TDA8931 Datasheet, PDF (18/31 Pages) NXP Semiconductors – Power comparator 1 X 20 W

Philips Semiconductors
TDA8931
Power comparator 1 × 20 W
14.2 Output current limiting
The output current is limited by the OCP with a threshold level of 3.3 A (minimum). During
normal operation the output current should not exceed this threshold level, otherwise the
output signal is distorted. The peak output current should stay below 3.3 A and can be
estimated using the following equation:
I_O ≤ ₂-----_×-----₍--_R----_D----_S---_o--_n----₊-----_R---^V-_L---^P-₊-----_R----_c--_o---_i-_l---₊-----_R----_E---_S---_R---₎ ≤ 3.3
(4)
Where:
I_O = output current in the load in
V_P = supply voltage (V_DDP − V_SSP)
R_DSon = on-resistance power switch
R_L = load impedance
R_coil = series resistance output coil
R_ESR = ESR of the single-ended capacitor
Example: With a 4 Ω load the OCP will be triggered below a supply voltage of 28 V. This
will result in an absolute maximum output power of P_o = 26 W at THD = 10 %.
14.3 Low pass filter considerations
For a flat frequency response (second order Butterworth filter) it is necessary to change
the LC-filter components (L1 and C14) according to the speaker impedance. Table 12
shows the required components values in case of a 4 W, 6 W or 8 W speaker impedance.
Table 12: Filter components values
Speaker impedance
(Ω)
L1 value
(µH)
4
22
6
33
8
47
C14 value
(nF)
680
470
330
14.4 Thermal behavior (printed-circuit board considerations)
The SO20 package of the TDA8931T has special thermal corner leads, significantly
increasing the power capability (reducing R_th). The corner leads (pins 1, 10, 11 and 20)
should be attached to a copper area (V_SS) on the PCB for cooling.
The typical thermal resistance R_th(j-a) of the TDA8931T is 24 K/W (free air and natural
convection) when soldered on a double sided FR4 PCB with 35 µm copper layer and
cooling area of approximately of 28 cm².
9397 750 13847
Preliminary data sheet
Rev. 01 — 14 January 2004
© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
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