RT4723P

Copyright © 2016 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation.

DS4723P-00

December

2016

www.richtek.com

11

Application Information

The RT4723P is a highly integrated Boost, LDO and

inverting charge pump to generate positive and

negative output voltages for AMLOED bias. It can

support input voltage range from 2.5V to 4.6V and the

voltage is generated from the LDO supplied from a

typical value of 4.6V. The Boost converter output also

drives an inverting charge pump controller to generate

value of

2.4V. The negative output voltage can be

programmed

through

the

dedicated

pin

which

implements single wire protocol and the available

voltage range is from

0.6V to 2.4V with 100mV per

step.

Input Capacitor Selection

Input ceramic capacitor with 4.7

F capacitance is

suggested for applications. For better voltage filtering,

select ceramic capacitors with low ESR, X5R and X7R

types are suitable because of their wider voltage and

temperature ranges.

Boost Inductor Selection

The inductance depends on the maximum input current.

As a general rule, the inductor ripple current range is

20% to 40% of the maximum input current. If 40% is

selected as an example, the inductor ripple current can

be calculated according to the following equations :

OUT

OUT(MAX)

IN(MAX)

IN

L

IN(MAX)

VI

I

=

V

I = 0.4 I









w

inductor ripple current. The input peak current can then

be obtained by adding the maximum input current with

half of the inductor ripple current as shown in the

following equation :

Note that the saturated current of the inductor must be

The

inductance

can

eventually

be

determined

according to the following equation :

  







2

2

IN

OUT

IN

OUT

OUT(MAX)

OSC

η

V

V

V

L

0.4

V

I

f















system performance, a shielded inductor is preferred to

avoid EMI problems.

Boost Output Capacitor Selection

The output ripple voltage is an important index for

estimating IC performance. This portion consists of two

parts. One is the product of ripple current with the ESR

of the output capacitor, while the other part is formed

by the charging and discharging process of the output

capacitor. As shown in Figure 1,

evaluated based on the ideal energy equalization.

According to the definition of Q, the

be calculated as the following equation :

OUT

OUT

OUT1

SOC

OUT

OUT1

SOC

OUT

1

Q = I

D

= C

V

f

ID

V

=

fC

 

 







cycle.

Finally, taking ESR into consideration, the overall

output ripple voltage can be determined by the

following equation :

OUT

OUT

ESR

OUT1

ESR

OSC

OUT

ID

V

= V

+ V

= V

+

fC













where

accordingly.