RT9246APC datasheet(13/16 Pages) RICHTEK

13 / 16 page

RT9246A

DS9246A-04 March 2007

www.richtek.com

Referring to Figure 13, IX is expressed as:

where ILX_V is the valley of inductor current. To make sure

RT9246A could sense the valley current, right hand side

of Equation (1) should always be positive:

Since RCSN >> RCOMM in practical application, Equation (2)

could be simplified as:

For example, assuming the negative inductor valley current

−5A at no load, then for

OUT

LX_V

CSN

COMM

x R

I =

OUT

LX_V

CSN

COMM

x R

≥

OUT

LX_V

CSN

COMM

x R

≥

CSN

1.3V

-5A 1m

330

×Ω

≥

Figure13. Application circuit of GM

(2)

(1)

COMM

GMx

CSN

OUT

Figure 12

Load Line without dead zone at light loads

1.23

1.24

1.25

1.26

1.27

1.28

1.29

1.3

1.31

IOUT (A)

RCSN open

RCSN = 82k

w/o Dead Zone Compensation

w/i Dead Zone Compensation

RCOMM = 330

Ω, RADJ = 160Ω, VOUT = 1.300V

RCSN

≤ 85.8kΩ

Choose RCSN = 82k

Figure 12 shows that dead zone of load line at light load

is eliminated by applying this technique.

Error Amplifier Characteristic

For fast response of converter to meet stringent output

current transient response, RT9246A provides large slew

rate capability and high gain-bandwidth performance.

Figure 15. EA Falling Transient with 10pF Loading;

Slew Rate=8V/us

Figure 14. EA Rising Transient with 10pF Loading; Slew

Rate=8V/us

(2V/Div)

EA Falling Slew Rate

Time (250ns/Div)

VCOMP

VFB

500mV/Div)

(2V/Div)

EA Rising Slew Rate

Time (250ns/Div)

VCOMP

VFB

(500mV/Div)

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