ISL78310

FN7810 Rev 2.00

Page 10 of 14

November 7, 2014

Thermal Fault Protection

In the event the die temperature exceeds typically +160°C, then

the output of the LDO shuts down until the die temperature cools

down to typically +130°C. The level of power, combined with the

thermal resistance of the package (+48°C/W for DFN),

determines whether the junction temperature exceeds the

thermal shutdown temperature specified in the “Electrical

Specifications” on page 5 (see thermal packaging guidelines).

Current Limit Protection

The ISL78310 LDO incorporates protection against overcurrent

due to any short or overload condition applied to the output pin.

The current limit circuit performs as a constant current source

when the output current exceeds the current limit threshold

noted in the “Electrical Specifications” on page 5. If the short or

to normal voltage mode regulation. In the event of an overload

condition on the DFN package, the LDO will begin to cycle on and

off due to the die temperature exceeding thermal fault condition.

Functional Description

Enable Operation

The Enable turn-on threshold is typically 0.8V with a hysteresis of

80mV. The Enable pin does not have an internal pull-up or

pull-down resistor. As a result, this pin must not be left floating.

This pin must be tied to VIN if it is not used. A pull-up resistor

open collector or open drain outputs to control the Enable pin.

The Enable pin may be connected directly to VIN for applications

that are always on.

Soft-Start Operation

The soft-start circuit controls the rate at which the output voltage

rises up to regulation at power-up or LDO enable. This start-up

ramp time can be set by adding an external capacitor from the

voltage across it. The start-up time of the regulator output

The soft-start function also effectively limits the amount of

in-rush current to less than the programmed current limit during

start-up or an enable sequence, to avoid an overcurrent fault

condition. This can be an issue for applications that require large,

current can be seen for a significant period of time. High in-rush

TABLE 1.

(V)

(kΩ)

(Ω)

(pF)

(µF)

5.0

2.61

287

100

10

3.3

2.61

464

100

10

2.5

2.61

649

82

10

1.8

2.61

1.0k

82

10

1.5*

2.61

1.3k

68

10

1.5

2.61

1.3k

150

22

1.2*

2.61

1.87k

120

22

1.2*

2.61

1.87k

270

47

1.0

2.61

2.61k

220

47

0.8

2.61

4.32k

220

47

*Either option could be used, depending on cost/performance

requirements.

2

A

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

=

(EQ. 2)