LM4780TA/NOPB National Semiconductor, LM4780TA/NOPB Datasheet - Page 16

• Manufacturer Part Number: LM4780TA/NOPB
• Description: IC AMP AUDIO PWR 60W AB TO220-27
• Manufacturer: National Semiconductor
• Series: Overture™r
• Type: Class ABr

Specifications of LM4780TA/NOPB

• Output Type: 2-Channel (Stereo)
• Max Output Power X Channels @ Load: 60W x 2 @ 8 Ohm
• Voltage - Supply: 20 V ~ 84 V, ±10 V ~ 42 V
• Features: Depop, Mute, Short-Circuit and Thermal Protection
• Mounting Type: Through Hole
• Package / Case: TO-220-27 (Bent and Staggered Leads)
• Amplifier Class: AB
• No. Of Channels: 2
• Output Power: 60W
• Supply Voltage Range: 20V To 84V
• Load Impedance: 8ohm
• Operating Temperature Range: -20°C To +85°C
• Amplifier Case Style: TO-220
• Rohs Compliant: Yes
• For Use With: LM4780TABD - BOARD EVALUATION LM4780TA
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: *LM4780TA; *LM4780TA/NOPB; LM4780TA

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Application Information
MUTE MODE
The muting function allows the user to mute the amplifier. This
can be accomplished as shown in the Typical Application Cir-
cuit. The resistor R
supply voltage and is used in conjunction with a switch. The
switch, when opened or switched to GND, cuts off the current
flow from the MUTE pins to −V
into mute mode. Refer to the Mute Attenuation vs Mute Cur-
rent curves in the Typical Performance Characteristics
section for values of attenuation per current out of each MUTE
pin. The resistance R
Where I
The MUTE pins can be tied together so that only one resistor
is required for the mute function. The mute resistor value must
be chosen so that a minimum of 1mA is pulled through the
resistor R
tional. Taking into account supply line fluctuations, it is a good
idea to pull out 1mA per MUTE pin or 2mA total if both pins
are tied together.
A turn-on MUTE or soft start circuit may also be used during
power up. A simple circuit like the one shown below may be
used.
The RC combination of C
point A to change more slowly than the -V
Until the voltage at point A is low enough to have 0.5mA of
current per MUTE pin flow through R
mode. The series combination of R
isfy the mute equation above for all operating voltages or mute
mode may be activated during normal operation. For a longer
turn-on mute time, a larger time constant, τ = RC = R
(sec), is needed. For the values show above and with the
MUTE pins tied together, the LM4780 will enter play mode
when the voltage at point A is -17.6V. The voltage at point A
is found with Equation (1) below.
where:
τ = RC (sec)
UNDER-VOLTAGE PROTECTION
Upon system power-up, the under-voltage protection circuitry
allows the power supplies and their corresponding capacitors
to come up close to their full values before turning on the
LM4780. Since the supplies have essentially settled to their
final value, no DC output spikes occur. At power down, the
outputs of the LM4780 are forced to ground before the power
t = time (sec)
V
V
o
f
= Final voltage, -V
= Voltage on C at t = 0 (Volts)
MUTE
M
. This ensures that each amplifier is fully opera-
≥
V
0.5mA for each MUTE pin.
A
R
(t) = (V
M
M
≤
is chosen with reference to the negative
M
(|−V
is calculated by the following equation:
EE
f
- V
M
in this circuit (Volts)
EE
and R
O
| − 2.6V) / I
)e
-t/τ
EE
M1
(Volts)
, thus placing the LM4780
M1
may cause the voltage at
M2
and R
, the IC will be in mute
MUTE
EE
M2
supply voltage.
needs to sat-
200586a3
M1
C
(1)
M
16
supply voltages fully decay preventing transients on the out-
put.
OVER-VOLTAGE PROTECTION
The LM4780 contains over-voltage protection circuitry that
limits the output current while also providing voltage clamp-
ing. The clamp does not, however, use internal clamping
diodes. The clamping effect is quite the same because the
output transistors are designed to work alternately by sinking
large current spikes.
SPiKe PROTECTION
The LM4780 is protected from instantaneous peak-tempera-
ture stressing of the power transistor array. The Safe Oper-
ating graph in the Typical Performance Characteristics
section shows the area of device operation where SPiKe
Protection Circuitry is not enabled. The SPiKe Protection Re-
sponse waveform graph shows the waveform distortion when
SPiKe is enabled. Please refer to AN-898 for more detailed
information.
THERMAL PROTECTION
The LM4780 has a sophisticated thermal protection scheme
to prevent long-term thermal stress of the device. When the
temperature on the die exceeds 150°C, the LM4780 shuts
down. It starts operating again when the die temperature
drops to about 145°C, but if the temperature again begins to
rise, shutdown will occur again above 150°C. Therefore, the
device is allowed to heat up to a relatively high temperature
if the fault condition is temporary, but a sustained fault will
cause the device to cycle in a Schmitt Trigger fashion be-
tween the thermal shutdown temperature limits of 150°C and
145°C. This greatly reduces the stress imposed on the IC by
thermal cycling, which in turn improves its reliability under
sustained fault conditions.
Since the die temperature is directly dependent upon the heat
sink used, the heat sink should be chosen so that thermal
shutdown is not activated during normal operation. Using the
best heat sink possible within the cost and space constraints
of the system will improve the long-term reliability of any pow-
er semiconductor device, as discussed in the Determining
the Correct Heat Sink section.
DETERMlNlNG MAXIMUM POWER DISSIPATION
Power dissipation within the integrated circuit package is a
very important parameter requiring a thorough understanding
if optimum power output is to be obtained. An incorrect max-
imum power dissipation calculation may result in inadequate
heat sinking causing thermal shutdown and thus limiting the
output power.
Equation 2
point of each amplifier in a single-ended configuration where
V
Thus by knowing the total supply voltage and rated output
load, the maximum power dissipation point can be calculated.
The package dissipation is twice the number which results
from
LM4780. Refer to the graphs of Power Dissipation versus
Output Power in the Typical Performance Characteristics
section which show the actual full range of power dissipation
not just the maximum theoretical point that results from
tion
CC
2.
is the total supply voltage.
Equation 2
shows the theoretical maximum power dissipation
P
DMAX
since there are two amplifiers in each
= (V
CC
)
2
/ 2
π
2
R
L
Equa-
(2)