SN6501DBVT datasheet(15/26 Pages) TI1

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F-max

DO-max

O-max

min

IN-min

DS-max

D-max

+ V

= 1.031

min

0.2V + 0.2V + 5.175 V

= 1.031

= 2

3.234 V

3 Ω

150 mA

OUT = 2n·VIN

VOUT+ = n·VIN

VOUT- = n·VIN

VIN

VOUT+ = 2n·VIN

VOUT- = 2n·VIN

VIN

OUT = 4n·VIN

SN6501

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SLLSEA0C – FEBRUARY 2012 – REVISED MARCH 2012

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%.

HIGHER OUTPUT VOLTAGE DESIGNS

The SN6501 can drive push-pull converters that provide high output voltages of up to 30 V, or bipolar outputs of

up to ±15 V. Using commercially available center-tapped transformers, with their rather low turns ratios of 0.8 to

5, requires different rectifier topologies to achieve high output voltages. Figure 36 to Figure 39 show some of

these topologies together with their respective open-circuit output voltages.

Figure 36. Bridge Rectifier with Center-Tapped

Figure 37. Bridge Rectifier Without Center-Tapped

Secondary Enables Bipolar Outputs

Secondary Performs Voltage Doubling

Figure 38. Half-wave Rectifier Without Center-

Figure 39. Half-wave Rectifier Without Centered

tapped Secondary Performs Voltage Doubling,

Ground and Center-tapped Secondary Performs

Centered Ground provides Bipolar Outputs

Voltage Doubling Twice, Hence Quadrupling VIN

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