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FR1117P/S/D/F-AD ~ FR1117P/S/D/F-5.0

Revision No : 7

APPLICATION INFORMATION

Maximum Output Current Capability

The FR1117 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 FR1117. 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 = (V N 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 resistan

ce, θJA, can be calculated using the

formula:

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

FR1117 is available in SOT-223, TO-252 and SOT-89 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 TO-252 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

ti

n

U

g

n

it

a

R

l

o

b

m

y

S

c

it

s

ir

e

t

c

a

r

a

h

C

Thermal Resistance Junction-To-Ambient / SOT-223

θJA-SOT-223

137

°C/W

Thermal Resistance Junction-To-Ambient / TO-252

θJA-TO-252

105

°C/W

Thermal Resistance Junction-To-Ambient / SOT-89

θJA-SOT-89

315

°C/W

No heat sink / No air flow / No adjacent heat source / 0.066 inch

2 copper area. (T

A=25°C)