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

Equation 10

L = VIN − VOUT × VOUT

fsw × ∆IL

VIN

PM6685

where fsw is the switching frequency, VIN is the input voltage, VOUT is the output voltage

and ∆IL is the selected inductor ripple current.

In order to prevent overtemperature working conditions, inductor must be able to provide an

RMS current greater than the maximum RMS inductor current ILRMS:

Equation 11

ILRMS =

(ILOAD (max))2

+

(∆IL (max))2

12

Where ∆IL(max) is the maximum ripple current:

Equation 12

∆IL (max)

=

VINmax

fsw

− VOUT

×L

×

VOUT

VINmax

If hard saturation inductors are used, the inductor saturation current should be much greater

than the maximum inductor peak current Ipeak:

Equation 13

Ipeak

=

ILOAD (max)

+

∆IL (max)

2

Using soft saturation inductors it’s possible to choose inductors with saturation current limit

nearly to Ipeak.

Below there is a list of some inductor manufacturers.

Table 11. Inductor manufacturer

Manufacturer

Series Inductor value (uH) RMS current (A) Saturation current (A)

COILCRAFT SER1360

4 to 8

6 to 8.6

7 to 12

COILCRAFT

MLC

2.2 to 4.5

13.6 to 8.8

11.5 to 17

TDK

RLF12560

2.7 to 10

7.5 to 11.5

7.5 to 14.4

34/52

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