RT8296BHGSP Ver la hoja de datos (PDF) - Richtek Technology

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Fabricante

RT8296BHGSP

3A, 23V, 1.2MHz Synchronous Step-Down Converter

Richtek Technology 

RT8296B

To prevent enabling circuit when VIN is smaller than the VOUT target value, a resistive voltage divider can be placed

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

For example, if an 8V output voltage is regulated from a 12V input voltage, the resistor, REN2, can be selected to set

input lockout threshold larger than 8V.

VIN

12V

REN1

1C0INµF

2 VIN

BOOT 1

RT8296B

100k

SW 3

7 EN

CBOOT L

VOUT

8V

REN2

8 SS

CSS

4,

9 (Exposed Pad)

GND

FB 5

COMP 6

CC RC

R1

COUT

R2

CP

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

Hiccup Mode

For the RT8296BH, it provides Hiccup Mode Under Voltage

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

belowhalf of thefeedbackreferencevoltage,VFB, the UVP

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.

For the ripple current selection, the value of ∆IL = 0.24(IMAX)

will be a reasonable starting point. The largest 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 :

L

=





f

VOUT

× ∆IL(MAX)





×

1−

VOUT

VIN(MAX)





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,

VFB, the UVP will be triggered and the RT8296BL will shut

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 ∆IL increases with higher VIN

and decreases with higher inductance.

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

C ompo nen t

Supplier

Ser ies

D ime nsion s

(mm)

TDK

VLF10045 10 x 9.7 x 4.5

TDK

TAIYO

YUDEN

SLF12565

NR8040

12.5 x 12.5 x 6.5

8x8x4

∆IL

=





VOUT

f ×L





×

1−

VOUT

VIN





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.

CIN and COUT Selection

The input capacitance, CIN, is needed to filter the

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 :

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DS8296B-03 March 2011

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