TS4994 datasheet(25/31 Pages) STMICROELECTRONICS

25 / 31 page

Application Information

TS4994

25/31

The maximum die temperature allowable for the TS4994 is 125°C. However, in case of overheating, a

thermal shutdown set to 150°C, puts the TS4994 in standby until the temperature of the die is reduced by

about 5°C.

To calculate the maximum ambient temperature TAMB allowable, we need to know:

l Power supply Voltage value, Vcc

l Load resistor value, RL

l The package type, RTHJA

Example: Vcc=5V, RL=8

Ω, RTHJAFlip-Chip=100°C/W (100mm2 copper heatsink).

We calculate Pdissmax = 633mW.

With

TAMB = 125-100x0.633=61.7°C

4.7 Decoupling of the circuit

Two capacitors are needed to correctly bypass the TS4994. A power supply bypass capacitor CS and a

bias voltage bypass capacitor CB.

CS has particular influence on the THD+N in the high frequency region (above 7kHz) and an indirect

influence on power supply disturbances. With a value for CS of 1µF, you can expect similar THD+N

performances to those shown in the datasheet.

In the high frequency region, if CS is lower than 1µF, it increases THD+N and disturbances on the power

supply rail are less filtered.

On the other hand, if CS is higher than 1µF, those disturbances on the power supply rail are more filtered.

Cb has an influence on THD+N at lower frequencies, but its function is critical to the final result of PSRR

(with input grounded and in the lower frequency region).

4.8 Wake-up Time: TWU

When the standby is released to put the device ON, the bypass capacitor Cb will not be charged

immediately. As Cb is directly linked to the bias of the amplifier, the bias will not work properly until the Cb

voltage is correct. The time to reach this voltage is called the wake-up time or TWU and is specified in the

tables found in Electrical Characteristics on page 4, with Cb=1µF. During the wake-up time phase, the

TS4994 gain is close to zero. After the wake-up time period, the gain is released and set to its nominal

value.

If Cb has a value other than 1µF, please refer to the graph in Figure 69 on page 18 to establish the wake-

up time value.

4.9 Shutdown time

When the standby command is set, the time required to put the two output stages in high impedance and

the internal circuitry in shutdown mode is a few microseconds.

Note:

In shutdown mode, Bypass pin and Vin+, Vin- pins are short-circuited to ground by internal switches. This allows

a quick discharge of Cb and Cin capacitors.

)

(

RTH

125

diss

AMB

−

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