TJ49300 datasheet(10/12 Pages) HTC

10 / 12 page

TJ49300

February 2011

HTC

capacitor is recommended. Larger values will help to improve ripple rejection by bypassing the input to the

regulator, further improving the integrity of the output voltage.

Feed Forward Capacitor

The TJ49300 requires a feed forward capacitor to stabilize output in case of complicated transient load condition.

It also performs a soft-start(SS) function on the output voltage. A 10nF is recommended to support its stability

support function and its higher value will increase the time of SS function.

Maximum Output Current Capability

The TJ49300 can deliver a continuous current of 3.0A over the full operating junction temperature range. However,

the output current is limited by the restriction of power dissipation which differs from packages. A heat sink

may be required depending on the maximum power dissipation and maximum ambient temperature of

application.

With respect to the applied package, the maximum output current of 3.0A may be still

undeliverable due to the restriction of the power dissipation of TJ49300. Under all possible conditions, the

junction temperature must be within the range specified under operating conditions.

The temperatures over the device are given by :

TC = TA + PD X θCA / TJ = TC + PD X θJC / TJ = TA + PD X θJA

Where TJ is the junction temperature, TC is the case temperature, TA is the ambient temperature, PD is the total

power dissipation of the device, θCA is the thermal resistance of case-to-ambient, θJC is the thermal resistance of

junction-to-case, and θJA is the thermal resistance of junction to ambient.

The total power dissipation of the device is given by:

PD = PIN – POUT = {(VIN X IIN) + (VBIAS X IBIAS)} – (VOUT X IOUT)

The maximum allowable temperature rise (TRmax) depends on the maximum ambient temperature (TAmax) of the

application, and the maximum allowable junction temperature (TJmax):

TRmax = TJmax – TAmax

The maximum allowable value for junction-to-ambient thermal resistance, θJA, can be calculated using the

formula:

θJA = TRmax / PD = (TJmax – TAmax) / PD

TJ49300 is available in SOP8-PP, TO252, and TO263 packages. The thermal resistance depends on amount of

copper area or heat sink, and on air flow.

If proper cooling solution such as heat sink, copper plane area, air flow is applied, the maximum allowable power

dissipation could be increased. However, if the ambient temperature is increased, the allowable power dissipation

would be decreased.

The θJA could be decreased with respect to the copper plane area. So, the specification of maximum power

dissipation for an application is fixed, the proper copper plane area could be estimated by following graphs.

Wider copper plane area leads lower θJA.

The maximum allowable power dissipation is also influenced by the ambient temperature. With the θJA-Copper

TJ49300 Datasheet(PDF) 10 Page - HTC Korea TAEJIN Technology Co.