LM6142 datasheet(11/15 Pages) NSC

11 / 15 page

LM6142/44 Application Ideas (Continued)

These features allow the LM6142 to drive capacitive loads

as large as 1000 pF at unity gain and not oscillate. The

scope photos (

Figure 3 and Figure 4) above show the

LM6142 driving a l000 pF load. In

Figure 3, the upper trace

is with no capacitive load and the lower trace is with a 1000

pF load. Here we are operating on ±12V supplies with a 20

Vp-p pulse. Excellent response is obtained with a C

f of l0 pF.

Figure 4, the supplies have been reduced to ±2.5V, the

pulse is 4 Vp-p and C

f is 39 pF. The best value for the com-

pensation capacitor is best established after the board layout

is finished because the value is dependent on board stray

capacity, the value of the feedback resistor, the closed loop

gain and, to some extent, the supply voltage.

Another effect that is common to all opamps is the phase

shift caused by the feedback resistor and the input capaci-

tance. This phase shift also reduces phase margin. This ef-

fect is taken care of at the same time as the effect of the ca-

pacitive load when the capacitor is placed across the

feedback resistor.

The circuit shown in

Figure 5 was used for these scope

photos.

Typical Applications

FISH FINDER/ DEPTH SOUNDER.

The LM6142/44 is an excellent choice for battery operated

fish finders. The low supply current, high gain-bandwidth and

full rail to rail output swing of the LM6142 provides an ideal

combination for use in this and similar applications.

DS012057-6

FIGURE 2.

DS012057-8

FIGURE 3.

DS012057-9

FIGURE 4.

DS012057-10

FIGURE 5.

LM6142 Scheda tecnica(PDF) 11 Page - National Semiconductor (TI)