1A L.D.O VOLTAGE REGULATOR(Automotive Grade)
APPLICATION INFORMATION
LM1117Q
Maximum Output Current Capability
The LM1117Q 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 LM1117Q. 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
LM1117Q is available in SOT223 package. 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, 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
θJA-SOT-223
137
°C/W
No heat sink / No air flow / No adjacent heat source / 0.066 inch2 copper area. (TA=25°C)
Jul. 2011 Rev. 1.0
- 11 -
HTC
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
