LM48100Q

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SNAS470D – OCTOBER 2008 – REVISED MARCH 2013

GENERAL AMPLIFIER FUNCTION

Bridge Configuration Explained

The LM48100Q 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 5V supply is 158mW, while the

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

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

Input 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

Table 6. Input Multiplexer Control

INPUT_1

INPUT_2

LM48100Q OUTPUT

0

0

MUTE. No input selected

1

0

IN1 ONLY

0

1

IN2 ONLY

1

1

IN1 + IN2

OUTPUT FAULT DETECTION

With a standard speaker load (6

Ω - 100Ω) connected between OUTA and OUTB, the LM48100Q can detect a

is greater than 7.5k

greater than 15k

Ω.

Output Short Circuit and Open Circuit Detection

The LM48100Q can detect whether the amplifier outputs have been shorted together or, an output open circuit

condition has occurred. An output short circuit is detected if the impedance between OUTA and OUTB is less

than 2

Ω. An open circuit is detected if the impedance between OUTA and OUTB is greater than 200Ω. Under

either of these conditions, the amplifier outputs are disabled and FAULT is driven low. The device remains in

normal operation if the impedance between OUTA and OUTB is in the range of 6

Ω to 100Ω. The output open

circuit test is only performed during the initial diagnostic sequence during power up, or when DG_ENABLE is set

to 1.

Output Over-Current Detection

The LM48100Q has two over current detection modes, a fixed current limit, and a supply dependent current limit.

Bit B1 (ILIMIT) of the Diagnostic Control Register selects the over-current detection mode. Set ILIMIT = 0 to

select a fixed current limit of 1.47A (typ). Set ILIMIT = 1 to select the supply dependent current limit mode. In

supply dependent mode, the current limit is determined by Equation 1:

(A)

(1)

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