SN6501DBVT datasheet(18/29 Pages) TI1

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1 F

MBR0520L

SN6501

TP1

0.1µF

GND

10 µF

0.1 µF

VIN

10µF

MBR0520L

10 µF

SN6501

LDO

TP 1

TP 2

VOUT

0.1µF

Vcc

GND

OUT

GND

min

0.2V + 0.2V + 5.175 V

= 1.031

= 2

3.234 V

3 Ω

150 mA

F-max

DO-max

O-max

min

IN-min

DS-max

D-max

+ V

= 1.031

SN6501

SLLSEA0E – FEBRUARY 2012 – REVISED JANUARY 2013

www.ti.com

Then calculating the available minimum primary voltage, VP-min, involves subtracting the maximum possible drain-

source voltage of the SN6501, VDS-max, from the minimum converter input voltage VIN-min:

VP-min = VIN-min – VDS-max

(5)

VDS-max however, is the product of the maximum RDS(on) and ID values for a given supply specified in the SN6501

data sheet:

VDS-max = RDS-max × IDmax

(6)

Then inserting Equation 6 into Equation 5 yields:

VP-min = VIN-min - RDS-max x IDmax

(7)

and inserting Equation 7 and Equation 4 into Equation 3 provides the minimum turns ration with:

(8)

Example:

For a 3.3 VIN to 5 VOUT converter using the rectifier diode MBR0520L and the 5 V LDO TPS76350, the data

sheet values taken for a load current of 100 mA and a maximum temperature of 85°C are VF-max = 0.2 V,

VDO-max = 0.2 V, and VO-max = 5.175 V.

Then assuming that the converter input voltage is taken from a 3.3 V controller supply with a maximum ±2%

accuracy makes VIN-min = 3.234 V. Finally the maximum values for drain-source resistance and drain current at

3.3 V are taken from the SN6501 data sheet with RDS-max = 3 Ω and ID-max = 150 mA.

Inserting the values above into Equation 8 yields a minimum turns ratio of:

(9)

Most commercially available transformers for 3-to-5 V push-pull converters offer turns ratios between 2.0 and 2.3

with a common tolerance of ±3%.

Recommended Transformers

Depending on the application, use the minimum configuration in Figure 51 or standard configuration in Figure 52.

Figure 51. Unregulated Output for Low-Current

Figure 52. Regulated Output for Stable Supplies

Loads with Wide Supply Range

and High Current Loads

The Wurth Electronics Midcom isolation transformers in Table 2 are optimized designs for the SN6501, providing

high efficiency and small form factor at low-cost.

The 1:1.1 and 1:1.7 turns-ratios are designed for logic applications with wide supply rails and low load currents.

These applications operate without LDO, thus achieving further cost-reduction.

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