Technical Note
28/30
BD5446EFV
www.rohm.com
2010.05 - Rev.B
© 2010 ROHM Co., Ltd. All rights reserved.
●
Notes for use
1 ) Absolute maximum ratings
Use of the IC in excess of absolute maximum ratings such as the applied voltage or operating temperature range may
result in IC damage. Assumptions should not be made regarding the state of the IC (short mode or open mode) when
such damage is suffered. A physical safety measure such as a fuse should be implemented when use of the IC in a
special mode where the absolute maximum ratings may be exceeded is anticipated.
2 ) Power supply lines
As return of current regenerated by back EMF of output coil happens, take steps such as putting capacitor between
power supply and GND as a electric pathway for the regenerated current. Be sure that there is no problem with each
property such as emptied capacity at lower temperature regarding electrolytic capacitor to decide capacity value. If the
connected power supply does not have sufficient current absorption capacity, regenerative current will cause the voltage
on the power supply line to rise, which combined with the product and its peripheral circuitry may exceed the absolute
maximum ratings. It is recommended to implement a physical safety measure such as the insertion of a voltage clamp
diode between the power supply and GND pins.
3 ) GND potential(Pin 6, 36, 37, 45, 46).
Any state must become the lowest voltage about GND terminal and VSS terminal.
4 ) Input terminal
The parasitic elements are formed in the IC because of the voltage relation. The parasitic element operating causes the
wrong operation and destruction. Therefore, please be careful so as not to operate the parasitic elements by impressing
to input terminals lower voltage than GND and VSS. Please do not apply the voltage to the input terminal when the
power-supply voltage is not impressed.
5 ) Setting of heat
Use a thermal design that allows for a sufficient margin in light of the power dissipation (Pd) in actual operating conditions.
This IC exposes its frame of the backside of package. Note that this part is assumed to use after providing heat
dissipation treatment to improve heat dissipation efficiency. Try to occupy as wide as possible with heat dissipation
pattern not only on the board surface but also the backside.
Class D speaker amplifier is high efficiency and low heat generation by comparison with conventional Analog power
amplifier. However, In case it is operated continuously by maximum output power, Power dissipation (Pdiss) may exceed
package dissipation. Please consider about heat design that Power dissipation (Pdiss) does not exceed Package
dissipation (Pd) in average power (Poav). (Tjmax : Maximum junction temperature=150
℃
, Ta : Peripheral temperature[
℃
],
θ
ja : Thermal resistance of package[
℃
/W], Poav : Average power[W],
η
: Efficiency)
Package dissipation : Pd(W)=(Tjmax - Ta)/
θ
ja
Power dissipation : Pdiss(W)= Poav
×
(1/
η
- 1)
6 ) Actions in strong magnetic field
Use caution when using the IC in the presence of a strong magnetic field as doing so may cause the IC to malfunction.
7 ) Thermal shutdown circuit
This product is provided with a built-in thermal shutdown circuit. When the thermal shutdown circuit operates, the output
transistors are placed under open status. The thermal shutdown circuit is primarily intended to shut down the IC avoiding
thermal runaway under abnormal conditions with a chip temperature exceeding Tjmax = 150
℃
.
8 ) Shorts between pins and misinstallation
When mounting the IC on a board, pay adequate attention to orientation and placement discrepancies of the IC. If it is
misinstalled and the power is turned on, the IC may be damaged. It also may be damaged if it is shorted by a foreign
substance coming between pins of the IC or between a pin and a power supply or a pin and a GND.
9 ) Power supply on/off (Pin 25, 28, 29, 53, 54)
In case power supply is started up, RESETX(Pin 12), MUTEX(Pin 13) and PDX (Pin 14) always should be set Low. And
in case power supply is shut down, it should be set Low likewise. Then it is possible to eliminate pop noise when power
supply is turned on/off. And also, all power supply terminals should start up and shut down together.
10 ) ERROR terminal(Pin 24)
A error flag is outputted when Output short protection and DC voltage protection in the speaker are operated. These flags
are the function which the condition of this product is shown in.
11 ) N.C. terminal(Pin 26, 30, 34, 35, 41, 47, 48, 52)
N.C. terminal (Non Connection Pin) does not connect to the inside circuit. Therefore, possible to use open.
12 ) TEST terminal(Pin 19, 20)
TEST terminal connects with ground to prevent the malfunction by external noise.
13 ) Precautions for Spealer-setting
If the impedance characteristics of the speakers at high-frequency range while increase rapidly, the IC might not have
stable-operation in the resonance frequency range of the LC-filter. Therefore, consider adding damping-circuit, etc.,
depending on the impedance of the speaker.
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