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SSTIMER FUNCTIONALITY

THERMAL INFORMATION

TAS5102

TAS5103

SLLS801A – JUNE 2008 – REVISED JUNE 2008 .............................................................................................................................................................. www.ti.com

and heat can be continually removed from the IC.

Because of the efficiency of the TAS5102, heatsinks

The SSTIMER pin uses a capacitor connected

can be used which are much smaller than those

between this pin and ground to control the output

required

for

linear

amplifiers

equivalent

duty cycle when a transition occurs on the RESET

performance.

pin. The capacitor on the SSTIMER pin is slowly

charged through an internal current source, and the

RθJA is a system thermal resistance from junction to

charge time determines the rate at which the output

ambient air. As such, it is a system parameter with

transitions from a near zero duty cycle to the duty

roughly the following components: RθJC (the thermal

cycle that is present on the inputs. This allows for a

resistance from junction to case, or in this instance

smooth transition with no audible pop or click noises

the metal pad), thermal grease thermal resistance,

when the RESET pin transitions from high-to-low or

and heatsink thermal resistance. RθJC has been

low-to-high.

provided in the Device Information section. The

thermal grease thermal resistance can be calculated

For a high-to-low transition of the RESET pin

from the exposed pad area and the thermal grease

(shutdown case), it is important for the modulator to

manufacturer's area thermal resistance (expressed in

remain switching for a period of at least 10 ms (if

°C-in2/W).

The

area

thermal

resistance

the

using a 2.2 nF capacitor). Larger capacitors will

example thermal grease with a 0.001-inch thick layer

increase the start-up/shutdown time, while capacitors

is about 0.054 °C-in2/W. The approximate exposed

smaller

than

2.2

will

decrease

the

pad area is 0.01164 in2. Dividing the example thermal

start-up/shutdown time. The inputs MUST remain

grease area resistance by the area of the pad gives

switching on the shutdown transition to allow the

the actual resistance through the thermal grease , 3.3

outputs to slowly ramp down the duty cycle to near

°C/W.

zero before completely shutting off. The SSTIMER

pin should be left floating for BD modulation and also

Heatsink thermal resistance is generally predicted by

for SE (single-ended) mode.

the heatsink vendor, modeled using a continuous flow

dynamics (CFD) model, or measured.

Thus for a single IC, the system RθJA= RθJC + thermal

grease resistance + heatsink resistance.

The thermally augmented package provided with the

TAS5102 is designed to be interfaced directly to a

Thermal information for the TAS5103 Pad Down

heatsink using a thermal interface compound (for

design can be found in TI document SLMA002B.

example, Wakefield Engineering type 126 thermal

PowerPAD Thermally Enhanced Package Application

grease.) The heatsink then absorbs heat from the IC

Report . Additional material regarding thermal metrics

and couples it to the local air. If the heatsink is

can be found in TI document SPRA953A, IC Package

carefully designed, this process can reach equilibrium

Thermal Metrics (Rev. A).

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