LM321

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SNOS935C – FEBRUARY 2001 – REVISED DECEMBER 2014

Typical Applications (continued)

8.2.7 Lamp Driver

Similar to the LED driver, LM321 can be used as a lamp driver. The output of the amplifier is to be connected to

the base of a bipolar transistor which will drive

β*output current of the amplifier through the lamp.

Figure 14. Lamp Driver Schematic

9 Power Supply Recommendations

The LM321 is specified for operation up to 32 V; many specifications apply from –40°C to 85°C. Parameters that

can exhibit significant variance with regard to operating voltage or temperature are presented in Typical

Characteristics. Place 0.1-

μF bypass capacitors close to the power-supply terminals to reduce errors coupling in

from noisy or high-impedance power supplies. For more detailed information on bypass capacitor placement, see

Layout.

10 Layout

10.1 Layout Guidelines

For best operational performance of the device, use good printed circuit board (PCB) layout practices, including:

•

Noise can propagate into analog circuitry through the power pins of the circuit as a whole and operational

amplifer itself. Bypass capacitors are used to reduce the coupled noise by providing low-impedance power

sources local to the analog circuitry.

–

Connect low-ESR, 0.1-

μF ceramic bypass capacitors between each supply pin and ground, placed as

close to the device as possible. A single bypass capacitor from V+ to ground is applicable for single

supply applications.

•

Separate grounding for analog and digital portions of circuitry is one of the simplest and most-effective

methods of noise suppression. One or more layers on multilayer PCBs are usually devoted to ground planes.

A ground plane helps distribute heat and reduces EMI noise pickup. Make sure to physically separate digital

and analog grounds paying attention to the flow of the ground current. For more detailed information refer to

Circuit Board Layout Techniques, SLOA089.

•

In order to reduce parasitic coupling, run the input traces as far away from the supply or output traces as

possible. If it is not possible to keep them separate, it is much better to cross the sensitive trace perpendicular

as opposed to in parallel with the noisy trace.

•

Place the external components as close to the device as possible. As shown in Figure 15, keeping RF and

RG close to the inverting input minimizes parasitic capacitance.

•

Keep the length of input traces as short as possible. Always remember that the input traces are the most

sensitive part of the circuit.

•

Consider a driven, low-impedance guard ring around the critical traces. A guard ring can significantly reduce

leakage currents from nearby traces that are at different potentials.

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