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Error Reporting Over Current (OC) Protection With Current
Device Protection System
TAS5261
SLES188 AUGUST 2006
Limiting and Overload Detection
The SD and OTW pins are both active-low,
open-drain outputs. Their function is for The device has independent, fast-reacting current
protection-mode signaling to a PWM controller or detectors with programmable trip threshold (OC
other system-control device. Any fault resulting in threshold) on all high-side and low-side power-stage
device shutdown is signaled by the SD pin going low. FETs. See Table 3 for OC-adjust resistor values. The
Likewise, OTW goes low when the device junction detector outputs are closely monitored by two
temperature exceeds 115 ° C. (see Table 2 ). protection systems. The first protection system
controls the power stage in order to prevent the
Table 2. Error Reporting output current from further increasing. For instance, it
performs a current-limiting function rather than
SD OTW DESCRIPTION
prematurely shutting down during combinations of
Over Temperature (OTE) or Over
high-level music transients and extreme speaker
0 0
Load (OLP) or Under Voltage (UVP)
load impedance drops. If the high-current situation
Over Load (OLP), PWM Activity
persists, i.e., the power stage is being overloaded, a
0 1
Dectector, or Under Voltage (UVP)
second protection system triggers a latching
Over Temperature Warning. Junction
shutdown, resulting in the power stage being set in
1 0
temperature higher than 125 ° C.
the high-impedance (Hi-Z) state.
Normal operation. Junction
1 1
temperature lower than 125 ° C.
Table 3. OC-Adjust Resistor Values
It should be noted that asserting RESET low forces
CURRENT BEFORE OC OCCURS
OC-ADJUST
(A)
the SD and OTW signals high, independent of faults
RESISTOR VALUES
(k )
(1)
being present. It is recommended to monitor the
MIN TYP MAX
OTW signal using the system microcontroller and
22 15 16 17
respond to an overtemperature warning signal by, for
27 12 13 14
example, turning down the volume to prevent further
47 7 8 8
heating of the device resulting in device shutdown
68 5 5 6
( OTW). To reduce external component count, an
internal pullup resistor to 3.3 V is provided on both
100 3 4 4
the SD and OTW outputs. Level compliance for 5-V
(1) Resistor tolerance is ± 5%.
logic can be obtained by adding external pullup
resistors to 5 V (see the Electrical Characteristics
For lowest-cost bill of materials in terms of
section of this data sheet for further specifications).
component selection, the OC threshold current
should be limited, considering the power output
requirement and minimum load impedance.
Higher-impedance loads require a lower OC
The TAS5261 contains advanced protection circuitry
threshold.
carefully designed to facilitate system integration and
ease of use, as well as safeguarding the device from
The demodulation filter inductor must retain a
permanent failure due to a wide range of fault
minimum of 5-H inductance at twice the selected OC
conditions, such as short circuit, overload, and
threshold current.
undervoltage. The TAS5261 responds to a fault by
Most inductors have decreasing inductance with
immediately setting the power stage in a
increasing temperature and increasing current
high-impedance state (Hi-Z) and asserting the SD
(saturation). To some degree, an increase in
pin low. In situations other than overload, the device
temperature naturally occurs when operating at high
automatically recovers when the fault condition has
output currents, due to inductor core losses and the
been removed (e.g., the voltage supply has
dc resistance of the inductor copper winding. A
increased). For highest possible reliability, recovering
thorough analysis of inductor saturation and thermal
from an overload fault requires external reset of the
properties is strongly recommended.
device no sooner than 1 s after the shutdown (see
the Device Reset section of this data sheet).
Setting the OC threshold too low might cause issues,
such as lack of enough output power and/or
unexpected shutdowns due to sensitive overload
detection.
In general, it is recommended to follow closely the
external component selection and PCB layout as
given in the Application Information section of this
data sheet.
17
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