MAX17632 datasheet(21/25 Pages) MAXIM

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Calculate resistor R7 from the FB pin to SGND as follows:

(

)

OUT

R6 0.9

R7 =

- 0.9

R7 is in kΩ.

Power Dissipation

At a particular operating condition, the power losses that

lead to temperature rise of the part are estimated as follows:

(

)

LOSS

OUT

DCR

= P

-1 - I



××





OUT

= V

x I

where:

POUT = Output power

η = Efficiency of the converter

RDCR = DC resistance of the inductor (see the Typical

Operating Characteristics for more information on effi-

ciency at typical operating conditions).

For a typical multilayer board, the thermal performance

metrics for the package are given below:

θJA = 38°C/W

θJC = 10°C/W

The junction temperature of the device can be estimated

at any given maximum ambient temperature (TA(MAX))

from the following equation:

(

)

J(MAX)

A(MAX)

LOSS

= T

θ×

If the application has a thermal-management system that

ensures that the exposed pad of the device is maintained

at a given temperature (TEP(MAX)) by using proper heat

sinks, then the junction temperature of the device can be

estimated at any given maximum ambient temperature as:

(

)

J(MAX)

EP(MAX)

LOSS

= T

θ×

Note: Junction temperatures greater than +125°C

degrades operating lifetimes.

PCB Layout Guidelines

All connections carrying pulsed currents must be very

short and as wide as possible. The inductance of these

connections must be kept to an absolute minimum due to

the high di/dt of the currents. Since inductance of a cur-

rent-carrying loop is proportional to the area enclosed by

the loop, if the loop area is made very small, inductance

is reduced. Additionally, small-current loop areas reduce

radiated EMI.

A ceramic input filter capacitor should be placed close

to the VIN pins of the IC. This eliminates as much trace

inductance effects as possible and gives the IC a cleaner

voltage supply. A bypass capacitor for the VCC pin also

should be placed close to the pin to reduce effects of trace

impedance.

When routing the circuitry around the IC, the analog small

signal ground and the power ground for switching cur-

rents must be kept separate. They should be connected

together at a point where switching activity is minimum.

This helps keep the analog ground quiet. The ground

plane should be kept continuous (unbroken) as far as

possible. No trace carrying high switching current should

be placed directly over any ground plane discontinuity.

PCB layout also affects the thermal performance of the

design. A number of thermal throughputs that connect to a

large ground plane should be provided under the exposed

pad of the part, for efficient heat dissipation.

For a sample layout that ensures first pass success, refer

to the MAX17632 evaluation kit layout available at www.

maximintegrated.com.

Figure 2. Setting the Output Voltage

VOUT

SGND

www.maximintegrated.com

Maxim Integrated │ 21

MAX17632

4.5V to 36V, 2A, High-Efficiency,

Synchronous Step-Down DC-DC Converter

MAX17632 Datasheet(PDF) 21 Page - Maxim Integrated Products

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