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LTC1514CS8-3.3 Datasheet(PDF) 6 Page - Linear Technology |
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LTC1514CS8-3.3 Datasheet(HTML) 6 Page - Linear Technology |
6 / 8 page 6 LTC1514-3.3/LTC1514-5 APPLICATIONS INFORMATION output pin cause high frequency voltage spikes on VOUT with every clock cycle. There are several ways to reduce the output voltage ripple. A larger COUT capacitor (22µF or greater) will reduce both the low and high frequency ripple due to the lower COUT charging and discharging dV/dt and the lower ESR typically found with higher value (larger case size) capacitors. A low ESR ceramic output capacitor will minimize the high frequency ripple, but will not reduce the low frequency ripple unless a high capacitance value is chosen. A reasonable compromise is to use a 10 µF to 22 µF tantalum capacitor in parallel with a 1µF to 3.3µF ceramic capacitor on VOUT to reduce both the low and high frequency ripple. An RC or LC filter may also be used to reduce high frequency voltage spikes (see Figure 1). Internal soft start circuitry controls the rate at which VOUT may be charged from 0V to its final regulated value. The typical start-up time from VOUT = 0V to 5V is 4ms. This corresponds to an effective VOUT charging current of only 12.5mA for a 10 µF output capacitor (27.5mA for 22µF, etc). Note that any output current load present during start-up will add directly to the charging currents men- tioned above. The soft start circuitry limits start-up current both at initial power-up and when coming out of shutdown. As the VIN (or boosted VIN) to VOUT voltage differential grows, the effective output impedance of the charge pump is automatically increased by internal voltage sensing circuitry. This feature minimizes the current spikes pulled from VIN whenever the charge pump is enabled and helps to reduce both input and output ripple. Protection Features The LTC1514-X contain thermal shutdown and short- circuit protection features. The parts will shut down when the junction temperature reaches approximately 150 °C and will resume operation once the junction temperature has dropped back to approximately 140 °C. The parts will limit output current to 12mA (typ) when a short-circuit condition (VOUT < 100mV) exists. The parts can survive an indefinite short to GND. The LTC1514-X devices use a low thermal resistance SO-8 package (110 °C/W vs 150 °C/W for standard SO-8). This permits full output current, even at high input supply voltages. Low-Battery Comparator The internal low-battery comparator trips at 1.145 ±3% (LBI ramping negative). Programming the comparator to trip at a higher voltage can easily be done with an external LTC1514-X VOUT VOUT 8 15 µF TANTALUM 2 Ω 1 µF CERAMIC LTC1514-X VOUT 1514 F01 VOUT 8 10 µF TANTALUM + + 10 µF TANTALUM + Figure 1. Output Ripple Reduction Techniques Inrush Currents A common problem with switched capacitor regulators is inrush current — particularly during power-up and coming out of shutdown mode. Whenever large VIN (or boosted VIN) to VOUT voltage differentials are present, most charge pumps will pull large current spikes from the input supply. Only the effective charge pump output impedance limits the current while the charge pump is enabled. This may disrupt input supply regulation, espe- cially if the input supply is a low power DC/DC converter or linear regulator. The LTC1514-3.3/LTC1514-5 mini- mize inrush currents both at start-up and under normal high VIN to VOUT operation. Figure 2. Programming the Low-Battery Comparator Trip Voltage 1 2 3 4 8 7 6 5 SHDN LBO LBI GND VOUT VIN C1+ C1– LTC1514-X R2 R1 VTRIP = 1.145V(1 + R1/R2) (LBI RAMPING NEGATIVE) 1514 F02 VBAT |
Similar Part No. - LTC1514CS8-3.3 |
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Similar Description - LTC1514CS8-3.3 |
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