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LTC1514-3.3 Fiches technique(PDF) 5 Page - Linear Technology |
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LTC1514-3.3 Fiches technique(HTML) 5 Page - Linear Technology |
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5 / 8 page  5 LTC1514-3.3/LTC1514-5 PIN FUNCTIONS battery comparator and 1.145V reference are kept alive in shutdown. GND (Pin 4): Ground. Should be tied to a ground plane for best performance. C1– (Pin 5): Charge Pump Flying Capacitor, Negative Terminal. C1+ (Pin 6): Charge Pump Flying Capacitor, Positive Terminal. VIN (Pin 7): Charge Pump Input Voltage. May be between 2V and 8V (LTC1514-3.3) or between 2.7V and 10V (LTC1514-5). VIN should be bypassed with a ≥10µF low ESR capacitor as close as possible to the pin for best performance. VOUT (Pin 8): Regulated Output Voltage. The output volt- age is internally set to either 3.3V (LTC1514-3.3) or to 5V (LTC1514-5) using an internal resistor divider. VOUT should be bypassed with a ≥10µF low ESR capacitor as close as possible to the pin for best performance. APPLICATIONS INFORMATION Regulator Operation The regulator section of the LTC1514-3.3/LTC1514-5 consists of a charge pump, reference, comparator and some logic. The divided down output voltage is com- pared to the internal reference voltage. When the divided output drops below the reference voltage, the charge pump is enabled, which boosts the output back into regulation. Hysteresis in the comparator forces the regu- lator to burst on and off and causes approximately 100mV of peak-to-peak ripple to appear at the output. By enabling the charge pump only when needed, the LTC1514-3.3 and LTC1514-5 are able to achieve high efficiencies with low output load currents. Each part’s charge pump has a unique architecture that allows the input voltage to be either stepped up or stepped down to produce a regulated output. Internal circuitry senses the VIN to VOUT differential voltage and controls the charge pump operating mode. In addition, the effective output impedance of the charge pump is internally adjusted to prevent large inrush currents and allow for a wide input voltage range. When the input voltage is lower than the output voltage, the charge pump operates as a step-up voltage doubler. When the input voltage is greater than the output, the charge pump operates as a step-down gated switch. Capacitor Selection For best performance, low ESR capacitors are recom- mended for both CIN and COUT to reduce noise and ripple. The CIN and COUT capacitors should be either ceramic or tantalum and should be 10 µF or greater. If the input source impedance is very low (< 0.5 Ω), CIN may not be needed. Increasing the size of COUT to 22µF or greater will reduce output voltage ripple—particularly with high VIN voltages (8V or greater). A ceramic capacitor is recom- mended for the flying capacitor C1 with a value of 0.1 µF or 0.22 µF. Smaller value flying capacitors may be used in low output current applications. Output Ripple Normal LTC1514-3.3/LTC1514-5 operation produces voltage ripple on the VOUT pin. Output voltage ripple is required for the parts to regulate. 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 resistance) in the output capacitor. Typical output ripple (VIN < 8V) under maxi- mum load is 100mV peak-to-peak with a low ESR (< 0.5 Ω) 10 µF output capacitor. For applications requiring VIN to exceed 8V, a 22 µF or larger COUT capacitor is recom- mended to maintain max ripple in the 100mV range. The magnitude of the ripple voltage depends on several factors. High input voltages increase the output ripple since more charge is delivered to COUT per charging cycle. A large C1 flying capacitor (> 0.22 µF) also increases ripple in step-up mode for the same reason. Large output current load and/or a small output capacitor (< 10 µF) results in higher ripple due to higher output voltage dV/dt. High ESR capacitors (ESR > 0.5 Ω) on the |
Numéro de pièce similaire - LTC1514-3.3 |
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Description similaire - LTC1514-3.3 |
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