LM37101 datasheet(10/11 Pages) HTC

10 / 11 page

1A Low-Voltage Low-Dropout Regulator

LM37101/37102

Nov. 2011 – R1.1

- 10

HTC

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 LM37101/2. 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

LM37101/2 is available in SOP-8 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 130°C/W for SOP-8

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 / SOP-8

θJA-SOP-8

130

°C/W

Thermal Resistance Junction-To-Ambient / TO-252

θJA-TO-252

°C/W

No heat sink / No air flow / No adjacent heat source / 20 mm

2 copper area. (T

A=25°C)

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