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Datasheet
Ground Isolation Amplifier
BA3121F
General Description
Key Specifications
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BA3121F is a ground isolation amplifier developed for
car audio applications. This IC efficiently eliminates
problems caused by wiring resistance and removes
noise generated by other electrical devices used in
automobiles. The external capacitor values required for
this IC are so small that it allows for compact and
reliable set design.
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Package
Features
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Power Supply Voltage Range:
4V to 18V
Quiescent Current:
9.0mA (Typ)
High Common-mode Rejection Ratio(1kHz):
57dB (Typ)
Low Noise:
VNO = 3.5µVrms(Typ)
Low Distortion:
THD = 0.002% (Typ)
Operation temperature range:
-30°C to +85°C
W(Typ) x D(Typ) x H(Max)
Large Capacitors not Required
High Common-mode Rejection Ratio
Low Noise
Low Distortion
Two Channels
Applications
Car audio systems
SOP8
5.00mm x 6.20mm x 1.71mm
Typical Application Circuit
○Product structure:Silicon monolithic integrated circuit
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BA3121F
Block Diagram and Pin Configuration
TOP VIEW
VM1
VM2
Absolute Maximum Ratings (Ta = 25C)
Parameter
Power Supply Voltage
Power Dissipation
Operation Temperature
Storage Temperature
Symbol
Limit
Unit
VCC
Pd
Topr
Tstg
18
0.45 (Note 1)
-30 to +85
-55 to +125
V
W
°C
°C
(Note 1) Reduced by 4.5mW in Ta of 1°C over 25°C .
Caution: Operating the IC over the absolute maximum ratings may damage the IC. The damage can either be a short circuit between pins or an open circuit
between pins and the internal circuitry. Therefore, it is important to consider circuit protection measures, such as adding a fuse, in case the IC is operated over
the absolute maximum ratings.
Recommended Operating Conditions (Ta = 25C)
Parameter
Symbol
Min
Typ
Max
Unit
Power Supply Voltage
VCC
4
12
18
V
Electrical Characteristics
(Unless otherwise noted, Ta = 25C, VCC = 12V, f = 1kHz, Rg = 1.8kΩ)
Symbol
Min
Typ
Max
Unit
Quiescent Current
Output Noise Voltage
IQ
VNO
5.6
-
9.0
3.5
14.0
8.0
mA
μVrms
Voltage Gain
GV
-1.5
-0.04
+1.5
dB
Maximum Output Voltage
VOM
1.8
2.0
-
Vrms
Parameter
THD
-
0.002
0.02
%
CMRR
41
57
-
dB
Common-made Voltage
VCM
2.5
3.75
-
Vrms
Ripple Rejection Ratio
RR
72
80
-
dB
Channel Separation
CS
-
82
-
dB
Slew Rate
Input Resistance
SR
RIN
44
2.0
55
66
V/μS
kΩ
Total Harmonic Distortion
Common-mode Rejection Ratio
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Conditions
VIN=0Vrms
BPF=20Hz-20kHz
VOUT=-10dBm, Rg=0Ω
THD=0.1%, VCC=8V
VOUT=0.7Vrms
VCC=8V,CMRR=40dB
fRR=100Hz,VRR=-10dBm,
Rg=0Ω
VIN=-10dBm,
Rg=1.8kΩ/OPEN
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BA3121F
Typical Performance Curves
Quiescent Current : IQ (mA)
Maximum Output Voltage : VOM (Vrms)
VIN = 0Vrms
Power Supply Voltage : VCC (V)
Power Supply Voltage : VCC (V)
Figure 1. Quiescent Current vs
Power Supply Voltage
Figure 2. Maximum Output Voltage vs
Power Supply Voltage
Voltage Gain : GV (dB)
Output Noise Voltage : VNO (µVrms)
THD=0.1%
RL = 10kΩ
f=1kHz
Power Supply Voltage : VCC (V)
Power Supply Voltage : VCC (V)
Figure 4. Voltage Gain vs Power Supply Voltage
Figure 3. Output Noise Voltage vs Power Supply
Voltage
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BA3121F
Typical Performance Curves – continued
Voltage Gain : GV (dB)
Channel Separation : CS (dB)
