ISL78310_15 Datasheet, PDF (10/14 Pages) Intersil Corporation – High Performance 1A LDO

ISL78310
TABLE 1.
V_OUT
(V)
R_TOP
R_BOTTOM
C_PB
(kΩ)
(Ω)
(pF)
C_OUT
(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.
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
overload condition is removed from V_OUT, then the output returns
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
(typically 1k to 10kwill be required for applications that use
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
SS pin to GND. An internal 2µA current source charges up this
C_SS and the feedback reference voltage is clamped to the
voltage across it. The start-up time of the regulator output
voltage for a given C_SS value can be calculated using Equation 2.
t_RAMP = -^C----^S----^S₂----_^x---⁰-_A---^.-⁵----^V---
(EQ. 2)
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,
external bulk capacitances on V_OUT where high levels of charging
current can be seen for a significant period of time. High in-rush
currents can cause V_IN to drop below minimum, which could
cause V_OUT to shutdown.
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FN7810.2
November 7, 2014