LM48100Q-Q1

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SNAS470E – OCTOBER 2008 – REVISED NOVEMBER 2015

Table 2. Fault Detection Control Register

BIT

NAME

VALUE

DESCRIPTION

0

Normal operation

B0

OUTPUT_SHT

1

Ignore output short circuit fault (outputs shorted together)

0

Normal operation

B1

OUTPUT_OPEN

1

Ignore output short circuit fault

0

Normal operation

RAIL

B2

_SHT

1

Ignore output short to VDD or GND fault

0

Normal operation

B3

OVF

1

Ignore output over-current fault

0

Normal operation

B4

TSD

1

Ignore thermal overload fault

7.3.3 General Amplifier Function

7.3.3.1 Bridge Configuration Explained

The LM48100Q-Q1 is designed to drive a load differentially, a configuration commonly referred to as a bridge-

tied load (BTL). The BTL configuration differs from the single-ended configuration, where one side of the load is

connected to ground. A BTL amplifier offers advantages over a single-ended device. By driving the load

differentially, the output voltage is doubled, compared to a single-ended amplifier under similar conditions. This

doubling of the output voltage leads to a quadrupling of the output power. For example, the theoretical maximum

output power for a single-ended amplifier driving 8

Ω and operating from a 5 V supply is 158 mW, while the

theoretical maximum output power for a BTL amplifier operating under the same conditions is 633 mW. Since the

amplifier outputs are both biased about VDD/2, there is no net DC voltage across the load, eliminating the DC

blocking capacitors required by single-ended, single-supply amplifiers.

7.3.3.2 Input Mixer/Multiplexer

The LM48100Q-Q1 features an input mixer/multiplexer controlled through the I2C interface. The mixer/multiplexer

allows either input, or the combination of both inputs to appear at the device output. Bits B2 (INPUT_1) and B3

(INPUT_2) of the Mode Control Register select the individual input channels. Set INPUT_1 = 1 to select the

audio signal on IN1. Set INPUT_2 = 1 to select the audio signal on IN2. Setting both INPUT_1 and INPUT_2 = 1

mixes VIN1 and VIN2, and the LM48100Q-Q1 outputs the result as a mono signal (Table 3).

Table 3. Input Multiplexer Control

INPUT_1

INPUT_2

LM48100Q-Q1 OUTPUT

0

0

MUTE. No input selected

1

0

IN1 ONLY

0

1

IN2 ONLY

1

1

IN1 + IN2

7.3.4 Output Fault Detection

7.3.4.1 Output Short to Supplies (VDD or GND)

With a standard speaker load (6

Ω to 100 Ω) connected between OUTA and OUTB, the LM48100Q-Q1 can

detect a short between the outputs and either VDD or GND. A short is detected if the impedance between either

OUTA or OUTB and VDD or GND is less than 3 kΩ. A short is also detected if the impedance between BOTH

OUTA and OUTB and either VDD or GND is less than 6 kΩ. Under either of these conditions, the amplifier

outputs are disabled and FAULT is driven low. No short is detected if the impedance between either output and

VDD or GND is greater than 7.5 kΩ. Likewise, no short is detected if the impedance between BOTH outputs and

VDD or GND is greater than 15 kΩ.

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