ADHV4702-1BCPZ-R7 datasheet(14/22 Pages) AD

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Data Sheet

ADHV4702-1

THEORY OF OPERATION

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Rev. D | 14 of 22

Figure 44. Functional Block Diagram

The ADHV4702-1 is a high voltage (220 V) precision amplifier

designed using the next generation of proprietary bipolar/ comple-

mentary metal-oxide semiconductor (CMOS)/laterally diffused met-

al-oxide semiconductor (BCDMOS) process from Analog Devices.

Figure 44 shows the functional block diagram. The input stage

architecture offers the advantages of high input impedance with

low input bias current, low input offset voltage, low drift, and low

noise for precision demanding applications, such as automated test

equipment (ATE).

INTERNAL ELECTROSTATIC DISCHARGE

(ESD) PROTECTION

As shown in Figure 45, the ADHV4702-1 has an internal ESD

configuration to prevent damage due to overvoltage. The ESD pro-

tection circuitry involves current steering diodes connected from the

input and output pins to the power supply rails. The ADHV4702-1

also includes internal input clamping diodes across the inverting

and noninverting inputs to prevent large differential input voltages

from damaging the input stage transistors. This input clamping

circuit greatly reduces the input impedance for differential input vol-

tages greater than the forward-biased voltage (VF) of four diodes.

The ESD protection circuitry remains inactive under normal opera-

tion. To avoid forward biasing the ESD diodes, do not overdrive

the pin voltages above the absolute maximum ratings, and ensure

that the input differential voltage does not exceed 4 VF. Additional

external input clamping diodes may be required to protect the slew

boost circuit. See the Slew Boost Circuit and Protection section.

Figure 45. Simplified ESD Configuration

SLEW BOOST CIRCUIT AND PROTECTION

The ADHV4702-1 uses a supplementary slew boosting circuit to

achieve its typical slew rate of 74 V/µs across a 200 V p-p output

range at unity gain. This slew boosting circuit works by sensing the

differential input voltage of the amplifier and converting this voltage

into a dynamic current to help drive capacitances within the signal

path of the amplifier. With greater input voltage across the inputs,

more dynamic current is produced, which enables the amplifier

to slew faster. The current produced by the slew boosting circuit

transmits to all stages of the amplifier during slewing.

Internally, the ADHV4702-1 contains differential input voltage

clamps that limit transient differential signals to 4 VF, placing an

upper limit on the slew boost. Large differential input voltages

(which can be occur with signal frequencies approaching the full

power bandwidth) trigger the slew boosting circuit, resulting in an

increased dynamic supply current. The relationship between slew

rate and full power bandwidth (fM) is given in the following equation:

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