ADA4625-1ARDZ-R7 datasheet(24/35 Pages) AD

24 / 35 page

ADA4625-1/ADA4625-2

Data Sheet

Rev. A | Page 24 of 35

NO PHASE INVERSION

Rail-to-rail output (RRO) amplifiers without rail-to-rail input

(RRI) are prone to phase inversion because the output can drive

the input outside of the normal common-mode range, causing

the output to go in the wrong direction and latch up. To prevent

phase inversion, the input must control the input at all times.

Even though the RRO of the ADA4625-1/ADA4625-2 input

stage (M1, M2, R1, and R2) operates correctly down to 0.2 V

below V−, it does not operate correctly within 2.5 V of V+. The

ADA4625-1/ADA4625-2 guarantees no phase inversion by

implementing an input pair (M3 and M4) to extend the

common-mode range to 0.2 V above V+, with reduced

performance. M3 and M4 are not active in the normal

common-mode range. Figure 88 shows that the input voltage

exceeds both supplies by 200 mV with no phase inversion at the

output.

–25

–20

–15

–10

–5

TIME (200µs/DIV)

VIN

VOUT

VSY = ±18V

VIN = 36.4V p-p

AV = 1

Figure 88. No Phase Reversal if the Input Range Exceeds the Power Supply

by 200 mV

SUPPLY CURRENT

The supply current (ISY) is the quiescent current drawn by the

op amp with no load. Figure 89 and Figure 90 show that the

quiescent current varies with the common-mode input voltage.

The shape of ISY vs. VCM at higher VCM shows saturation of

BUFF1 and the ITAIL turn off.

2.0

2.5

3.0

3.5

4.0

4.5

5.0

–18.2

–12.2

–6.2

–0.2

5.8

11.8

17.8

VCM (V)

TA = +85°C

TA = +25°C

TA = +125°C

TA = –40°C

Figure 89. ISY vs. VCM, VSY = ±18 V

2.0

2.5

3.0

3.5

4.0

4.5

5.0

–0.2

0.7

1.6

2.5

3.4

4.3

5.2

VCM (V)

TA = +85°C

TA = +25°C

TA = +125°C

TA = –40°C

Figure 90. ISY vs. VCM, VSY = 5 V

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