VCC = 12V
VIN=-10dBm
10 20
50 100 200 500 1k 2k
VCC=12V
VIN = -10dBm
Rg=1.8kΩ/Open
RL=10kΩ
10 20
5k 10k 20k
50 100 200 500 1k 2k
Frequency : f (Hz)
Figure 6. Channel Separation vs Frequency
VCC = 12V
VRR=-10dBm
Rg=0Ω
RL=10kΩ
50 100 200 500 1k 2k
Total Harmonic Distortion : THD (%)
Ripple Rejection Ratio : RR (dB)
Figure 5. Voltage Gain vs Frequency
10 20
VCC = 12V
f=1kHz
RL=10kΩ
5k 10k 20k
Output Voltage : VOUT (Vrms)
Frequency : f (Hz)
Figure 8. Total Harmonic Distortion vs Output
Voltage
Figure 7. Ripple Rejection Ratio vs Frequency
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5k 10k 20k
Frequency : f (Hz)
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BA3121F
Common Mode Rejection Ratio : CMRR (dB)
Typical Performance Curves – continued
Total Harmonic Distortion : THD (%)
VCC = 12V
VOUT = 0.7Vrms
RL= 10kΩ
10 20
50 100 200 500 1k 2k 5k 10k 20k
Frequency : f (Hz)
Common Mode Rejection Ratio : CMRR (dB)
Figure 9. Total Harmonic Distortion vs Frequency
VCC = 12V
VN=-20dBm
Rg=1.8kΩ
(VM1, VM2)=(100µF, 47µF)
(VM1, VM2)=(47µF, 22µF)
(VM1, VM2)=(22µF, 10µF)
10 20 50 100 200 500 1k 2k
5k 10k 20k
Frequency : f (Hz)
Figure 10. Common Mode Rejection Ratio vs Frequency
VCC = 8V
f=1kHz
Rg=1.8kΩ
Input Noise Voltage : VCM (Vrms)
Figure 11. Common Mode Rejection Ratio vs Input Noise
Voltage
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BA3121F
Measurement Circuits
BA3121F
Figure 12
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BA3121F
Application Information
1.
Circuit Operation
Figure 13. Flow of Noise in Car Audio Systems
Car audio systems are grounded to the car body. For
this reason, electrical noise generated by the car
electrical system can enter the power amplifier input
through the chassis and become audible.
BA3121F utilizes the common-mode rejection
characteristics of an operational amplifier to eliminate
this noise. Without BA3121F noise enters the power
amplifier inputs directly. With BA3121F, the CMRR of
operational amplifiers 1-A and 2-A eliminates the noise.
Principle of noise elimination:
To obtain the output voltage (eO)
Figure 14. The Principle of Noise Rejection
R4
Vi 
e
R3  R4  2
eO  
R2
R  R2
e1  1
 Vi
R1
R1
①
②
With BA3121F, the elimination level of
the noise is expressed as:
CMRR = 20log (eO/eI)(eI = e1 = e2)
Therefore, CMRR ≥ 41dB can be guaranteed.
From ① and ②
R2
R  R2
R4
e1  1

 e2
R1
R1
( R3  R4 )
eO  
-
R2
R R - R2 R3
 e1 - e2   1 4
 e2
R1
R1 ( R3  R4 )
Ideally, if R1R4 = R2R3, and e1 = e2, the noise voltage will
be zero. However, due to resistor mismatch, difference in the noise voltages (e1 and e2),
and tolerances in the operational amplifier, a noise voltage is generated.
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BA3121F
Operational Notes
1.
Reverse Connection of Power Supply
Connecting the power supply in reverse polarity can damage the IC. Take precautions against reverse polarity when
connecting the power supply, such as mounting an external diode between the power supply and the IC’s power
supply pins.
2.
Power Supply Lines
Design the PCB layout pattern to provide low impedance supply lines. Separate the ground and supply lines of the
digital and analog blocks to prevent noise in the ground and supply lines of the digital block from affecting the analog
block. Furthermore, connect a capacitor to ground at all power supply pins. Consider the effect of temperature and
aging on the capacitance value when using electrolytic capacitors.
