Datasheet

LM48100Q
www.ti.com 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 8Ω 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
amplifier outputs are both biased about V
DD
/2, there is no net DC voltage across the load, eliminating the DC
blocking capacitors required by single-ended, single-supply amplifiers.
Input Mixer/Multiplexer
The LM48100Q features an input mixer/multiplexer controlled through the I
2
C 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 V
IN1
and V
IN2
, and the LM48100Q outputs the result as a mono signal (Table 7).
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
Output Short to Supplies (V
DD
or GND)
With a standard speaker load (6Ω - 100Ω) connected between OUTA and OUTB, the LM48100Q can detect a
short between the outputs and either V
DD
or GND. A short is detected if the impedance between either OUTA or
OUTB and V
DD
or GND is less than 3kΩ. A short is also detected if the impedance between BOTH OUTA and
OUTB and either V
DD
or GND is less than 6kΩ. 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 V
DD
or GND
is greater than 7.5kΩ. Likewise, no short is detected if the impedance between BOTH outputs and V
DD
or GND is
greater than 15kΩ.
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 2Ω. 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 6Ω 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:
I
SHTCKT
= 0.264 x V
DD
(A) (1)
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