Thermal-Overload Protection

Thermal-overload protection limits total power dissipa-

tion in the MAX1658/MAX1659. When the junction tem-

deactivates, allowing the IC to cool. Once it has cooled

by 10°C, the control logic will enable operation. Under

thermal overload, the output of the device will pulse as

the die heats up and then cools to operational levels.

Prolonged operation under these conditions is not rec-

ommended.

Operating Region and Power Dissipation

Maximum power dissipation of the MAX1658/MAX1659

depends on the thermal resistance of the package and

circuit board, the temperature difference between the

die and ambient air, and the rate of air flow. The power

maximum power dissipation is:

MAX1658/MAX1659 die junction and the surrounding

air,

board, copper traces, and other materials to the

surrounding air. The 8-pin SO package for the

MAX1658/MAX1659 features a special lead frame with

a lower thermal resistance and higher allowable power

dissipation than a standard SO-8. The thermal resis-

tance of this package is

The IN pins of the MAX1658/MAX1659 package per-

form the dual function of providing an electrical con-

nection to IN and channeling heat away. Connect all IN

pins to the input voltage using a large pad or power

plane on the surface. Where this is impossible, connect

to a copper plane on an adjacent layer. The pad should

meet the dimensions specified in Figure 4.

Figure 4 assumes the IC is soldered directly to the pad,

has a +125°C maximum junction temperature and a

+25°C ambient air temperature, and has no other heat

sources. Use larger pad sizes for lower junction tem-

peratures, higher ambient temperatures, or conditions

where the IC is not soldered directly to a heat-sinking

IN pad.

The MAX1658/MAX1659 can regulate currents up to

350mA and operate with input voltages up to 16.5V, but

not simultaneously. High output currents can only be

sustained when input-output differential voltage is low,

as shown in the following equation. Maximum power

dissipation depends on packaging, board layout, tem-

perature, and air flow. The maximum output current is:

Figure 4.

Reverse Battery Protection

The MAX1658/MAX1659 feature reverse battery protec-

tion. Under normal operation, a P-channel MOSFET

connects the substrate of the device to IN. When the

input voltage falls below ground (implying reverse bat-

tery conditions), the P-channel switch turns off and dis-

connects the substrate from IN, disabling the device.

The maximum reverse battery voltage allowed is -17V.

SHDN also withstands reverse battery conditions and

can be connected directly to IN with no loss of protec-

tion.

Polarized input bypass capacitors will be damaged

under reverse battery conditions. To ensure circuit reli-

ability, use a non-polarized capacitor at the input.

The MAX1658/MAX1659 do not provide reverse current

300mV, reverse current will flow. Reverse current pro-

tection can be added by connecting a Schottky diode

in series with IN.

I

P

x

C

T

V

V

x

C

OUT MAX

MAX

A

IN

OUT

(

)

=

° −

(

)

−

(

)

°

125

100

P

T

T

MAX

J

A

JB

BA

=

−

(

)

+

(

)













θ

θ

350mA, 16.5V Input,

Low-Dropout Linear Regulators

8

_______________________________________________________________________________________

1600

1400

1200

1000

800

600

400

0.1

0.65

1

6.5

COPPER GROUND PAD AREA

SINGLE-SIDED 1oz. COPPER

Figure 4. Typical Maximum Power Dissipation vs. Ground Pad

Area