MAX8862R 查看數據表（PDF） - Maxim Integrated

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MAX8862R

Low-Cost, Low-Dropout, Dual Linear Regulator

Maxim Integrated 

Low-Cost, Low-Dropout, Dual Linear Regulator

100

80

60

40

20

0

0 5 10 15 20 25 30 35

PC-BOARD COPPER FOIL AREA (Cm2)

Figure 3. Typical Copper Thermal Resistance vs. Copper

Ground Pad Area

400

MAXIMUM CURRENT

350

(L)

300

(T)

250 (R)

(R)

200

(T) (L)

MAXIMUM

150

SUPPLY

VOLTAGE

100

OPERATING REGION AT

50

TA = +25°C, TJ = +125°C

0

2 3 4 5 6 7 8 9 10 11 12

SUPPLY VOLTAGE (V)

Figure 4. Safe Operating Regions: Main and Secondary

Regulators Maximum Output Current vs. Supply Voltage

__________Applications Information

Power Dissipation and Operating Region

The MAX8862’s maximum power dissipation depends

on the thermal resistance of the case and circuit board,

the temperature difference between the die junction

and ambient air, and the rate of air flow.

The GND pins of the MAX8862 SO package perform

the dual function of providing an electrical connection

to ground and channeling heat away. Connect all GND

pins to ground using a large pad or ground plane.

Where this is impossible, place a copper plane on an

adjacent layer. For a given power dissipation, the pad

should exceed the associated dimensions in Figure 3.

This figure shows a typical thermal resistance for a

35µm-thick copper foil as a function of its area1.

The power dissipation across the device is given by:

P = IOUT1 (VIN1 - VOUT1) + IOUT2 (VIN2 - VOUT2).

The resulting power dissipation is as follows:

P = (TJ - TA) / (θJB + θBA)

where (TJ - TA) is the temperature difference between

the MAX8862 die junction and the surrounding air, θJB

(or θJC) is the thermal resistance of the package, and

θBA is the thermal resistance through the printed circuit

board, copper traces, and other materials to the sur-

rounding air. The MAX8862’s narrow SO package has a

thermal resistance of θJB = +50°C/W.

The MAX8862 regulators deliver the rated output cur-

rents and operate with input voltages up to 11.5V, but

not simultaneously. High output currents can only be

sustained when input-output differential voltages are

small, as shown in Figure 4.

Capacitor Selection and

Regulator Stability

Filter capacitors are required at the MAX8862’s inputs

and outputs. 1µF ceramic capacitors are required at

the inputs. The minimum output capacitance required

for stability is 3.3µF for OUT1 and 2.2µF for OUT2. The

capacitor values depend primarily on the desired

power-up time and load-transient response. Load-

transient response is improved by using larger capaci-

tor values. Input and output filter capacitors should be

soldered directly to pins to minimize lead inductance of

PC board traces.

The output capacitor’s equivalent series resistance

(ESR) affects stability and output noise. Surface-mount

ceramic capacitors have a very low ESR and are avail-

able up to 10µF. Otherwise, other low-ESR (<0.5Ω)

capacitors should be used. If the selected capacitor’s

ESR is higher than the recommended value, the capac-

itor value should be increased proportionally to main-

tain minimum output noise under all input voltage and

output load conditions. Paralleling two or more capaci-

tors also results in lower ESR.

1This graph was generated by Mr. Kieran O’Malley of Cherry Semiconductor Corp. and was published in the October 26, 1995, issue

of EDN magazine.

10 ______________________________________________________________________________________

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