3.
Ground Voltage
Ensure that no pins are at a voltage below that of the ground pin at any time, even during transient condition.
4.
Ground Wiring Pattern
When using both small-signal and large-current ground traces, the two ground traces should be routed separately but
connected to a single ground at the reference point of the application board to avoid fluctuations in the small-signal
ground caused by large currents. Also ensure that the ground traces of external components do not cause variations
on the ground voltage. The ground lines must be as short and thick as possible to reduce line impedance.
5.
Thermal Consideration
Should by any chance the power dissipation rating be exceeded the rise in temperature of the chip may result in
deterioration of the properties of the chip. In case of exceeding this absolute maximum rating, increase the board size
and copper area to prevent exceeding the Pd rating.
6.
Recommended Operating Conditions
These conditions represent a range within which the expected characteristics of the IC can be approximately obtained.
The electrical characteristics are guaranteed under the conditions of each parameter.
7.
Inrush Current
When power is first supplied to the IC, it is possible that the internal logic may be unstable and inrush current may flow
instantaneously due to the internal powering sequence and delays, especially if the IC has more than one power
supply. Therefore, give special consideration to power coupling capacitance, power wiring, width of ground wiring, and
routing of connections.
8.
Operation Under Strong Electromagnetic Field
Operating the IC in the presence of a strong electromagnetic field may cause the IC to malfunction.
9.
Testing on Application Boards
When testing the IC on an application board, connecting a capacitor directly to a low-impedance output pin may
subject the IC to stress. Always discharge capacitors completely after each process or step. The IC’s power supply
should always be turned off completely before connecting or removing it from the test setup during the inspection
process. To prevent damage from static discharge, ground the IC during assembly and use similar precautions during
transport and storage.
10. Inter-pin Short and Mounting Errors
Ensure that the direction and position are correct when mounting the IC on the PCB. Incorrect mounting may result in
damaging the IC. Avoid nearby pins being shorted to each other especially to ground, power supply and output pin.
Inter-pin shorts could be due to many reasons such as metal particles, water droplets (in very humid environment) and
unintentional solder bridge deposited in between pins during assembly to name a few.
11. Unused Input Pins
Input pins of an IC are often connected to the gate of a MOS transistor. The gate has extremely high impedance and
extremely low capacitance. If left unconnected, the electric field from the outside can easily charge it. The small charge
acquired in this way is enough to produce a significant effect on the conduction through the transistor and cause
unexpected operation of the IC. So unless otherwise specified, unused input pins should be connected to the power
supply or ground line.
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BA3121F
Operational Notes – continued
12. Regarding the Input Pin of the IC
This monolithic IC contains P+ isolation and P substrate layers between adjacent elements in order to keep them
isolated. P-N junctions are formed at the intersection of the P layers with the N layers of other elements, creating a
parasitic diode or transistor. For example (refer to figure below):
When GND > Pin A and GND > Pin B, the P-N junction operates as a parasitic diode.
When GND > Pin B, the P-N junction operates as a parasitic transistor.
Parasitic diodes inevitably occur in the structure of the IC. The operation of parasitic diodes can result in mutual
interference among circuits, operational faults, or physical damage. Therefore, conditions that cause these diodes to
operate, such as applying a voltage lower than the GND voltage to an input pin (and thus to the P substrate) should be
avoided.
Resistor
Transistor (NPN)
Pin A
Pin B
C
E
Pin A
N
P+
P
N
N
P+
N
Pin B
B
N
Parasitic
Elements
P+
N P
N
P+
B
N
C
E
Parasitic
Elements
P Substrate
P Substrate
GND
GND
Parasitic
Elements
GND
Parasitic
Elements
GND
N Region
close-by
Figure 15. Example of monolithic IC structure
13. The capacitors of Pin2 (VM1), and Pin 6 (VM2) should maintain the ratio of 2:1 for ripple rejection characteristics.
Maintaining this ratio will prevent the significant decrease on ripple rejection even if the capacitance is reduced to half.
14. Setting the capacitor value to twice or half will make CMRR +6dB or -6dB respectively (Figure 10) in the low frequency
range.
