LM334MSLASHNOPB datasheet(5/25 Pages) TI1

5 / 25 page

LM134, LM234, LM334

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SNVS746C – MAY 2004 – REVISED MARCH 2005

Typical Performance Characteristics (continued)

Turn-On Voltage

Ratio of ISET to IBIAS

Figure 11.

Figure 12.

APPLICATION HINTS

The LM134 has been designed for ease of application, but a general discussion of design features is presented

here to familiarize the designer with device characteristics which may not be immediately obvious. These include

the effects of slewing, power dissipation, capacitance, noise, and contact resistance.

Calculating RSET

The total current through the LM134 (ISET) is the sum of the current going through the SET resistor (IR) and the

LM134's bias current (IBIAS), as shown in Figure 13.

Figure 13. Basic Current Source

A graph showing the ratio of these two currents is supplied under Ratio of ISET to IBIAS in Typical Performance

Characteristics. The current flowing through RSET is determined by VR, which is approximately 214μV/°K (64

mV/298°K

∼ 214μV/°K).

(1)

Since (for a given set current) IBIAS is simply a percentage of ISET, the equation can be rewritten

(2)

where n is the ratio of ISET to IBIAS as specified in Electrical Characteristics and shown in the graph. Since n is

typically 18 for 2

μA ≤ ISET ≤ 1mA, the equation can be further simplified to

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