PM6681ATR datasheet(34/47 Pages) STMICROELECTRONICS

34 / 47 page

Design guidelines

PM6681A

34/47

Dual N-channel MOSFETs can be used in applications with a maximum output current of

about 3 A. Below there is a list of some MOSFET manufacturers.

A rectifier across the low side MOSFET is recommended. The rectifier works as a voltage

clamp across the synchronous rectifier and reduces the negative inductor swing during the

dead time between turning the high-side MOSFET off and the synchronous rectifier on. It

can increase the efficiency of the switching section, since it reduces the low side switch

losses. A Schottky diode is suitable for its low forward voltage drop (0.3 V). The diode

reverse voltage must be greater than the maximum input voltage VINmax. A minimum

recovery reverse charge is preferable. Below there is a list of some Schottky diode

manufacturers.

9.6

Closing the integrator loop

The design of external feedback network depends on the output voltage ripple. If the ripple

is higher than approximately 30 mV, the feedback network (Figure 39) is usually enough to

keep the loop stable.

Table 15.

Low side MOSFET manufacturer

Manufacturer

Type

RDS(on) (mΩ)

Rated reverse voltage (V)

STS17NF3LL

5.5

0.047

STS25NH3LL

3.5

0.011

Table 16.

Dual MOSFET manufacturer

Manufacturer

Type

RDS(on) (mΩ) Gate charge (nC) Rated reverse voltage (V)

STS8DNH3LL

STS4DNF60L

Table 17.

Schottky diode manufacturer

Manufacturer

Series

Forward voltage

(V)

Rated reverse voltage

(V)

Reverse current

(uA)

STPS1L30M

0.34

0.00039

STPS1L20M

0.37

0.000075

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