170W, D audio power amplifier LM4651/LM4652

Use of National Semiconductor Corporation (NSC) announced LM4651/LM4652 Overture TM the latest IC and a few external components, can be composed of 170W high efficiency Class D audio power amplifier. LM4651 and LM4652 drives the PWM half-bridge (H-bridge) power MOSFET IC posed by such a simple compact class D subwoofer (Subwoofer) Amplifier solve the usual class AB amplifier only to see the protection, but efficiency than Class AB amplifiers have greatly improved, while the radiator size is the same power level than the Class AB amplifier has been reduced, LM4651 and LM4652 are used in home theater and PC automatically (Powered) subwoofer amplifier, car audio enhancement (booster) amplifiers, and Self is the (self-powered) speakers and so on, will yield satisfactory results.

170W, D audio power amplifier LM4651/LM4652

1 pin function

LM4651 in a 28-pin plastic package, Figure 1 (a) Top view of packaging for the LM4651. LM4652 15-pin TO-220 plastic package, divided into isolated and non-isolated two forms. Among them, the use of isolated type LM4652TF pin arrangement shown in Figure 1 (b) below.

LM4651 is a PWM control / driver IC, internal oscillator, PWM comparator, error amplifier, measuring amplifier feedback, and protect the digital logic circuits and drivers, etc. Table 1 lists the LM4651's pin functions. LM4652's pin function description as listed in Table 2.

Table 1 LM4651's pin function

Pin-pin functional description of symbols
1 OUT1 output to the power MOSFET gate drive circuit benchmark feet
1,27 BS1, BS2 to drive above the gate HG1, HG2 additional bias of the bootstrap pin
3 HG1 # 1 in the high-end half-bridge gate driver output
4 HG2 half-bridge gate driver in the # 2 high-output
5,15 GND Analog ground
6 +6 VBYP analog voltage output is within regulation, the pin only for internal regulator bypass
7 + Vcc IC positive power supply voltage input
8-6VBYP analog circuit within the regulator negative voltage output, the pin only for internal regulator bypass
9 FBKVo feedback measuring amplifier output pin
10 ERRIN error amplifier inverting input pin. The feet of the input audio signal and the feedback signal summing
11 ERRVo error amplifier output pin
12 TSD thermal shutdown input pin to connect output of LM4652's thermal shutdown
13 STBY standby input pin
14 FBK1 feedback measuring amplifier, the pin must be connected to from VO1 (LM4652 pin 15) of the feedback filter
16 OSC switching frequency oscillation feet, adjust the resistance changes from 15.5kΩ to 0Ω, the switching frequency from 75kHz to 225kHz changes
17 Delay delay time adjustment foot
18 SCKT short circuit set the feet, the minimum set value is 10A
19 FBK2 measuring amplifier feedback pin, the pin must be connected to the arrival of knowledge VO2 (LM4652's pin 7) of the feedback filter
20,21-VDDBYP used for digital cell circuit to adjust output, the pin is only used for bypass
22,23-VEE IC negative power supply voltage
24 START start capacitor input pin. Adjustable timing modulator diagnosis start-up time
25 LG1 # 1 in the low-end half-bridge gate driver output
26 LG2 # 2 in the low-end half-bridge gate driver output
28 OUT2 output to the power MOSFET gate driver circuit benchmark feet

Table 2 LM4652's pin function

Pin-pin functional description of symbols
1 GND to end
2 LG1 half-bridge low-end (# 1) MOSFET gate driver input
3 VEE supply voltage negative half-bridge power MOSFET
4 TSD Thermal Shutdown identification feet. When the chip than 150 ℃, the foot transition to 6V
5 NC Not Connected
6 LG2 half-bridge low-end (# 2) MOSFET gate driver input
7 Vo2 half-bridge - side switch output pin
8 NC not connected
9 NC Not Connected
10 HG2 half-bridge high-end (# 2) MOSFET gate driver input
11 NC Not connected
12 NC Not connected
13 Vcc is the supply voltage half-bridge power MOSFET
14 HG1 half-bridge high-end (# 1) MOSFET gate driver input
15 VO1 half-bridge - open-ended output pin

Two main parameters and characteristics

2.1 The main parameters

a. Limit parameter

LM4651/LM4652 maximum supply voltage of ± 22V, power consumption was 1.5W and 32W, the maximum junction temperature is 150 ℃, operating temperature range of -40 ~ +85 ℃. LM4652's maximum output current of 10A.

