NCV8870

www.onsemi.com

15

Table 3. OTA COMPENSATION TRANSFER FUNCTION AND COMPENSATION VALUES

10

desired_G

fc_gain_db

20

q

180°

p *

90°

p

180°

Select OTA Compensation Zero to Coincide

w

p1e

2

p

V

OUT

1

)

2

1

)

1

2

2

1

2

@

R

R

R

low

R

0

Low Frequency Zero (

1

2

R

R

1

*

1

* 4

R

R

2

C

1

High Frequency Zero (

1

2

R

R

1

)

1

* 4

R

R

2

C

1

Low Frequency Pole (

1

2

R

R

1

*

1

* 4

R

R

2

C

1

High Frequency Pole (

1

2

R

R

1

)

1

* 4

R

R

2

C

1

-G

0_OTA

1

) j

2

pf

w

z1e

1

) j

2

pf

w

p1e

1

) j

2

pf

w

z2e

1

) j

2

pf

w

p2e

The open-loop-response in closed-loop form to verify the

gain/phase margins may be obtained from the following

expression.

T(f)

+ G

Low Voltage Operation

If the input voltage drops below the UVLO or MOSFET

threshold voltage, another voltage may be used to power the

device. Simply connect the voltage you would like to boost

to the inductor and connect the stable voltage to the VIN pin

of the device. In boost configuration, the output of the

converter can be used to power the device. In some cases it

may be desirable to connect 2 sources to VIN pin, which can

be accomplished simply by connecting each of the sources

through a diode to the VIN pin.