ISL78310 datasheet(9/14 Pages) RENESAS

9 / 14 page

ISL78310

FN7810 Rev 2.00

Page 9 of 14

November 7, 2014

Applications Information

Input Voltage Requirements

The ISL78310 is capable of delivering output voltages from 0.8V

to 5.0V. Due to the nature of an LDO, VIN must be some margin

higher than the output voltage plus dropout at the maximum

rated current of the application if active filtering (PSRR) is

expected from VIN to VOUT. The generous dropout specification of

this family of LDOs allows applications to design for a level of

efficiency that can accommodate profiles smaller than the

TO220/263.

External Capacitor Requirements

GENERAL GUIDELINE

External capacitors are required for proper operation. Careful

attention must be paid to layout guidelines and selection of

capacitor type and value to ensure optimal performance.

OUTPUT CAPACITOR

The ISL78310 applies state of the art internal compensation to

keep the selection of the output capacitor simple for the

customer. Stable operation over full temperation, VIN range, VOUT

range and load extremes are guaranteed for all capacitor types

and values assuming a minimum of 10µF X5R/X7R is used for

local bypass on VOUT. This output capacitor must be connected to

the VOUT and GND pins of the LDO with PCB traces no longer than

0.5cm. Additional capacitors of any value in ceramic, POSCAP,

alum/tantalum electrolytic types may be placed in parallel to

improve PSRR at higher frequencies and/or load transient AC

output voltage tolerances.

INPUT CAPACITOR

For proper operation, a minimum capacitance of 10µF X5R/X7R

is required at the input. This ceramic input capacitor must be

connected to VIN and GND pins of the LDO with PCB traces no

longer than 0.5cm.

Phase Boost Capacitor (CPB)

A small phase boost capacitor, CPB, can be placed across the top

resistor in the feedback resistor divider network (Figure 13) in

order to place a zero at:

This zero increases the crossover frequency of the LDO and

provides additional phase resulting in faster load transient

response.

It is also important to note that the LDO stability and load transient

are affected by the type of output capacitor used. For optimal

result, empirical tuning of CPB is suggested for each specific

application. It is recommended to not use CPB when high ESR

capacitors such as aluminum electrolytic or tantalum are used.

Table 1 shows the recommended CPB, RTOP, RBOTTOM and CPB

values for different output voltage rails.

FIGURE 12. SPECTRAL NOISE DENSITY vs FREQUENCY

Typical Operating Performance Unless otherwise noted: V

IN = 2.2V, VOUT = 1.8V, CIN = COUT = 10µF, TJ = +25°C,

IL = 0A. (Continued)

0.001

0.01

0.1

100

10k

100k

10M

FREQUENCY (Hz)

ILOAD = 1A

(EQ. 1)

12 pi RTOP CPB







ISL78310

CIN

RTOP

RBOTTOM

CPB

VIN

VOUT

COUT

ADJ

FIGURE 13.

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