ОСОБЕННОСТИ

Programmable 2-Terminal Current Source

Maximum Output Current: 200mA

Wide Input Voltage Range: 1.2V to 40V

Input/Output Capacitors Not Required

Resistor Ratio Sets Output Current

Initial Set Pin Current Accuracy: 1%

Reverse-Voltage Protection

Reverse-Current Protection

<0.001%/V Line Regulation Typical

Current Limit and Thermal Shutdown Protection

Available in 8-Lead SOT-23, 3-Lead SOT-223 and 8-Lead 3mm × 3mm DFN Packages

AEC-Q100 Qualified for Automotive Applications

 

ПРИЛОЖЕНИЯ

2-Terminal Floating Current Source

GND Referred Current Source

Variable Current Source

In-Line Limiter

Intrinsic Safety Circuits&nbsp

 

ОПИСАНИЕ

The LT®3092 is a programmable 2-terminal current source. It requires only two resistors to set an output current between 0.5mA and 200mA. A multitude of analog techniques lend themselves to actively programming the output current. The LT3092 is stable without input and output capacitors, offering high DC and AC impedance. This feature allows operation in intrinsically safe applications.

The SET pin features 1% initial accuracy and low temperature coefficient. Current regulation is better than 10ppm/V from 1.5V to 40V.

The LT3092 can operate in a 2-terminal current source configuration in series with signal lines. It is ideal for driving sensors, remote supplies, and as a precision current limiter for local supplies.

Internal protection circuitry includes reverse-battery and reverse-current protection, current limiting and thermal limiting. The LT3092 is offered in the 8-lead TSOT-23, 3-lead SOT-223 and 8-lead 3mm × 3mm DFN packages.

 

ИНФОРМАЦИЯ О ПРИЛОЖЕНИЯХ

Introduction

The LT3092 is a versatile IC that operates as a 2-terminal programmable current source with the addition of only two external resistors; no external bypass capacitors are needed for stability.

The LT3092 is easy to use and has all the protection fea tures expected in high performance products. Included are reverse-voltage protection, reverse-current protection, short-circuit protection and thermal shutdown with hysteresis.

The LT3092 operates with or without input and output capacitors. The simplest current source application requires only two discrete resistors to set a constant output current up to 200mA. A variety of analog techniques lend themselves to regulating and varying the current source value.

The device utilizes a precision “0” TC 10μA reference cur rent source to program output current. This 10µA cur rent source connects to the noninverting input of a power operational amplifier. The power operational amplifier provides a low impedance buffered output of the voltage on the noninverting input.

Many application areas exist in which operation without input and output capacitors is advantageous. A few of these applications include sensitive circuits that cannot endure surge currents under fault or overload conditions and intrinsic safety applications in which safety regulations limit energy storage devices that may spark or arc.

Programming Output Current in 2-Terminal Current Source Mode

Setting the LT3092 to operate as a 2-terminal current source is a simple matter. The 10µA reference current from the SET pin is used with one resistor to generate a small voltage, usually in the range of 100mV to 1V (200mV is a level that will help reject offset voltage, line regulation, and other errors without being excessively large). This voltage is then applied across a second resistor that connects from OUT to the first resistor. Figure 1 shows connections and formulas to calculate a basic current source configuration.

With a 10μA current source generating the reference that gains up to set output current, leakage paths to or from the SET pin can create errors in the reference and output currents. High quality insulation should be used (e.g., Teflon, Kel-F). The cleaning of all insulating surfaces to remove fluxes and other residues may be required. Surface coating may be necessary to provide a moisture barrier in high humidity environments.

Minimize board leakage by encircling the SET pin and circuitry with a guard ring operated at a potential close to itself; tie the guard ring to the OUT pin. Guarding both sides of the circuit board is required. Bulk leakage reduction depends on the guard ring width. Ten nanoamperes of leakage into or out of the SET pin and its associated circuitry creates a 0.1% reference current error. Leakages of this magnitude, coupled with other sources of leakage, can cause significant offset voltage and reference current drift, especially over the possible operating temperature range.