BUF04

REV. 0

–10–

A two-terminal equivalent circuit of the BUF04 is shown in

Figure 30 where the transistor-level equivalent circuit is reduced

to its essential elements. The input stage develops a signal

30

Ω, the voltage gain of the BUF04, given by the ratio R

approximately 13,000—accurate to approximately 13.5 bits.

The BUF04’s open-loop ac transimpedance response is

50 kHz.

X1

XI

RFB = 100

Ω

Ω

Ω

Figure 30. Current-Feedback Functional Equivalent

Circuit of the BUF04

Grounding and Bypassing Considerations

To take full advantage of the BUF04’s very wide bandwidth,

high slew rates, and dynamic range capabilities requires due

diligence with regard to supply bypassing. In high speed circuits,

the supply bypassing network must provide a very low impedance

return path for currents flowing to and from the load network.

As with any high speed application, multiple bypassing is always

recommended. A 10

µF tantalum electrolytic in parallel with a

0.1

µF ceramic capacitor is sufficient for most applications. For

those high speed applications where output load currents

approach 50 mA, small valued resistors (1.1

Ω to 4.7 Ω) in

series with the tantalum capacitors may improve circuit

transient response by damping out the capacitor’s self-

inductance. Figure 31 illustrates bypassing recommendations.

BUF04

7

6

10µF R1

0.1µF

V+

0.1µF

V–

10µF

R2

4

3

KELVIN RETURN

FOR LOAD CURRENT

KELVIN RETURN

FOR LOAD CURRENT

NOTE

USE SHORT LEAD LENGTHS (<5mm)

Figure 31. Recommended Power-Supply Bypassing

To minimize the effects of high-frequency coupling, circuits

must be built with short interconnect leads, and large ground

planes should he used whenever possible to provide a low

resistance, low-inductance circuit path. Sockets should be

avoided because the increased interlead capacitance can degrade

bandwidth and stability. If sockets are necessary, individual pin

sockets (oftentimes called “cage jacks,” AMP Part No.

5-330808-3 or 5-330808-6) should be used. They contribute far

less stray reactance than molded socket assemblies.

Offset Voltage Nulling

Although the offset voltage of the BUF04 is very low (1 mV,

maximum) for such a high speed buffer, the circuit shown in

Figure 32 can be used if additional offset voltage nulling is

required. A potentiometer ranging from 1 k to 10 k can be used

Ω potentiometer, the trim range is

±30 mV.

V+

BUF04

7

6

10µF

0.1µF

0.1µF

V–

10µF

4

3

10k

1

TRIM RANGE

±30mV

8

Figure 32. Optional Offset Voltage Nulling Scheme

APPLICATIONS

Output Short-Circuit Protection

To optimize the transient response and output voltage swing of

the BUF04, internal output short-circuit current limiting was

omitted. Although the BUF04 can provide continuous output

currents of 50 mA without protection, direct connection of the

BUF04’s output to ground or to the supplies will destroy the

device. An active current limit technique, illustrated in Figure

33, provides the necessary short-circuit protection while

retaining full dc output voltage swing to the load.

BUF04

7

6

10µF

0.1µF

0.1µF

–15V

10µF

4

3

+15V

RSC2

≥10Ω

2N2219

2N2219

2N2905

2N2905

RSC1

≥10Ω

0.01µF

SET ISC +(ISC–) <60mA,

CONTINUOUS

RSC1 (RSC2) =

0.6V

ISC + (ISC–)

6.2k

Ω

Figure 33. Short-Circuit Current Limiting Using

Current Sources