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PDF LM4652 Data sheet ( Hoja de datos )
| Número de pieza | LM4652 | |
| Descripción | LM4651 & LM4652 Overture Audio Power Amplifier 170W Class D Audio Power Amplifier Solution | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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August 2000
LM4651 & LM4652 Overture™ Audio Power Amplifier
170W Class D Audio Power Amplifier Solution
General Description
The IC combination of the LM4651 driver and the LM4652
power MOSFET provides a high efficiency, Class D sub-
woofer amplifier solution.
The LM4651 is a fully integrated conventional pulse width
modulator driver IC. The IC contains short circuit, under
voltage, over modulation, and thermal shut down protection
circuitry. It contains a standby function, which shuts down
the pulse width modulation and minimizes supply current.
The LM4652 is a fully integrated H-bridge power MOSFET
IC in a TO-220 power package. Together, these two IC’s
form a simple, compact high power audio amplifier solution
complete with protection normally seen only in Class AB
amplifiers. Few external components and minimal traces
between the IC’s keep the PCB area small and aids in EMI
control.
The near rail-to-rail switching amplifier substantially in-
creases the efficiency compared to Class AB amplifiers. This
high efficiency solution significantly reduces the heat sink
size compared to a Class AB IC of the same power level.
This two-chip solution is optimum for powered subwoofers
and self powered speakers.
Key Specifications
n Output power into 4Ω with < 10% THD. 170W (Typ)
n THD at 10W, 4Ω, 10 − 500Hz.
< 0.3% THD (Typ)
n Maximum efficiency at 125W
n Standby attenuation.
85% (Typ)
>100dB (Min)
Features
n Conventional pulse width modulation.
n Externally controllable switching frequency.
n 50kHZ to 200kHz switching frequency range.
n Integrated error amp and feedback amp.
n Turn−on soft start and under voltage lockout.
n Over modulation protection (soft clipping).
n Short circuit current limiting and thermal shutdown
protection.
n 15 Lead TO−220 isolated package.
n Self checking protection diagnostic.
Applications
n Powered subwoofers for home theater and PC’s
n Car booster amplifier
n Self-powered speakers
Connection Diagrams
LM4651 Plastic Package
LM4652 Plastic Package (Note 8)
DS101277-72
Top View
Order Number LM4651N
See NS Package Number N28B
Overture® is a registered trademark of National Semiconductor Corporation.
© 2001 National Semiconductor Corporation DS101277
DS101277-73
Isolated TO-220 Package
Order Number LM4652TF
See NS Package Number TF15B
or
Non-Isolated TO-220 Package
Order Number LM4652TA
See NS Package Number TA15A
www.national.com
1 page  
LM4651 Pin Descriptions
Pin No.
1
2,27
3
4
5,15
6
7
8
9
10
11
12
13
14
16
17
18
19
20,21
22,23
24
25
26
28
Symbol
OUT1
BS1,BS2
HG1
HG2
GND
+6VBYP
+VCC
−6VBYP
FBKVO
ERRIN
ERRVO
TSD
STBY
FBK1
OSC
Delay
SCKT
FBK2
−VDDBYP
−VEE
START
LG1
LG2
OUT2
Description
The reference pin of the power MOSFET output to the gate drive circuitry.
The bootstrap pin provides extra bias to drive the upper gates, HG1,HG2.
High−Gate #1 is the gate drive to a top side MOSFET in the H-Bridge.
High−Gate #2 is the gate drive to a top side MOSFET in the H-Bridge.
The ground pin for all analog circuitry.
The internally regulated positive voltage output for analog circuitry. This pin is available
for internal regulator bypassing only.
The positive supply input for the IC.
The internally regulated negative voltage output for analog circuitry. This pin is available
for internal regulator bypassing only.
The feedback instrumentation amplifier output pin.
The error amplifier inverting input pin. The input audio signal and the feedback signal are
summed at this input pin.
The error amplifier output pin.
The thermal shut down input pin for the thermal shut down output of the LM4652.
Standby function input pin. This pin is CMOS compatible.
The feedback instrumentation amplifier pin. This must be connected to the feedback filter
from VO1 (pin 15 on the LM4652 ).
The switching frequency oscillation pin. Adjusting the resistor from 15.5kΩ to 0Ω
changes the switching frequency from 75kHz to 225kHz.
The dead time setting pin.
Short circuit setting pin. Minimum setting is 10A.
The feedback instrumentation amplifier pin. This must be connected to the feedback filter
from VO2 (pin 7 on the LM4652 ).
The regulator output for digital blocks. This pin is for bypassing only.
The negative voltage supply pin for the IC.
The start up capacitor input pin. This capacitor adjusts the start up time of the diagnostic
sequence for the modulator. Refer to Start up Sequence and Timing in the
Application Information section.
