DESCRIPTION

The LT3045 is a high performance low dropout linear regulator featuring LTC’s ultralow noise and ultrahigh PSRR architecture for powering noise sensitive applications. Designed as a precision current reference followed by a high performance voltage buffer, the LT3045 can be easily paralleled to further reduce noise, increase output current and spread heat on the PCB.

The device supplies 500mA at a typical 260mV dropout voltage. Operating quiescent current is nominally 2.2mA and drops to <<1µA in shutdown. The LT3045’s wide output voltage range (0V to 15V) while maintaining unitygain operation provides virtually constant output noise, PSRR, bandwidth and load regulation, independent of the programmed output voltage. Additionally, the regulator features programmable current limit, fast start-up capability and programmable power good to indicate output voltage regulation.

The LT3045 is stable with a minimum 10µF ceramic output capacitor. Built-in protection includes reverse-battery protection, reverse-current protection, internal current limit with foldback and thermal limit with hysteresis. The LT3045 is available in thermally enhanced 12-Lead MSOP and 10-Lead 3mm × 3mm DFN packages.

 

CARACTÉRISTIQUES

Ultralow RMS Noise: 0.8µVRMS (10Hz to 100kHz)

Ultralow Spot Noise: 2nV/√Hz at 10kHz

Ultrahigh PSRR: 76dB at 1MHz

Output Current: 500mA

Wide Input Voltage Range: 1.8V to 20V

Single Capacitor Improves Noise and PSRR

100µA SET Pin Current: ±1% Initial Accuracy

Single Resistor Programs Output Voltage

High Bandwidth: 1MHz

Programmable Current Limit

Low Dropout Voltage: 260mV

Output Voltage Range: 0V to 15V

Programmable Power Good

Fast Start-Up Capability

Precision Enable/UVLO

Parallelable for Lower Noise and Higher Current

Internal Current Limit with Foldback

Minimum Output Capacitor: 10µF Ceramic

Reverse-Battery and Reverse-Current Protection

12-Lead MSOP and 10-Lead 3mm × 3mm DFN Packages

AEC-Q100 Qualified for Automotive Applications

 

CANDIDATURES

RF Power Supplies: PLLs, VCOs, Mixers, LNAs, PAs

Very Low Noise Instrumentation

High Speed/High Precision Data Converters

Medical Applications: Imaging, Diagnostics

Precision Power Supplies

Post-Regulator for Switching Supplies

 

 

INFORMATIONS SUR LES APPLICATIONS

The LT3045 is a high performance low dropout linear regulator featuring LTC’s ultralow noise (2nV/√Hz at 10kHz) and ultrahigh PSRR (76dB at 1MHz) architecture for powering noise sensitive applications. Designed as a precision current source followed by a high performance rail-to-rail voltage buffer, the LT3045 can be easily paralleled to further reduce noise, increase output current and spread heat on the PCB. The device additionally features programmable current limit, fast start-up capability and programmable power good.

The LT3045 is easy to use and incorporates all of the protection features expected in high performance regulators. Included are short-circuit protection, safe operating area protection, reverse battery protection, reverse current protection, and thermal shutdown with hysteresis.

 

Stability and Input Capacitance

The LT3045 is stable with a minimum 4.7µF IN pin capacitor. LTC recommends using low ESR ceramic capacitors. In cases where long wires connect the power supply to the LT3045’s input and ground terminals, the use of low value input capacitors combined with a large load current can result in instability. The resonant LC tank circuit formed by the wire inductance and the input capacitor is the cause and not because of LT3045’s instability. The self-inductance, or isolated inductance, of a wire is directly proportional to its length. The wire diameter, however, has less influence on its self-inductance. For example, the self-inductance of a 2-AWG isolated wire with a diameter of 0.26″ is about half the inductance of a 30-AWG wire with a diameter of 0.01″. One foot of 30-AWG wire has 465nH of self-inductance.

 

PSRR and Input Capacitance

For applications utilizing the LT3045 for post-regulating switching converters, placing a capacitor directly at the LT3045 input results in ac current (at the switching frequency) to flow near the LT3045. This relatively highfrequency switching current generates a magnetic field that couples to the LT3045 output, thereby degrading its effective PSRR. While highly dependent on the PCB, the switching pre-regulator, the input capacitance, amongst other factors, the PSRR degradation can be easily over 30dB at 1MHz. This degradation is present even if the LT3045 is de-soldered from the board, because it effectively degrades the PSRR of the PC board itself. While negligible for conventional low PSRR LDOs, LT3045’s ultrahigh PSRR requires careful attention to higher order parasitics in order to extract the full performance offered by the regulator