ISL78310 datasheet(11/14 Pages) RENESAS

11 / 14 page

ISL78310

FN7810 Rev 2.00

Page 11 of 14

November 7, 2014

Equation 3 can be used to calculate CSS for a desired in-rush

current, where VOUT is the output voltage, COUT is the total

capacitance on the output, and IINRUSH is the desired in-rush

current.

The scopes in Figures 14, 15 and 16 capture the response for the

soft-start function. The output voltage is set to 1.8V.

The external capacitor is always discharged to ground at the

beginning of start-up or enabling.

Power-Good Operation

The PGOOD is a logic output that indicates the status of VOUT.

The PGOOD flag is an open-drain NMOS that can sink 10mA

during a fault condition. The PGOOD pin requires an external

pull-up resistor, which is typically connected to the VOUT pin. The

PGOOD pin should not be pulled up to a voltage source greater

than VIN. The PGOOD goes low when the output voltage drops

below 84% of the nominal output voltage or if the part is

disabled. The PGOOD comparator functions during current limit

and thermal shutdown. For applications not using this feature,

connect this pin to ground.

Output Voltage Selection

An external resistor divider is used to scale the output voltage

relative to the internal reference voltage. This voltage is then fed

back to the error amplifier. The output voltage can be

programmed to any level between 0.8V and 5V. An external

resistor divider, R1 and R2, is used to set the output voltage as

shown in Equation 4. The recommended value for R2 is 500 to

R1is then chosen according to Equation 5.

FIGURE 14. IN-RUSH CURRENT WITH NO CSS, COUT = 1000µF,

IN-RUSH CURRENT = 1.8A

FIGURE 15. IN-RUSH CURRENT WITH CSS = 15nF, COUT = 1000µF,

IN-RUSH CURRENT = 0.5A

FIGURE 16. IN-RUSH CURRENT WITH CSS = 33nF, COUT = 1000µF, IN-RUSH CURRENT = 0.2A

VOUT (1V/DIV)

IOUT (1A/DIV)

TIME (1ms/DIV)

TIME (2ms/DIV)

IOUT (1A/DIV)

VOUT (1V/DIV)

TIME (2ms/DIV)

IOUT (1A/DIV)

VOUT (1V/DIV)

CSS

VOUTxCOUTx2A



IINRUSHx0.5V

---------------------------------------------------------

(EQ. 3)

VOUT

0.5V

------- 1









(EQ. 4)

VOUT

0.5V

---------------- 1

–







(EQ. 5)

ISL78310 Datasheet(PDF) 11 Page - Renesas Technology Corp

ISL78310 Datasheet(HTML) 11 Page - Renesas Technology Corp

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Datasheet Download

Link URL