RT6296F

Copyright © 2015 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS6296F-00

January

2015

www.richtek.com

9

Application Information

The RT6296F is a high voltage buck converter that can

support the input voltage range from 4.5V to 17V and

the input voltage range from 4.5V to 17V and the output

current can be up to 2A.

Output Voltage Selection

The resistive voltage divider allows the FB pin to sense

a fraction of the output voltage as shown in Figure 1.

RT6296F

GND

FB

R1

R2

R5

Figure 1. Output Voltage Setting

For adjustable voltage mode, the output voltage is set

by an external resistive voltage divider according to the

following equation :

OUT

FB

R1

V

V

1

R2









typ.). Table 2 lists the recommended resistors value for

common output voltages.

Table 2. Recommended Resistors Value

R1 (k

)

R2 (k

)

R5 (k

)

1.0

20.5

84.5

82

3.3

40.2

13

16

5.0

40.2

7.68

16

External Bootstrap Diode

Connect a 100nF low ESR ceramic capacitor between

the BOOT pin and SW pin. This capacitor provides the

gate driver voltage for the high side MOSFET. It is

recommended to add an external bootstrap diode

between an external 5V and BOOT pin, as shown as

Figure 2, for efficiency improvement when input voltage

is lower than 5.5V or duty ratio is higher than 65% .The

bootstrap diode can be a low cost one such as IN4148

or BAT54. The external 5V can be a 5V fixed input from

system or a 5V output (PVCC) of the RT6296F.

SW

BOOT

5V

RT6296F

100nF

Figure 2. External Bootstrap Diode

Inductor Selection

The inductor value and operating frequency determine

the ripple current according to a specific input and

output

higher VIN and decreases with higher inductance.

OUT

OUT

L

IN

VV

I1

f L

V





 

 







 

Having a lower ripple current reduces not only the ESR

losses in the output capacitors but also the output

voltage ripple. High frequency with small ripple current

can achieve highest efficiency operation. However, it

requires a large inductor to achieve this goal.

For the ripple current selection, the value of

ripple current occurs at the highest VIN. To guarantee

that the ripple current stays below the specified

maximum, the inductor value should be chosen

according to the following equation :

OUT

OUT

L(MAX)

IN(MAX)

VV

L1

f

I

V



 





 



 





 







 



The

inductor's

current

rating

(caused

a

40°C

temperature rising from 25°C ambient) should be

greater than the maximum load current and its

saturation current should be greater than the short

circuit peak current limit.

trapezoidal current at the source of the top MOSFET.

To prevent large ripple current, a low ESR input