RT8296B

10

DS8296B-03

March 2011

www.richtek.com

between the input voltage and ground and connected to the EN pin to adjust IC lockout threshold, as shown in Figure 4.

input lockout threshold larger than 8V.

VIN

EN

GND

BOOT

FB

SW

7

5

2

3

1

L

R1

R2

RT8296B

SS

8

COMP

6

4,

9 (Exposed Pad)

100k

8V

10

µF

12V

Figure 4. The Resistors can be Selected to Set IC Lockout Threshold

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.

OUT

OUT

L(MAX)

IN(MAX)

VV

L =1

f

IV



 

×−



 

×∆



 

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. Please

see Table 2 for the inductor selection reference.

Table 2. Suggested Inductors for Typical

Application Circuit

Component

Supplier

Series

Dimensions

(mm)

TDK

VLF10045

10 x 9.7 x 4.5

TDK

SLF12565

12.5 x 12.5 x 6.5

TAIYO

YUDEN

NR8040

8 x 8 x 4

trapezoidal current at the source of the high side MOSFET.

To prevent large ripple current, a low ESR input capacitor

sized for the maximum RMS current should be used. The

RMS current is given by :

Hiccup Mode

For the RT8296BH, it provides Hiccup Mode Under Voltage

Protection (UVP) is provided. When the FB voltage drops

function will be triggered and the RT8296BH will shut down

for a period of time and then recover automatically. The

Hiccup Mode UVP can reduce input current in short-circuit

conditions.

Latch-Off Mode

For the RT8296BL, it provides Latch-Off Mode Under

Voltage Protection (UVP) is provided. When the FB

voltage drops below half of the feedback reference voltage,

down in Latch-Off Mode. In shutdown condition, the

RT8296BL can be reset via the EN pin or power input VIN.

Inductor Selection

The inductor value and operating frequency determine the

ripple current according to a specific input and output

voltage. The ripple current

and decreases with higher inductance.

OUT

OUT

L

IN

VV

I =1

f LV



 

∆

×−



 

×



 

For the ripple current selection, the value of

will be a reasonable starting point. The largest ripple

ripple current stays below the specified maximum, the

inductor value should be chosen according to the following

equation :