MAX5083 datasheet(14/18 Pages) MAXIM

14 / 18 page

1.5A, 40V, MAXPower Step-Down

DC-DC Converters

______________________________________________________________________________________

Since R3 >> R6, R3 + R6 can be approximated as R3.

R3 is then calculated as:

fP3 is set at 5xfC. Therefore, C8 is calculated as:

Power Dissipation

The MAX5082/MAX5083 is available in a thermally

enhanced package and can dissipate up to 2.7W at TA =

+70°C. When the die temperature reaches +160°C, the

part shuts down and is allowed to cool. After the part

cools by 20°C, the device restarts with a soft-start.

The power dissipated in the device is the sum of the

power dissipated from supply current (PQ), transition

losses due to switching the internal power MOSFET

(PSW), and the power dissipated due to the RMS cur-

rent through the internal power MOSFET (PMOSFET).

The total power dissipated in the package must be lim-

ited such that the junction temperature does not

exceed its absolute maximum rating of +150°C at maxi-

mum ambient temperature. Calculate the power lost in

the MAX5082/MAX5083 using the following equations:

The power loss through the switch:

PMOSFET = IRMS_MOSFET2 x RON

RON is the on-resistance of the internal power MOSFET

(see the Electrical Characteristics).

The power loss due to switching the internal MOSFET:

where tR and tF are the rise and fall times of the internal

power MOSFET measured at LX.

The power loss due to the switching supply current

(ISW):

PQ = VIN x ISW

The total power dissipated in the device will be:

PTOTAL = PMOSFET + PSW + PQ

Chip Information

TRANSISTOR COUNT: 4300

PROCESS: BiCMOS/DMOS

()

××

OUT

()

MOSFET

RMS MOSFET

OUT

=×

[]×

=−

−

∆

()

××

−

≈

××

π LC

GAIN

(dB)

VOUT

REF

COMP

FREQUENCY

CLOSED-LOOP

GAIN

fZ1 fZ2

fP2

fP3

Figure 4. Error Amplifier Compensation Circuit (Closed-Loop

and Error Amplifier Gain Plot) for Higher ESR Output Capacitors

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