1A L.D.O VOLTAGE REGULATOR
LM1117
APPLICATION INFORMATION
Maximum Output Current Capability
The LM1117 can deliver a continuous current of 1A 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 1A may be still undeliverable due to the
restriction of the power dissipation of LM1117. 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
LM1117 is available in SOT223, TO252 and SOT89 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
137°C/W for SOT-223 package, over 105 °C/W for TO252 package, over 315 °C/W for SOT-89 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
Characteristic
Symbol
Rating
Unit
Thermal Resistance Junction-To-Ambient / SOT-223
Thermal Resistance Junction-To-Ambient / TO-252
Thermal Resistance Junction-To-Ambient / SOT-89
θJA-SOT-223
θJA-TO-252
θJA-SOT-89
137
105
315
°C/W
°C/W
°C/W
No heat sink / No air flow / No adjacent heat source / 0.066 inch2 copper area. (TA=25°C)
Mar. 2013 Rev. 1.22
- 12 -
HTC
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