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BA3121F
Ordering Information
B
A
3
1
2
1
F
-
E2
Package
F: SOP8
Part Number
Packaging and forming specification
E2: Embossed tape and reel
Marking Diagram
SOP8 (TOP VIEW)
Part Number Marking
3
1
2
1
LOT Number
1PIN MARK
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BA3121F
Physical Dimension, Tape and Reel Information
Package Name
SOP8
(Max 5.35 (include.BURR))
(UNIT : mm)
PKG : SOP8
Drawing No. : EX112-5001-1
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BA3121F
Revision History
Date
Revision
13.Nov.2015
001
Changes
New Release
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Datasheet
Notice
Precaution on using ROHM Products
1.
Our Products are designed and manufactured for application in ordinary electronic equipments (such as AV equipment,
OA equipment, telecommunication equipment, home electronic appliances, amusement equipment, etc.). If you
(Note 1)
, transport
intend to use our Products in devices requiring extremely high reliability (such as medical equipment
equipment, traffic equipment, aircraft/spacecraft, nuclear power controllers, fuel controllers, car equipment including car
accessories, safety devices, etc.) and whose malfunction or failure may cause loss of human life, bodily injury or
serious damage to property (“Specific Applications”), please consult with the ROHM sales representative in advance.
Unless otherwise agreed in writing by ROHM in advance, ROHM shall not be in any way responsible or liable for any
damages, expenses or losses incurred by you or third parties arising from the use of any ROHM’s Products for Specific
Applications.
(Note1) Medical Equipment Classification of the Specific Applications
JAPAN
USA
EU
CHINA
CLASSⅢ
CLASSⅡb
CLASSⅢ
CLASSⅢ
CLASSⅣ
CLASSⅢ
2.
ROHM designs and manufactures its Products subject to strict quality control system. However, semiconductor
products can fail or malfunction at a certain rate. Please be sure to implement, at your own responsibilities, adequate
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a failure or malfunction of our Products may cause. The following are examples of safety measures:
[a] Installation of protection circuits or other protective devices to improve system safety
[b] Installation of redundant circuits to reduce the impact of single or multiple circuit failure
3.
Our Products are designed and manufactured for use under standard conditions and not under any special or
extraordinary environments or conditions, as exemplified below. Accordingly, ROHM shall not be in any way
responsible or liable for any damages, expenses or losses arising from the use of any ROHM’s Products under any
special or extraordinary environments or conditions. If you intend to use our Products under any special or
extraordinary environments or conditions (as exemplified below), your independent verification and confirmation of
product performance, reliability, etc, prior to use, must be necessary:
[a] Use of our Products in any types of liquid, including water, oils, chemicals, and organic solvents
[b] Use of our Products outdoors or in places where the Products are exposed to direct sunlight or dust
[c] Use of our Products in places where the Products are exposed to sea wind or corrosive gases, including Cl2,
H2S, NH3, SO2, and NO2
[d] Use of our Products in places where the Products are exposed to static electricity or electromagnetic waves
[e] Use of our Products in proximity to heat-producing components, plastic cords, or other flammable items
[f] Sealing or coating our Products with resin or other coating materials
[g] Use of our Products without cleaning residue of flux (even if you use no-clean type fluxes, cleaning residue of
flux is recommended); or Washing our Products by using water or water-soluble cleaning agents for cleaning
residue after soldering
[h] Use of the Products in places subject to dew condensation
4.
The Products are not subject to radiation-proof design.
5.
Please verify and confirm characteristics of the final or mounted products in using the Products.
6.
In particular, if a transient load (a large amount of load applied in a short period of time, such as pulse. is applied,
confirmation of performance characteristics after on-board mounting is strongly recommended. Avoid applying power
exceeding normal rated power; exceeding the power rating under steady-state loading condition may negatively affect
product performance and reliability.
7.
De-rate Power Dissipation depending on ambient temperature. When used in sealed area, confirm that it is the use in
the range that does not exceed the maximum junction temperature.
8.
Confirm that operation temperature is within the specified range described in the product specification.
9.
ROHM shall not be in any way responsible or liable for failure induced under deviant condition from what is defined in
this document.
Precaution for Mounting / Circuit board design
1.
