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.

 

FEATURES

-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

 

APPLICATIONS

-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

 

APPLICATIONS INFORMATION

The LT3045 is a high performance low dropout linear regulator featuring LTC’s ultralow noise 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.

 

Output Voltage

The LT3045 incorporates a precision 100µA current source flowing out of the SET pin, which also ties to the error amplifier’s inverting input. This reference voltage is simply the product of the SET pin current and the SET pin resistor. The error amplifier’s unity-gain configuration produces a low impedance version of this voltage on its noninverting input, i.e. the OUTS pin, which is externally tied to the OUT pin.
The benefit of using a current reference compared with a voltage reference as used in conventional regulators is that the regulator always operates in unity gain configuration, independent of the programmed output voltage. This allows the LT3045 to have loop gain, frequency response and bandwidth independent of the output voltage. As a result, noise, PSRR and transient performance do not change with output voltage. Moreover, since none of the error amp gain is needed to amplify the SET pin voltage to a higher output voltage, output load regulation is more tightly specified in the hundreds of microvolts range and not as a fixed percentage of the output voltage. The LT3045 requires an output capacitor for stability. Given its high bandwidth, LTC recommends low ESR and ESL ceramic capacitors. A minimum 10µF output capacitance with an ESR below 20mΩ and an ESL below 2nH is required for stability.