tda2500 Tripath Technology Inc., tda2500 Datasheet - Page 19

• Manufacturer Part Number: tda2500
• Description: Stereo Class-t Digital Audio Amplifier Driver Using Digital Power Processing Dpp
• Manufacturer: Tripath Technology Inc.

T r i p a t h T e c h n o l o g y , I n c . - T e c h n i c a l I n f o r m a t i o n
TDA2500. Thus, a current limit into a “short” will produce a peak current level roughly twice that of an
over-current into a 4: (or higher) load. The calculation above is for an over current condition (driving a
4:resistor for example). Thus, the peak current into a short will be roughly double of the calculation
above.
AUXILLARY OVER-CURRENT DETECTION CIRCUITS
As noted in the previous section, the current trip point into a short is roughly twice that of (requires very
little output voltage swing) a load which produces a over current fault near the maximum voltage swing of
the amplifier. In most cases, MOSFETs can withstand 3-4 times the rated continuous current for short
durations (less than 100uS). Thus, for most situations this additional current does not cause any damage
to the output MOSFETs and / or the TDA2500.
But in some cases, it may be desirable to have a more constant current trip point, i.e. a current trip that is
constant across all ranges of duty cycle and output switching frequency. The RB-TDA2500 reference
board shows one such circuit. This circuit augments the internal half-wave circuit to create a full wave
circuit that has little or no duty cycle effect.
Please refer to the RB-TDA2500 document at
www.tripath.com
for circuit details.
Instead, it may be desirable to create an entirely separate current detection circuit. Unlike previous hybrid
modules from Tripath such as TA0104A and TA0105A, the internal comparators used in the detection
process are directly connected to the OCR1 and OCR2 pins. As shown in the Electrical Characteristics
table, the threshold for the comparator is 0.97V typically.
Also, there is about 3uS of time-based
deglitching. Thus, the comparator input has to be above 0.97V for 3uS to create an over-current fault.
This comparator input can be used to feed in a voltage from an external detection circuit. In this case, the
detection circuit on the TDA2500 can be disabled by individually shorting each of the four OCSx pin pairs
directly at the TDA2500.
OVER- VOLTA GE AND UND ER- VOLTA GE PROTECTION
The TDA2500 senses the power rails through the VPP and VNN pins on the module. These voltages are
converted to currents by internal (and typically external, also) resistor networks connected to VLOW and
VHIGH. The over-voltage and under-voltage limits are determined by the internal bias currents, the values
of the resistors in the networks, along with process variations. If the supply voltage falls outside the upper
and lower limits determined by the resistor networks, the TDA2500 shuts off the output stages of the
amplifiers. The removal of the over-voltage or under-voltage condition returns the TDA2500 to normal
operation. Please note that trip points specified in the Electrical Characteristics table are at 25qC and
may change over temperature.
Once the supply comes back into the supply voltage operating range (as defined by the power supply
sense resistors), the TDA2500 will automatically be un-muted and resume amplification. There is a
hysteresis range on both the VPP and VNN supplies. If the amplifier is powered up in the hysteresis
band, the TDA2500 will be muted. Thus, the usable supply range is the difference between the over-
voltage restart and under-voltage restart points for both the VPP and VNN supplies. It should be noted
that there is a timer of approximately 200mS with respect to the over and under voltage sensing circuit.
Thus, the supply voltage must be outside of the user defined supply range for greater than 200mS for the
TDA2500 to be muted.
The over-voltage and under-voltage resistor values were chosen for the maximum supply range possible
based on the internal hybrid components in conjunction with internal bias current settings. In most
applications using the TDA2500, external resistors will be used to lower the supply range for VPP and
VNN. The delta between each of the trip points is a fixed ratio and not externally controllable. The current
flowing into VHIGH controls the supply range for VPP while the current flowing out of VLOW controls the
supply range for VNN.
Figure 4 shows the proper connection for the Over / Under voltage sense circuit for both the VPPSENSE
and VNNSENSE pins.
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TDA2500 – KL/ Rev. 0.9/05.05