Low−Gate #1 is the gate drive to a bottom side MOSFET in the H-Bridge.
Low−Gate #2 is the gate drive to a bottom side MOSFET in the H-Bridge.
The reference pin of the power MOSFET output to the gate drive circuitry.
5 www.national.com
5 Page 
Application Information (Continued)
reduced as the desired bandwidth of operation increases.
The dead time can be adjusted with the RDLY resistor by
Equation (4):
TDLY = 1.7x10−12 (500 + RDLY) (Seconds) (4)
Currently, the recommended value is 5kΩ.
Oscillator Control: The modulation frequency is set by an
external resistor, ROSC, connected between pin 16 and
GND. The modulation frequency can be set within the range
of 50kHz to 225kHz according to the design requirements.
The values of ROSC and fOSC can be found by Equation (5)
and (6):
fOSC = 1x109/ (4000 + ROSC)
ROSC = (1x109/ fOSC) − 4000
(Hz)
(Ω)
(5)
(6)
Equations (5) and (6) are for RDLY = 0. Using a value of RDLY
greater than zero will increase the value needed for ROSC.
For RDLY = 5kΩ, ROSC will need to be increased by about
2kΩ. As the graphs show, increasing the switching frequency
will reduce the THD but also decreases the efficiency and
maximum output power level before clipping. Increasing the
switching frequency increases the amount of loss because
switching currents lower the efficiency across the output
power range. A higher switching frequency also lowers the
maximum output power before clipping or the 1% THD point
occur.
Over-Modulation Protection: The over-modulation protec-
tion is an internally generated fixed pulse width signal that
prevents any side of the H-bridge power MOSFETs from
remaining active for an extended period of time. This condi-
tion can result when the input signal amplitude is higher than
the internal triangle waveform. Lack of an over modulation
signal can increase distortion when the amplifier’s output is
clipping. Figure 4 shows how the over modulation protection
works.
DS101277-2
FIGURE 4. Over Modulation Protection
The over modulation protection also provides a ’soft clip’
type response on the top of a sine wave. This minimum
pulse time is internally set and cannot be adjusted. As the
switching frequency increases this minimum time becomes a
higher percentage of the period (TPERIOD = 1/fSW). Because
the over modulation protection time is a higher percentage of
the period, the peak output voltage is lower and, therefore,
the output power at clipping is lower for the same given
supply rails and load.
Feedback Amplifier and Filter: The purpose of the feed-
back amplifier is to differentially sample the output and pro-
vide a single-ended feedback signal to the error amplifier to
close the feedback loop. The feedback is taken directly from
the switching output before the demodulating LC filter to
avoid the phase shift caused by the output filter. The signal
fed back is first low pass filtered with a single pole or dual
pole RC filter to remove the switching frequency and its
harmonics. The differential signal, derived from the bridge
output, goes into the high input impedance instrumentation
amplifier that is used as the feedback amplifier. The instru-
mentation amplifier has an internally fixed gain of 1. The use
of an instrumentation amplifier serves two purposes. First,
it’s input are high impedance so it doesn’t load down the
output stage. Secondly, an IA has excellent common-mode
rejection when its gain setting resistors are properly
matched. This feature allows the IA to derive the true feed-
back signal from the differential output, which aids in improv-
ing the system performance.
DS101277-3
FIGURE 5. Feedback instrumentation Amplifier
Schematic
Error Amplifier: The purpose of the error amplifier is to sum
the input audio signal with the feedback signal derived from
the output. This inverting amplifier’s gain is externally con-
figurable by resistors Rf and R1. The parallel feedback ca-
pacitor and resistor form a low pass filter that limits the
frequency content of the input audio signal and the feedback
signal. The pole of the filter is set by Equation (7).
fIP = 1/(2πRfCf) (Hz) (7)
On-Board Regulators: The LM4651 has its own internal
supply regulators for both analog and digital circuits. Sepa-
rate ±6V regulators exist solely for the analog amplifiers,
oscillator and PWM comparators. A separate voltage regu-
lator powers the digital logic that controls the protection,
level shifting, and high−/low−side driver circuits. System per-
formance is enhanced by bypassing each regulator’s output.
The ±6V regulator outputs, labeled +6VBYP (pin 6) and
−6VBYP (pin 8) should be bypassed to ground. The digital
regulator output, −VDDBYP (pins 20 & 21) should be by-
passed to −VEE (pins 22 & 23). The voltage level of −VDDBYP
should be always be 6V closer to ground than the negative
rail, −VEE. As an example, if −VEE = −20V, then −VDDBYP
should equal −14V. Recommended capacitor values and
type can be found in Figure 1, Typical audio Application
Circuit.
APPLICATIONS HINTS
11 www.national.com
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