MAX5019ESA datasheet(12/14 Pages) MAXIM

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Choose MOSFETs with appropriate avalanche

power ratings.

5) Choose the tertiary winding turns ratio (NT/NP) so

that the minimum input voltage provides the mini-

mum operating voltage at VDD (13V). Use the follow-

ing equation to calculate the tertiary winding turns

ratio:

where:

VDDMIN is the minimum VDD supply voltage (13V).

VDDMAX is the maximum VDD supply voltage (36V).

VIN_MIN is the minimum input supply voltage (36V).

VIN_MAX is the maximum input supply voltage (72V

in this design example).

NP is the number of turns of the primary winding.

NT is the number of turns of the tertiary winding.

Choose NT = 6.

6) Choose RSENSE according to the following equation:

where:

VILim is the current-sense comparator trip threshold

voltage (0.465V).

NS/NP is the secondary side turns ratio (5/14 in this

example).

IOUTMAX is the maximum DC output current (10A in

this example).

7) Choose the inductor value so that the peak ripple

current (LIR) in the inductor is between 10% and

20% of the maximum output current.

where VD is the output Schottky diode forward volt-

age drop (0.5V).

8) The size and ESR of the output filter capacitor deter-

mine the output ripple. Choose a capacitor with a

low ESR to yield the required ripple voltage.

Use the following equations to calculate the peak-to-

peak output ripple:

where:

VRIPPLE is the combined RMS output ripple due to

VRIPPLE,ESR, the ESR ripple, and VRIPPLE,C, the

capacitive ripple. Calculate the ESR ripple and

capacitive ripple as follows:

VRIPPLE,ESR = IRIPPLE x ESR

VRIPPLE,C = IRIPPLE/(2 x

π x 275kHz x COUT)

Layout Recommendations

All connections carrying pulsed currents must be very

short, be as wide as possible, and have a ground plane

as a return path. The inductance of these connections

must be kept to a minimum due to the high di/dt of the

currents in high-frequency switching power converters.

Current loops must be analyzed in any layout pro-

posed, and the internal area kept to a minimum to

reduce radiated EMI. Ground planes must be kept as

intact as possible.

Chip Information

TRANSISTOR COUNT: 589

PROCESS: BiCMOS

RIPPLE

RIPPLE ESR

RIPPLE C

≥ ()

()

××

=µ

5 5

1 0 198

0 4 275

401

kHz

V-

OUT

≥

()×()

××

LIR

kHz I

DMIN

OUTMAX

275

RSENSE ≤

××

=Ω

0 465

12 10

109

SENSE

ILIM

≤

××

.IOUTMAX

13 7

36 7

533

7 14

×≤

≤

≤≤

DDMIN

IN_MIN

DDMAX

IN_MAX

×≤

≤

1 +

DSMAX ≥×









144

Current-Mode PWM Controllers with Integrated

Startup Circuit

______________________________________________________________________________________

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