Power Circuits for Instrumentation

The ADP5071 is a dual high performance dc-to-dc regulator that generates independently regulated positive and negative rails.

The input voltage range of 2.85 V to 15 V supports a wide variety of applications. The integrated main switch in both regulators enables generation of an adjustable positive output voltage up to +39 V and a negative output voltage down to −39 V below input voltage.

The ADP5071 operates at a pin selected 1.2 MHz/2.4 MHz switching frequency. The ADP5071 can synchronize with an external oscillator from 1.0 MHz to 2.6 MHz to ease noise filtering in sensitive applications. Both regulators implement programmable slew rate control circuitry for the MOSFET driver stage to reduce electromagnetic interference (EMI).

Flexible start-up sequencing is provided with the options of manual enable, simultaneous mode, positive supply first, and negative supply first.

The ADP5071 includes a fixed internal or resistor programmable soft start timer to prevent inrush current at power-up. During shutdown, both regulators completely disconnect the loads from the input supply to provide a true shutdown.

Other key safety features in the ADP5071 include overcurrent protection (OCP), overvoltage protection (OVP), thermal shutdown (TSD), and input undervoltage lockout (UVLO).

The ADP5071 is available in a 20-lead LFCSP or in a 20-lead TSSOP and is rated for a −40°C to +125°C junction temperature range.

Applications

• Bipolar amplifiers, ADCs, DACs, and multiplexers
• Charge-coupled device (CCD) bias supply
• Optical module supply
• RF power amplifier (PA) bias

The LT8609S is a compact, high efficiency, high speed synchronous monolithic step-down switching regulator that consumes only 1.7µA of non-switching quiescent current. The LT8609S can deliver 2A of continuous current with peak loads of 3A (<1sec) to support applications such as GSM transceivers which require high transient loads. Top and bottom power switches are included with all necessary circuitry to minimize the need for external components. Low ripple Burst Mode operation enables high efficiency down to very low output currents while keeping the output ripple below 10mV_P-P. A SYNC pin allows synchronization to an external clock, or spread spectrum modulation of switching frequencies for low EMI operation. Internal compensation with peak current mode topology allows the use of small inductors and results in fast transient response and good loop stability. The EN/UV pin has an accurate 1V threshold and can be used to program V_IN undervoltage lockout or to shut down the LT8609S reducing the input supply current to 1µA. A capacitor on the TR/SS pin programs the output voltage ramp rate during start-up while the PG flag signals when V_OUT is within ±8.5% of the programmed output voltage as well as fault conditions. The LT8609S is available in a small 16-lead 3mm × 3mm LQFN package.

Applications

• General Purpose Step Down
• Low EMI Step Down

The LT3045-1 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 LT3045-1 can be easily paralleled to further reduce noise, increase output current and spread heat on the PCB. In addition to the LT3045 feature set, the LT3045-1 incorporates a VIOC tracking function to control an upstream switching converter to maintain a constant voltage across the LT3045-1 and hence minimize power dissipation.

The device supplies 500mA at a typical 260mV dropout voltage. Operating quiescent current is nominally 2.3mA and drops to <<1μA in shutdown. The LT3045-1’s wide output voltage range (0V to 15V) while maintaining unity-gain 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 LT3045-1 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 LT3045-1 is available in thermally enhanced 12-Lead MSOP and 3mm × 3mm DFN packages.

Applications

• RF Power Supplies: PLLs, VCOs, Mixers, LNAs, PAs
• Very Low Noise Instrumentation
• High Speed/High Precision Data Converters
• Medical Applications: Imaging, Diagnostics
• Post-Regulator for Switching Supplies

The LT3094 is a high performance low dropout negative linear regulator featuring ADI’s ultralow noise and ultrahigh PSRR architecture for powering noise sensitive applications. The device can be easily paralleled to further reduce noise, increase output current and spread heat on a PCB.

The LT3094 supplies 500mA at a typical 235mV dropout voltage. Operating quiescent current is nominally 2.35mA and drops to 3µA in shutdown. The device’s wide output voltage range (0V to –19.5V) error amplifier operates in unity-gain and provides virtually constant output noise, PSRR, bandwidth, and load regulation independent of the programmed output voltage. Additional features are a bipolar enable pin, programmable current limit, fast startup capability and programmable power good to indicate output voltage regulation. The regulator incorporates a tracking function to control an upstream supply to maintain a constant voltage across the LT3094 to minimize power dissipation and optimize PSRR.

The LT3094 is stable with a minimum 10µF ceramic output capacitor. Built-in protection includes internal current limit with foldback and thermal limit with hysteresis. The LT3094 is available in thermally enhanced 12-Lead MSOP and 3mm × 3mm DFN Packages.

• RF and Precision Power Supplies
• Very Low Noise Instrumentation
• High Speed/High Precision Data Converters
• Medical Applications: Diagnostics and Imaging
• Post-Regulator for Switching Supplies

The LT3032 is a dual, low noise, positive and negative low dropout voltage linear regulator. Each regulator delivers up to 150mA with a typical 300mV dropout voltage. Each regulator’s quiescent current is low (30μA operating and <3μA in shutdown) and well-controlled in dropout, making it an excellent choice for battery-powered circuits.

Another key feature of the LT3032 is low output noise. Adding an external 10nF bypass capacitor to each regulator reduces output noise to 20μV_RMS/30μV_RMS over a 10Hz to 100kHz bandwidth. The LT3032 is stable with minimum output capacitors of 2.2μF. The regulators do not require the addition of ESR as is common with other regulators.