170W, D audio power amplifier LM4651/LM4652

b. Electrical Characteristics

LM4651 total quiescent current (when not connected in the LM4652 typical) to 36mA, standby state, the input voltage (typical) to 2V, the switching frequency range (in Rosc changed from 15kΩ when 0Ω) to 65 ~ 200kHz, dead District time 27ns, modulation protection time (typical) to 310ns.

LM4652 in the MOSFET's drain - source breakdown voltage of 55V, through too much resistance (typical value) of 0.2Ω, the maximum drain current (ID) for the 10A, the gate threshold voltage (typical) to 0.85V.

LM4651/LM4652 main technical parameters:

● General arrangements wave distortion (THD) (at 10W, 4Ω and under 10 ~ 500Hz) ≤ 0.3%;

● output power (4Ω, 75kHz, 10% THD pm) to 170W;

● maximum efficiency (1% THD at 125W and under) 85%;

● Standby attenuation of> 100dB.

170W, D audio power amplifier LM4651/LM4652

2.2 Features

LM4651/LM4652 The main features are as follows:

● with conventional pulse width modulation (LM46451);

● switching frequency of external control, the range of 75 ~ 200kHz;

● includes an integrated error amplifier and feedback amplifiers;

● can turn soft-start and under voltage lockout;

● with over modulation protection (soft clipping) function;

● can be short-circuit current limiting and thermal shutdown protection;

● protection of self-check diagnostic functions.

170W, D audio power amplifier LM4651/LM4652

Principle and Application Circuit 3

Figure 2 LM4651 and LM4652 Typical application and test circuit. The circuit will help people understand the two LM2651 chips, especially the function and principle.

3.1 Functional Description

LM4651 is a conventional pulse width modulator / driver IC. Figure 3 shows the input audio signal and audio signal frequency much higher than the comparison of the triangular wave signal waveform. Comparator generates a duty cycle with the audio signal level is proportional to the square wave voltage to drive the LM4652 half-bridge circuit in the power MOSFET, then the power MOSFET of the pulse sequence (frain) through the LC low-pass filter in the filter frequency applied to the speaker post.

3.2 Standby (Standby) Function

LM4651's CMOS compatibility allows the waveform to the pulse width by closing off all the power MOSFET. As the standby pulse width waveforms closed, its sound attenuation than the East 120dB, which EMI is limited to the minimum, when the pin 13 is logic "1" 5V power, the standby force; pin 13 is logic "0" or 0V When standby is invalid, allowing the use of the input signal modulation.

3.3 Start the program and timing

LM4651 has an internal soft-start function, the soft-start feature ensures system reliability and coordination of start, so turn-speaker sound (thump) or Peng Peng Sheng (pop) is minimized. Start cycle, the system remain in standby mode. Start time of the adjustment can be connected to the START pin capacitance (CSTSRT) to control.

170W, D audio power amplifier LM4651/LM4652

3.4 The current limit and short circuit protection

SCKT pin and GND connection between the resistance RSCKT used to determine the maximum output current. Once the output current is higher than the set limit, short circuit protection will shut down all power MOSFET

Minimum current limit device 10A, but the values can be appropriately adjusted RSCKT to current increases, the output short circuit or field acoustic sensor failure (short circuit), under the circumstances, IC will perform security functions.

