LM5160APWPR datasheet(22/28 Pages) TI1

22 / 28 page

OUT2

OUT1

OUT2

IN(MIN)

R(diode)

IN(max)

OUT(ISO)

32 V 1.5 12 V

60 V

OUT(ISO)

OUT

0.7 V

8.47 V

1.5

LM5160A, LM5160

SNVSA03C – OCTOBER 2014 – REVISED AUGUST 2016

www.ti.com

Product Folder Links: LM5160A LM5160

Submit Documentation Feedback

8.2.2.2 Detailed Design Procedure

The Fly-Buck converter design procedure closely follows the buck converter design outlined in LM5160

Synchronous Buck (10-V to 60-V Input, 5-V Output, 1.5-A Load) . The selection of primary output voltage,

transformer turns ratio, rectifier diode, and output capacitors are covered here.

8.2.2.2.1

Selection of VOUT1 and Turns Ratio

The primary output voltage in a Fly-Buck converter must be no more than one half of the minimum input voltage.

For a minimum VIN of 18 V, the primary output voltage (VOUT) must be no higher than 9 V. To generate an

isolated output voltage of VOUT (ISO) = 12 V, a transformer turns ratio (N1:N2) of 1:1.5 is selected. Using this turns

ration, the required primary output voltage VOUT is calculated in Equation 19:

(19)

The 0.7 V subtracted from VOUT(ISO) represents the forward voltage drop of the secondary rectifier diode. Fine

tuning the primary side VOUT1 may be required to account for voltage errors due to the leakage inductance of the

transformer and the resistance of the transformer windings and the low-side FET of LM5160.

8.2.2.2.2

Secondary Rectifier Diode

The secondary rectifier diode must block the maximum input voltage multiplied by the transformer turns ratio.

The minimum diode reverse voltage VR(diode) rating is given by Equation 20:

(20)

A diode of 60 V or higher reverse voltage rating must be selected in this application. If the input voltage (VIN) has

transients above the normal operating maximum input voltage of 32 V, then the worst-case transient input

voltage must be used in the diode voltage calculation of Equation 20.

8.2.2.2.3

External Ripple Circuit

Type 3 ripple circuit is required for Fly-Buck applications. The design procedure for ripple components is identical

to that in a buck converter. See Ripple Configuration for ripple design information.

8.2.2.2.4

Output Capacitor (COUT2)

The Fly-Buck output capacitor conducts higher ripple current than a buck converter output capacitor. The

capacitive ripple for the isolated output capacitor is calculated based on the time the rectifier diode is off. During

this time the entire output current is supplied by the output capacitor. The required capacitance for a worst-case

VOUT2 (VOUT (ISO)) ripple voltage can be calculated using Equation 21 where, ΔVOUT2 is the target ripple at the

secondary output.

(21)

Equation 21 is an approximation and ignores the ripple components associated with ESR and ESL of the output

capacitor. For a ΔVOUT2 = 100 mV, Equation 21 requires COUT2 = 6.5 µF. When selecting a capacitor, consider its

DC bias to ensure sufficient capacitance over the output voltage.

LM5160APWPR Datasheet(PDF) 22 Page - Texas Instruments

LM5160APWPR Datasheet(HTML) 22 Page - Texas Instruments

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28

Datasheet Download

Link URL