1A L.D.O. VOLTAGE REGULATOR
LM1117S/RS/F
Maximum Output Current Capability
The LM1117 can deliver a continuous current of 1A over the full operating junction temperature range. However, the
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 th
applied package, the maximum output current of 1A may be still undeliverable due to the restriction of the power diss
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
TJ is the junction temperature, TC is the case temperature, TA is the ambient temperature, PD is the total power dissi
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 max
allowable temperature rise (TRmax) depends on the maximum ambient temperature (TAmax) of the application
and the maximum allowable junction temperature (TJmax):
T
Rmax = TJmax – TAmax
The maximum allowable value for junction-to-ambient thermal resistance, θ JA, can be calculated using the formula:
JA = TRmax / PD
θ
LM1117 is available in SOT223, TO252 packages. The thermal resistance depends on amount of copper area or he
and on air flow. If the maximum allowable value of θJA calculated above is over 130°C/W for SO-223 package, over
for TO252 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 cop
plane is required. In summary, the absolute maximum ratings of thermal resistances are as follow:
Absolute Maximum Ratings of Thermal Resistance
Characteristic
Symbol
Max. Rating
Unit
°C/W
°C/W
°C/W
Thermal Resistance Junction-To-Ambient / SOT223
Thermal Resistance Junction-To-Ambient / TO252
Thermal Resistance Junction-To-Ambient / SOT89
θJA-SOT223
θJA-TO252
θJA-SOT89
130
93
315
No heat sink / No air flow / No adjacent heat source / 0.066 inch2 copper area
Jan. 2007 - Rev 1.0
HTC
11
HTC [ HTC KOREA TAEJIN TECHNOLOGY CO. ]
