A (typ.) during standby state
and enables reduction of the dark
current produced by the car audio
while the automobile engine is
turned Off.
Further Enhanced Functionalities
BD49101AEFS-M is equipped with a cable impedance voltage compensation function for the USB power
supply in order to cope with the incorporation of higher functionalities for car audio systems (Fig. 5). This
function has been provided in order to meet the requirements of USB standards by increasing the output
voltage for the amount of voltage dropped by the power supply IC side and maintaining a stable voltage at
the end of the cable. This compensation amount can be adjusted in accordance with the cable to be used by
setting the amount using an external resistor. This IC is provided with the dedicated terminal for stopping
the output and sending an overcurrent notification to MCUs when overcurrent is detected.
Furthermore, the battery power supply detection circuit of this IC can be set in 0.1V steps and provides a
detection voltage range between 5.7V and 6.4V in addition to one between 7.7V and 8.4V so that this IC can
detect the battery power supply for low-voltage operation of the unit.
Conclusion
ROHM has been positively working on increasing efforts on environmentally friendly product
development. The power to be reduced by this newly developed BD49101AEFS-M IC is not significant
from the standpoint of the entire vehicle power consumption. Nonetheless, the company intends to enhance
the lineup of these products in order to contribute to social needs.
About The Article:
ROHM Co., Ltd. provided the contents of the article.