3.3k

5.45k

6V

(2.7V)

< 1.21V

100k

3.3k

100k

5.45k

W

W

æ

ö

æ

ö

+

ç

÷

ç

÷

W +

W

W +

W

è

ø

è

ø

(

)

IN

IN

OUT

R7

R6

V

V

V

Vref

R5

R7

R5

R6

æ

ö

æ

ö

+

-

<

ç

÷

ç

÷

+

+

è

ø

è

ø

(

) (

)

3.3V

R6

3.19k

3.19k

1.22V

=

W -

W

OUT

V

R6

(R5 | |R7) (R5 || R7)

1.22V

=

-

R5 R7

(R5 | |R7)

3.19k

R5 R7

´

=

=

+

Ω

TL1963A, TL1963A-15, TL1963A-18, TL1963A-25, TL1963A-33

SLVS719G – JUNE 2008 – REVISED JANUARY 2015

www.ti.com

The TLV3691 rail-to-rail nanopower comparator output will alternate between VIN and GND depending on the

currents flowing into each of the two regulators. To design this control circuit, begin by looking at the case where

the two output currents are approximately equal and the comparator output is low. In this case, the output of the

TL1963A should be set the same as the fixed voltage regulator. The TL1963A-33 has a 3.3 V fixed output, so

this will be the set point for the adjustable regulator. Begin by selecting a R7 value less than 4.17 k

Ω. In this

example, 3.3 k

Ω will be used. R5 will need to have a high resistance to satisfy Equation 10, for this example 100

k

Ω was chosen. Then find the parallel resistance of R5 and R7 since they are both connected from the ADJ pin

to GND using Equation 6.

(6)

Once the R5 and R7 parallel resistance in calculated, the value for R6 can be found using Equation 7.

(7)

(8)

R6 = 5.45 k

Ω

(9)

In the case where the TL1963A-33 is sourcing more current than TL1963A, the comparator output will go high.

This will lower the voltage at the ADJ pin causing the TL1963A to try and raise the output voltage by sourcing

more current. The TL1963A-33 will then react by sourcing less current to try and keep the output from rising.

When the current through the TL1963A-33 becomes less than the TL1963A, the comparator output will return to

GND. In order for this to happen, Equation 10 must be satisfied:

(10)

(11)

0.19 V + 0.14 V < 1.21 V

(12)

0.33 V < 1.21 V

(13)

10.2.2.3 Application Curve

Figure 35. Parallel Regulators Sharing Load Current

20

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