Datasheet

MAX13335E/MAX13336E
Dual Automotive Differential Audio Receivers
with I
2
C Control and Diagnostics
11
Detailed Description
The MAX13335E/MAX13336E are designed to operate
with the MAX13325/MAX13326 dual automotive audio
line drivers to form a complete differential audio link
in automotive systems. In addition, the MAX13335E/
MAX13336E can operate as an auxiliary input audio
amplifier with jack sense function.
Signal Path
The devices can be configured to operate with quasi-dif-
ferential (up to 3.5V
RMS
) and fully differential (up to 7V
RMS
)
input signals. Both input channels feature high 80dB CMRR
(typ). An integrated programmable gain amplifier with zero-
crossing detection controlled through the I
2
C interface pro-
vides adjustable gain from -14dB to +16dB (MAX13335E)
or -22dB to +8dB (MAX13336E) in +2dB increments. Zero-
crossing detection can be enabled to limit the zip noise
during a gain transition by delaying the gain change until a
zero-crossing event occurs on the input signal.
Interrupt Output
The devices can monitor the inputs for the presence of
audio, clip detection, and change-of-state in the jack sense.
An active-low, open-drain interrupt request output can be
configured through the I
2
C interface to report the presence
of audio, clip detection, and change-of-state in the jack
sense. The internal status register also latches the status
change of those parameters until an I
2
C read is performed.
Thermal Shutdown
Thermal shutdown protects the device when the junction
temperature exceeds +150NC (typ). The device resumes
operation when the junction temperature drops below the
thermal shutdown hysteresis of 15NC (typ). The internal
status register latches the status change of the TSD bit
until an I
2
C read is performed.
Diagnostics
The devices feature four similar diagnostic I/O ports.
When configured correctly, they are capable of per-
forming jack sense detection, short-to-ground, short-to-
battery, open-load, and shorts between channels. Each
diagnostic I/O port contains a programmable current
source, a voltage sense, and a diode to ground.
The principle behind the diagnosis is simply forcing a
current into the load attached to the I/O port and sensing
the voltage to check if it is greater or smaller than the
two predefined low/high thresholds. These can be easily
accessed by a microcontroller through the I
2
C interface.
The procedure usually starts with stepping up the current
source from the minimum to maximum range.
1) If the sensed voltage is consistently below the low
threshold, a short-to-ground event is determined.
2) However, if the sensed voltage is consistently above
the high threshold, there is a possibility of either a
short-to-battery or an open-load event. In order to dif-
ferentiate between them, the I/O port should be tested
again with a voltage-sense-only configuration (i.e.,
with the current source switched off). If the sensed
voltage remains above the high threshold, a short-to-
battery event has occurred. Otherwise, an open-load
event is detected.
3) In some current source range, if the sensed voltage
is between the high and low thresholds, this could
indicate that the load is present.
A valid readout of the status might require some amount
of delays (to be inserted by the microcontroller) due to
the settling time needed to charge/discharge any exter-
nal capacitive load on the I/O port.
The diode is useful in the case of sensing an uncon-
nected load or short between channels. Here, one end
of the load can be forced to ground by the diode and
the usual procedure described above can be applied to
detect various events. It is, however, advisable to test the
I/O port for a short-to-battery condition prior to turning on
the diode as it could risk damaging the device.
Figure 1. Diagnostic I/O Port
V
IDH
D_
DH_
DL_
R
D_
V
IDL
40µA TO
705µA
I
2
C INTERFACE