ADA4625-1ARDZ-R7 datasheet(21/30 Pages) AD

21 / 30 page

Data Sheet

ADA4625-1

Rev. 0 | Page 21 of 30

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 control the input at all times. Even though the

RRO of the ADA4625-1 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 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 68 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 68. 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 69 and Figure 70 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 turn off of ITAIL.

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 69. 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 70. ISY vs VCM, VSY = 5 V

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