3.0A Ultra Low Dropout Linear Regulator
TJ3966
Maximum Output Current Capability
The TJ3966 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 TJ3966. 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)–(VOUT X IOUT
)
= (VIN X (IOUT+IGND)) – (VOUT X IOUT) = (VIN - VOUT) X IOUT + VIN X IGND
where IGND is the operating ground current of the device which is specified at the Electrical Characteristics.
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
TJ3966 is available in SOP8-PP, TO225, TO263 and TO220 packages. The thermal resistance depends
on amount of copper area or heat sink, and on air flow. If the maximum allowable value of θJA calculated
above is over 175°C/W for SOP8-PP package, over 105 °C/W for TO252 package, over 80 °C/W for
TO263 package, over 70 °C/W for TO220 package, no heat sink is needed since the package can
dissipate enough heat to satisfy these requirements. If the value for allowable θJA falls near or below
these limits, a heat sink or proper area of copper plane is required.
In summary, the absolute maximum ratings of thermal resistances are as follow:
Absolute Maximum Ratings of Thermal Resistance
No heat sink / No air flow / No adjacent heat source / TA = 25°C
Characteristic
Symbol
θJA-SOP8-PP
θJA-TO252
θJA-TO263
θJA-TO220
Rating
175
105
80
Unit
°C/W
°C/W
°C/W
°C/W
Thermal Resistance Junction-To-Ambient / SOP8-PP
Thermal Resistance Junction-To-Ambient / TO252
Thermal Resistance Junction-To-Ambient / TO263
Thermal Resistance Junction-To-Ambient / TO220
70
In case that there is no cooling solution and no heat sink / copper plane area for heat sink, the maximum
allowable power dissipation of each package is as follow;
Aug. 2010 - Rev. 1.7.1
- 9 -
HTC
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
