PM6685TR View Datasheet(PDF) - STMicroelectronics

Part Name

Description

MFG CO.

PM6685TR

Dual step-down main supply controller with auxilary voltages for notebook system power

STMicroelectronics 

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Monitoring and protections

PM6685

Table 16. Dual MOSFET manufacturer

Manufacturer

Type

RDSon (mΩ) Gate charge (nC)

ST

STS8DNH3LL

25

10

ST

STS4DNF60L

65

32

Rated reverse

voltage (V)

30

60

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 (0.3V). 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.

Table 17. Schottky diode manufacturer

Manufacturer

Series

Forward voltage

(V)

ST

STPS1L30M

0.34

ST

STPS1L20M

0.37

Rated reverse

voltage (V)

30

20

Reverse current

(uA)

0.00039

0.000075

8.11

Closing the integrator loop

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

is higher than approximately 30mV, the feedback network (Figure 36) is usually enough to

keep the loop stable.

Figure 36. Circuitry for output ripple compensation

COMP PIN

VOLTAGE

∆V

Vr

t

OUTPUT VOLTAGE

∆V

t

L

COMP

CFILT

CINT

RINT

VCINT

OUT

I=gm(V1-Vr)

Vr

+

gm

+

Vr V1

RFb1

- PWM

Comparator

RFb2

ROUT

D

COUT

38/52

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