The regulators are offered as adjustable output devices with an output voltage down to the ±1.22V reference voltage or in fixed voltages of ±3.3V, ±5V, ±12V and ±15V. Internal protection circuitry includes reverse-output protection, current limiting and thermal limiting.

The LT3032 is available in a unique low profile 14-lead 4mm × 3mm × 0.75mm DFN package with exposed backside pads for each regulator, allowing optimum thermal performance.

Applications

• Battery-Powered Instruments
• Bipolar Power Supplies
• Low Noise Power Supplies

The LT3999 is a monolithic, high voltage, high frequency DC/DC transformer driver providing isolated power in a small solution footprint.

The LT3999 has two 1A current limited power switches that switch out of phase. The duty cycle is programmable to adjust the output voltage. The switching frequency is programmed up to 1MHz and can be synchronized to an external clock for more accurate placement of switcher harmonics. The input operating range is programmed with the precision undervoltage and overvoltage lockouts. The supply current is reduced to less than 1μA during shutdown. A user-defined RC time constant provides an adjustable soft-start capability by limiting the inrush current at start-up.

The LT3999 is available in a 10-lead MSOP and 3mm × 3mm DFN package with exposed pad.

Applications

• Low Noise Isolated Supplies
• Medical Instrument and Safety
• Distributed Power
• Multiple Output Supplies
• Positive-to-Negative Supplies
• Noise Immunity in Data Acquisition, RS232 and RS485

The ADuM6000 is an isolated DC/DC converter based on the Analog Devices, Inc., iCoupler^® technology. The DC/DC converter in this device provides regulated, isolated power in several combinations of input and output voltages as listed in Table 1 on the data sheet. The Analog Devices chip scale transformer iCoupler technology transfers isolated power in this DC/DC converter with up to 31% efficiency. The result is a small form factor, total isolation solution. Higher output power levels are obtained by using the ADuM6000 to augment the power output of the ADuM5401, ADuM5402, ADuM5403, ADuM5404, ADuM520x, and ADuM620x iCouplers with isoPower^®. isoPower^® uses high frequency switching elements to transfer power through its transformer. Special care must be taken during printed circuit board (PCB) layout to meet emissions standards. See the AN-0971 Application Note for board layout recommendations.

Applications

• USB peripheral power
• RS-232/RS-422/RS-485 transceiver power
• Industrial field bus power
• Power supply start-up bias
• Industrial PLCs

Modern microprocessors and microconverters are generally low power and operate on low supply voltages. Source and sink current for 2.5 V CMOS logic outputs ranges from μA to mA . Driving an H-bridge switching 12 V with a 4 A peak current requires the use of carefully selected interface and level translation components, especially if low jitter is needed.

The ADG787 is a low voltage CMOS device that contains two independently selectable single-pole double-throw (SPDT) switches. With a 5 V dc power supply, a voltage as low as 2 V is a valid high input logic voltage. Therefore, the ADG787 provides appropriate level translation from the 2.5 V controlling signal to the 5 V logic level needed to drive the ADuM7234 half-bridge driver.

The ADuM7234 is an isolated, half-bridge gate driver that employs Analog Devices’ iCoupler^® technology to provide independent and isolated high-side and low-side outputs making it possible to use N-channel MOSFETs exclusively in the H-bridge. There are several benefits in using N-channel MOSFETs: N-channel MOSFETs typically have one third of the on resistance of P-channel MOSFETs and higher maximum current; they switch faster, thereby reducing power dissipation; and the rise time and fall time is symmetrical.

The 4 A peak drive current of the ADuM7234 ensures that the power MOSFETs can switch on and off very fast, thereby minimizing the power dissipation in the H-bridge stage. The maximum drive current of the H-bridge in this circuit can be up to 85 A, which is limited by the maximum allowable MOSFET current.

The ADuC7061 is a low power, ARM7 based precision analog microcontroller with integrated pulse width modulated (PWM) controllers that have outputs that can be configured to drive an H-bridge after suitable level translation and conditioning.

Figure 1. H-Bridge Using ADuM7234 Isolated Half-bridge Driver (Simplified Schematic: All Connections and Decoupling Not Shown)

The system functional diagram in Figure 1 is a precision analog front end for measurement of current down to the femtoampere range. This industry-leading solution is ideal for chemical analyzers and laboratory grade instrument where an ultrahigh sensitivity analog front end is required for signal conditioning current output sensors such as photodiodes, photomultiplier tubes, and Faraday cups. Applications that can use this solution include mass spectrometry, chromatography, and coulometry.

The EVAL-CN0407-SDPZ provides a reference design for real-world application by partitioning the system into a low-leakage mezzanine board and a data acquisition board. The input signal conditioning is implemented with the ADA4530-1 on the mezzanine board. The ADA4530-1 is an electrometer-grade amplifier with ultralow input bias current of 20 fA maximum at 85°C. A guard buffer is integrated on the chip to isolate the input pins from leakage to the printed circuit board (PCB). The default amplifier configuration is in the transimpedance mode with a 10 GΩ glass resistor and a metal shield that prevents leakage current from entering any of the high impedance paths on the board. In addition, the mezzanine board includes unpopulated resistor and capacitor pads to allow prototyping with surfacemount feedback resistors as well as other input configurations.

The data acquisition board uses an AD7172-2 24-bit Σ-Δ analog-to-digital-converter (ADC) and is powered from a single 9 V dc supply. The on-board supply generates all necessary voltages required to power both boards. The board connects to a PC via the SDP-S board (EVAL-SDP-CS1Z) and uses digital isolation to prevent noise from the USB bus or ground loops from degrading low current measurements.