ISL78310_15 Datasheet, PDF (11/14 Pages) Intersil Corporation – High Performance 1A LDO

ISL78310
I_OUT (1A/DIV)
I_OUT (1A/DIV)
V_OUT (1V/DIV)
TIME (1ms/DIV)
FIGURE 14. IN-RUSH CURRENT WITH NO C_SS, C_OUT = 1000µF,
IN-RUSH CURRENT = 1.8A
V_OUT (1V/DIV)
TIME (2ms/DIV)
FIGURE 15. IN-RUSH CURRENT WITH C_SS = 15nF, C_OUT = 1000µF,
IN-RUSH CURRENT = 0.5A
I_OUT (1A/DIV)
V_OUT (1V/DIV)
TIME (2ms/DIV)
FIGURE 16. IN-RUSH CURRENT WITH C_SS = 33nF, C_OUT = 1000µF, IN-RUSH CURRENT = 0.2A
Equation 3 can be used to calculate C_SS for a desired in-rush
current, where V_OUT is the output voltage, C_OUT is the total
capacitance on the output, and I_INRUSH is the desired in-rush
current.
C_SS = ^---^V----^O--_I--_I-^UN----^T-_R---^x-_U--^C--_S---^O-_H---^U-_x---^T-₀---_.x--₅-²--_V--^----^A-----^
(EQ. 3)
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 V_OUT.
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 V_IN. 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
1kR₁is then chosen according to Equation 5.
V_OUT
=
0.5 V




R^-R----12-
+
1

(EQ. 4)
R₁
=
R₂



-^V-₀---^O_.--₅--^U--_V--^T--
–
1_
(EQ. 5)
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FN7810.2
November 7, 2014