ADHV4702-1BCPZ-R7 datasheet(16/22 Pages) AD

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Data Sheet

ADHV4702-1

THEORY OF OPERATION

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Rev. D | 16 of 22

DIGITAL GROUND (DGND)

DGND is the reference for all low voltage pins of the amplifier

(RADJ, TMP, and SD) and serves as a signal ground for communica-

tion to a microprocessor or other low voltage logic circuit. Connect

DGND to a 0 V digital ground or analog ground. Do not float DGND.

RESISTOR ADJUSTABLE QUIESCENT

CURRENT (RADJ)

To reduce further power consumption, the quiescent current of the

ADHV4702-1 can be adjusted by placing a resistor (RADJ) between

the RADJ pin and DGND.

To fully bias the amplifier, short the RADJ pin directly to DGND to

allow maximum dynamic performance. To bias the amplifier with

minimum quiescent power consumption, place a 100 kΩ resistor

from RADJ to DGND. This resistor reduces quiescent supply cur-

rent to approximately 0.6 mA. Operating the amplifier at a lower

quiescent current has minimal effect on dc performance but can

result in an associated reduction in dynamic performance, such

as bandwidth and noise. Figure 51 and Figure 52 show the small

signal frequency response and noise performance at various RADJ

values.

Figure 51. Small Signal Frequency Response at Various RADJ, TA = 25°C, AV =

1, VS = ±110 V, VOUT = 100 mV p-p, RF = 0 Ω, RLOAD = 10 kΩ

Figure 52. Input Voltage Noise at Various RADJ, TA = 25°C, VS = ±110 V

SHUTDOWN PIN (SD)

The ADHV4702-1 is equipped with a power saving shutdown fea-

ture. When the SD pin voltage is brought low to within 0.8 V of

DGND, the amplifier is disabled and put in a low power state,

reducing its quiescent current to approximately 0.18 mA. The SD

pin has an internal approximately 400 kΩ pull-up resistor that

enables the amplifier if SD is left floating. When turning the amplifier

on from the shutdown state, pull the SD pin high to at least 1.6

V above the DGND pin. The SD pin response time for starting up

and coming out of shutdown is shown in Figure 53 and Figure 54.

The SD pin can support digital logic levels down to 2.5 V. The SD

pin can be used to implement thermal shutdown and short-circuit

protection when used in conjunction with the temperature monitor

feature of the ADHV4702-1.

Figure 53. SD Pin Response Time, Turning On

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