Setting the Input Undervoltage-Lockout Level

The device offers an adjustable input undervoltage-lockout

level. Set the voltage at which the device turns on with

Connect the center node of the divider to EN/UVLO.

Choose R1 to be 3.3MΩ and then calculate R2 as follows:

×

=

INU

R1 1.215

R2

(V

-1.215)

If the EN/UVLO pin is driven from an external signal source,

a series resistance of minimum 1kΩ is recommended to be

placed between the signal source output and the EN/UVLO

pin, to reduce voltage ringing on the line.

Loop Compensation

The device is internally loop-compensated. However, if

the switching frequency is less than 500kHz, connect a

0402 capacitor C6 between the CF pin and the FB pin.

Use Table 2 to select the value of C6.

If the switching frequency is less than 200kHz, connect

an additional R-C network in parallel to the top resistor of

the feedback divider (R3). See Figure 5 to calculate the

values of the components R7, C12, and C6.

Adjusting Output Voltage

Set the output voltage with a resistive voltage-divider

connected from the positive terminal of the output

center node of the divider to the FB pin. Use the following

procedure to choose the resistive voltage-divider values:

Calculate resistor R3 from the output to the FB pin as

follows:

OUT

R3 39 V

=

×

where R3 is in kΩ.

Calculate resistor R4 from the FB pin to SGND as follows:

×

=

OUT

R3 0.9

R4

(V

- 0.9)

Power Dissipation

Ensure that the junction temperature of the device

does not exceed 125ºC under the operating conditions

specified for the power supply.

At a particular operating condition, the power losses that

lead to temperature rise of the part are estimated as

follows:

(

)

=

××

η

2

LOSS

OUT

DCR

OUT

1

P

(P

( -1)) - I

R

=

×

OUT

OUT

OUT

P

VI

inductor. (See the Typical Operating Characteristics for more

information on efficiency at typical operating conditions.)

For a multilayer board, the thermal performance metrics

for the package are given below:

θ=

°

θ= °

Figure 2. Setting the Input Undervoltage Lockout

Figure 3. Setting the Output Voltage

Table 2. C6 Capacitor Value at Various

Switching Frequencies

SWITCHING FREQUENCY RANGE (kHz)

C6 (pF)

200 to 300

2.2

300 to 400

1.2

400 to 500

0.75

SGND

R3

R4

FB

SGND

R1

R2

EN/UVLOV

MAX17543

4.5V–42V, 2.5A, High-Efficiency,

Synchronous Step-Down DC-DC Converter

with Internal Compensation

www.maximintegrated.com

Maxim Integrated │ 15