3.5 Dead time setting

LM4651 on the DELAY pin can be used to set the system dead time. The so-called dead time is the LM4652 in a pair of MOSFET MOSFET turn-on in the other is turned off before the interval. Increase the dead time will be reduced through (Shoot through) current, but will also increase THD. With the hope that the work of the new band, dead time should be reduced. Adjust the resistance RDLY, can change the dead time, relationships are as follows:

TDLY = 1.7 × 10 12 (500 + RDLY)

The recommended value is usually RDLY 5kΩ. TDLY units in seconds.

3.6 over modulation protection

Figure 4 for the over modulation protection waveforms. When the input signal amplitude higher than the internal triangular wave, the overmodulation condition occurs, if the lack of over modulation, will result in permanent damage to the power MOSFET. In the orthodox wave at the top, over-modulation protection also provides a soft-clipping (soft clip)-type response. The same for a given voltage and load, this limiting the output power will decrease.

3.7 Feedback amplifier and filter

Samples used for differential feedback amplifier output signal and the error amplifier to provide a single-ended feedback signal, feedback signal directly from the switch before the output LC filter, thus avoiding the phase shift caused by the output filter. Differential signal output from bridge by pole or pole of the RC filter into the feedback amplifier as a high input impedance measurement using the zoom. Feedback measuring the internal fixed gain amplifier 1.

3.8 Error Amplifier

Audio input signal and feedback signal from the output sum of the error amplifier. RF amplifier gain by the external resistors R1 and decisions. Shunt feedback capacitor CF and the low-pass filter composed of resistor RF can be used to limit the audio signal and the feedback input signal frequency content.

3.9 Function of external components

The application circuit shown in Figure 2, LM4651/LM4652 Function of external key components listed in Table 3.

Table 3 shows the external component functions

Per piece function
R1, R2 input resistance, along with the RF fixed system gain: Gain = [(RF/R1) (Vcc/1.75V)] / (1 + [(RF/R1) (RF/R2) (RFL2 / (RFL1 + RFL2 )) (Vcc / T)])
RF, CF RF and CF formation of low-camel Jiang Bo device, set the error amplifier gain and bandwidth, fc = 1 / (2πRFCF) (H2) on the pole for the 3dB
RFL1 RFL1 and RFL2 feedback signal attenuation. RFL1 should 10RFL2, with see R1, R2 notes.
RFL2, CFL1 RFL2 and CFL1 produce a low-pass filter pole frequency fc = 1/2πRFL3CFL2)
CFL2 feedback path for low-pass filter to the fc = 1 / (2πRFL3CFL2) on a second pole
L1, C1 L1 and C1 to provide bipolar output point for the low-pass filter, fc = 1 / [2π (L1C1) (1 / 2)]
Cbyp and connected to the speaker at both ends for high-frequency noise and harmonic filtering
CB1 ~ CB4 Vcc, VEE, analog and digital voltage (VDD, +6 V,-6V) bypass capacitors
BBT bootstrap capacitor
RDLY set the dead time
CSTART used to control the start time; TSTART = (8.5 × 10 4) CSTART (s)
RSCKT set the output short-circuit current: ISCKT = (1 × 10 5) / (10kΩ ‖ RSCKT) (A)
ROSC control the switching frequency: fsw = (1 × 10 9) / (4000 + Rosc) (Hz)
D1 Schottky surgery tube, used to protect the output MOSFET
CSBY1 ~ CSBY3 power supply decoupling capacitor

4 Other

To further enhance the performance of D audio amplifiers, LM833 can be used to design the band pass filter and 2nd order on behalf of its gain of 10 (20dB) of the simple input stage circuit, shown in Figure 5. Applications in ultra-low noise, low-pass filter pole frequency is usually set at 60 ~ 180Hz.

It must be explained: with LM4651/LM4652 Class D amplifier is composed of PCB board should adopt the double-sided printed circuit boards.