Datenblatt-Suchmaschine für elektronische Bauteile |
|
TP3-470 Datenblatt(PDF) 6 Page - Linear Technology |
|
TP3-470 Datenblatt(HTML) 6 Page - Linear Technology |
6 / 12 page 6 LTC1504A APPLICATIONS INFORMATION 3 Ω, depending on supply voltage. This high power pulse train is filtered by the external inductor and capacitor, providing a steady DC value at the output node. This node returns to FB or SENSE, closing the loop. The LTC1504A includes a second feedback loop that controls operation in current limit. The ILIM amplifier monitors the voltage at the SW pin while Q1 is on. It compares this voltage to the voltage at the IMAX pin. As the peak current through Q1 rises, the voltage drop across it due to its RON increases proportionally. When SW drops below IMAX, indicating the current through Q1 has in- creased beyond the desired value, ILIM starts pulling a controlled amount of current out of SS, the external soft start pin. As SS falls, it pulls COMP down with it, limiting the duty cycle and reducing the output voltage to control the current. The speed at which the current limit circuit reacts is set by the value of the external soft start capacitor. EXTERNAL COMPONENT SELECTION External components required by the LTC1504A fall into three categories: input bypass, output filtering and com- pensation. Additional components to set up soft start and current limit are usually included as well. A minimum LTC1504A circuit can be constructed with as few as four external components; a circuit that utilizes all of the LTC1504A’s functionality usually includes eight or nine external components, with two additional feedback resis- tors required for adjustable parts. See the Typical Applica- tions section for examples of external component hookup. Input Bypass The input bypass capacitor is critical to proper LTC1504A operation. The LTC1504A includes a precision reference and a pair of high power switches feeding from the same VCC pin. If VCC does not have adequate bypassing, the switch pulses introduce enough ripple at VCC to corrupt the reference voltage and the LTC1504A will not regulate accurately. Symptoms of inadequate bypassing include poor load regulation and/or erratic waveforms at the SW pin. If an oscilloscope won’t trigger cleanly when looking at the SW pin, the LTC1504A doesn’t have adequate input bypass. output bypass capacitors and a compensation network complete the control loop. The LTC1504A adjustable output parts require an additional pair of resistors to set the output voltage. The LTC1504A-3.3 parts include an onboard resistor divider preset to a 3.3V output voltage. A functional 3.3V output regulator can be constructed with an LTC1504A-3.3 and as few as four external components. The LTC1504A feedback loop includes a precision refer- ence trimmed to 1% (VREF), a wide bandwidth transconductance feedback amplifier (FB) and an onboard PWM generator (SAW and PWM). The PWM generator is capable of generating pulse widths from 0% to 100%, minimizing dropout and maximizing transient response. The internal sawtooth oscillator typically runs at 200kHz. Q1 and Q2 are capable of carrying peak currents in excess of 500mA, with the continuous output power level limited primarily by the thermal dissipation of the SO-8 package. With a 5V input and a 3.3V output, the LTC1504A can supply 500mA of continuous output current with an appropriate layout. An on-chip current limit circuit, set with a single external resistor, can be used to help limit power dissipation. See the Thermal Considerations sec- tion for more information. Theory of Operation The LTC1504A primary feedback loop consists of the main error amplifier FB, the PWM generator, the output drive logic and the power switches. The loop is closed with the external inductor and the output bypass capacitor. The feedback amplifier senses the output voltage directly at the SENSE pin for fixed output versions or through an external resistor divider in the adjustable output version. This feedback voltage is compared to the 1.265V internal reference voltage by FB and an error signal is generated at the COMP pin. COMP is a high impedance node that is brought out to an external pin for optimizing the loop compensation. COMP is compared to a 200kHz sawtooth wave by com- parator PWM. The output stage takes the PWM signal and generates nonoverlapping drive for the onboard P- and N- channel power MOSFETs, which drive the SW pin with a low impedance image of the PWM waveform. Typical open-loop output impedance at SW is between 1 Ω and |
Ähnliche Teilenummer - TP3-470 |
|
Ähnliche Beschreibung - TP3-470 |
|
|
Link URL |
Privatsphäre und Datenschutz |
ALLDATASHEETDE.COM |
War ALLDATASHEET hilfreich? [ DONATE ] |
Über Alldatasheet | Werbung | Kontakt | Privatsphäre und Datenschutz | Linktausch | Hersteller All Rights Reserved©Alldatasheet.com |
Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
Family Site : ic2ic.com |
icmetro.com |