LTC1986 datasheet(6/8 Pages) LINER

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LTC1986

1986fa

Output Ripple

Normal 5V mode operation produces voltage ripple on the

VOUT pin. Output voltage ripple is required for regulation.

Low frequency ripple exists due to the hysteresis in the

sense comparator and propagation delays in the charge

pump enable/disable circuits. High frequency ripple is

also present mainly from the ESR (equivalent series resis-

tance) in the output capacitor. Typical output ripple with

VIN = 3V under maximum load is 75mVP-P with a low ESR

2.2

µF output capacitor and a 0.047µF C1 capacitor. For

applications requiring VIN to exceed 3.3V or for applica-

tions requiring < 75mV of peak-to-peak ripple, a 3.3

µF to

µF COUT capacitor is recommended. Slight further de-

creases in output ripple can be achieved by using COUT

capacitors larger than 10

µF.

APPLICATIONS INFORMATION

Protection Features

The LTC1986 provides several protection features.

Undervoltage lockout prevents any current from flowing

between VIN and VOUT until the VIN voltage

exceeds 1.4V (typ). This prevents undesirable glitches

during power-up. The parts also limit inrush current

during power-up to under 200mA regardless of VIN volt-

age, operating mode and output load by disabling the main

direct connect switch (3V mode) or the charge pump

(5V mode) and enabling a 50

Ω series switch between VIN

and VOUT until VOUT reaches VIN/2. The parts are also

short-circuit protected and can survive an indefinite short

from VOUT to GND regardless of operating mode or input

voltage. In the event of thermal overload, the parts will

enter thermal shutdown if the junction temperature

exceeds 165

°C and return to normal operation once the

junction temperature drops to 150

°C.

LTC1986 Datasheet(PDF) 6 Page - Linear Technology