When a highly active halogenous (chlorine, bromine, etc.) flux is used, the residue of flux may negatively affect product
performance and reliability.
2.
In principle, the reflow soldering method must be used on a surface-mount products, the flow soldering method must
be used on a through hole mount products. If the flow soldering method is preferred on a surface-mount products,
please consult with the ROHM representative in advance.
For details, please refer to ROHM Mounting specification
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Datasheet
Precautions Regarding Application Examples and External Circuits
1.
If change is made to the constant of an external circuit, please allow a sufficient margin considering variations of the
characteristics of the Products and external components, including transient characteristics, as well as static
characteristics.
2.
You agree that application notes, reference designs, and associated data and information contained in this document
are presented only as guidance for Products use. Therefore, in case you use such information, you are solely
responsible for it and you must exercise your own independent verification and judgment in the use of such information
contained in this document. ROHM shall not be in any way responsible or liable for any damages, expenses or losses
incurred by you or third parties arising from the use of such information.
Precaution for Electrostatic
This Product is electrostatic sensitive product, which may be damaged due to electrostatic discharge. Please take proper
caution in your manufacturing process and storage so that voltage exceeding the Products maximum rating will not be
applied to Products. Please take special care under dry condition (e.g. Grounding of human body / equipment / solder iron,
isolation from charged objects, setting of Ionizer, friction prevention and temperature / humidity control).
Precaution for Storage / Transportation
1.
Product performance and soldered connections may deteriorate if the Products are stored in the places where:
[a] the Products are exposed to sea winds or corrosive gases, including Cl2, H2S, NH3, SO2, and NO2
[b] the temperature or humidity exceeds those recommended by ROHM
[c] the Products are exposed to direct sunshine or condensation
[d] the Products are exposed to high Electrostatic
2.
Even under ROHM recommended storage condition, solderability of products out of recommended storage time period
may be degraded. It is strongly recommended to confirm solderability before using Products of which storage time is
exceeding the recommended storage time period.
3.
Store / transport cartons in the correct direction, which is indicated on a carton with a symbol. Otherwise bent leads
may occur due to excessive stress applied when dropping of a carton.
4.
Use Products within the specified time after opening a humidity barrier bag. Baking is required before using Products of
which storage time is exceeding the recommended storage time period.
Precaution for Product Label
QR code printed on ROHM Products label is for ROHM’s internal use only.
Precaution for Disposition
When disposing Products please dispose them properly using an authorized industry waste company.
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Since concerned goods might be fallen under listed items of export control prescribed by Foreign exchange and Foreign
trade act, please consult with ROHM in case of export.
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1.
All information and data including but not limited to application example contained in this document is for reference
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other rights of any third party regarding such information or data.
2.
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3.
No license, expressly or implied, is granted hereby under any intellectual property rights or other rights of ROHM or any
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Other Precaution
1.
This document may not be reprinted or reproduced, in whole or in part, without prior written consent of ROHM.
2.
The Products may not be disassembled, converted, modified, reproduced or otherwise changed without prior written
consent of ROHM.
3.
In no event shall you use in any way whatsoever the Products and the related technical information contained in the
Products or this document for any military purposes, including but not limited to, the development of mass-destruction
weapons.
4.
The proper names of companies or products described in this document are trademarks or registered trademarks of
ROHM, its affiliated companies or third parties.
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Datasheet
General Precaution
1. Before you use our Pro ducts, you are requested to care fully read this document and fully understand its contents.
ROHM shall n ot be in an y way responsible or liabl e for fa ilure, malfunction or acci dent arising from the use of a ny
ROHM’s Products against warning, caution or note contained in this document.
2. All information contained in this docume nt is current as of the issuing date and subj ect to change without any prior
notice. Before purchasing or using ROHM’s Products, please confirm the la test information with a ROHM sale s
representative.
3.
The information contained in this doc ument is provi ded on an “as is” basis and ROHM does not warrant that all
information contained in this document is accurate an d/or error-free. ROHM shall not be in an y way responsible or
liable for an y damages, expenses or losses incurred b y you or third parties resulting from inaccur acy or errors of or
concerning such information.
Notice – WE
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