OP484 datasheet(15/20 Pages) AD

Part #	OP484

Description	Precision Rail-to-Rail Input & Output Operational Amplifiers

Download	20 Pages

Scroll/Zoom	100%

Manufacturer	AD [Analog Devices]

Direct Link	http://www.analog.com

Logo

15 / 20 page

REV. 0

–15–

OP184/OP284/OP484

10

0%

100

90

1nF LOAD

ONLY

SNUBBER

IN

CIRCUIT

2µs

50mv

µs

Figure 54. Overshoot and Ringing Is Reduced by Adding a

“Snubber” Network in Parallel with the 1 nF Load

Table I. Snubber Networks for Large Capacitive Loads

Load Capacitance

Snubber Network

(CL)(RS, CS)

1 nF

50

Ω, 100 nF

10 nF

20

Ω, 1 µF

100 nF

5

Ω, 10 µF

A Low Dropout Regulator with Current Limiting

Many circuits require stable regulated voltages relatively close in

potential to an unregulated input source. This “low dropout”

type of regulator is readily implemented with a rail-to-rail out-

put op amp such as the OP284, because the wide output swing

allows easy drive to a low saturation voltage pass device. Fur-

thermore, it is particularly useful when the op amp also enjoys a

rail-rail input feature, as this factor allows it to perform high-

side current sensing for positive rail current limiting. Typical ex-

amples are voltages developed from 3 V to 9 V range system

sources, or anywhere where low dropout performance is required

for power efficiency. The 4.5 V case here works from 5 V nomi-

nal sources, with worst-case levels down to 4.6 V or less.

Figure 55 shows such a regulator set up using an OP284 plus a

low RDS(ON), P-channel MOSFET pass device. Part of the low

dropout performance of this circuit is provided by Q1, which

has a rating of 0.11

Ω with a gate drive voltage of only 2.7 V.

This relatively low gate drive threshold allows operation of the

regulator on supplies as low as 3 V without compromise to over-

all performance.

The circuit’s main voltage control loop operation is provided by

U1B, half of the OP284. This voltage control amplifier ampli-

fies the 2.5 V reference voltage produced by three terminal U2,

a REF192. The regulated output voltage VOUT is then:

VOUT =VOUT 2 1 +

R2

R 3

()

For the example here, a VOUT of 4.5 V with VOUT2 = 2.5 V re-

quires a U1B gain of 1.8 times, so R3 and R2 are chosen for a

ratio of 1.2:1, or 10.0 k

Ω:8.06 kΩ (using closest 1% values).

Note that for the lowest VOUT dc error, R2 R3 should be main-

tained equal to R1 (as here), and the R2-R3 resistors should be

stable, close tolerance metal film types. The table in Figure 55

summarizes R1-R3 values for some popular voltages. However,

note that in general the output can be anywhere between VOUT2

to the 12 V maximum rating of Q1.

While the low voltage saturation characteristic of Q1 is a key

part of the low dropout, another component is a low current

sense comparison threshold with good dc accuracy. Here, this

is provided by current sense amplifier U1A, which is provided a

20 mV reference from the 1.235 V AD589 reference diode D2

and the R7-R8 divider. When the product of the output current

and the RS value matches this voltage threshold, the current

control loop is activated, and U1A drives Q1’s gate through D1.

This causes the overall circuit operation to enter current mode

control, with a current limit ILIMIT defined as:

ILIMIT =

VR(D2)

RS









R7

+ R8

()

R9

27.4k

Ω

C4

0.1µF

C5

0.01µF

R11

1k

Ω

R6

4.99k

Ω

R8

301k

Ω

+VS

R10

1k

Ω

R2

8.06k

Ω

C3

0.1µF

RS

0.05

Ω

C6

10µF

3

2

1

8

4

R7

4.99k

Ω

U1A

OP284

D2

AD589

D1

1N4148

R5

22.1k

Ω

Q1

SI9433DY

R4

2.21k

Ω

6

5

7

C1

0.01µF

U1B

OP284

D3

1N4148

2

6

4

3

U2

REF192

C2

1µF

R1

4.53k

Ω

VOUT2

2.5V

R3

10k

Ω

5.0V

4.5V

3.3V

3.0V

4.99k

4.53k

2.43k

1.69k

10.0k

8.06k

3.24k

2.00k

10.0k

VOUT R1

R2

R3

OUTPUT TABLE

VS > VOUT + 0.1V

OPTIONAL

ON/OFF CONTROL INPUT

CMOS HI (OR OPEN) = ON

LO = OFF

VIN COMMON

VC

VOUT =

4.5V @ 350mA

(SEE TABLE)

VOUT COMMON

Figure 55. A Low Dropout Regulator with Current Limiting

Similar Part No. - OP484

Manufacturer	Part #	Datasheet	Description
Analog Devices	OP484	522Kb / 20P	Precision Rail-to-Rail Input & Output Operational Amplifiers REV. 0
	OP484	508Kb / 24P	Precision Rail-to-Rail Input and Output Operational Amplifiers REV. D
	OP484EP	522Kb / 20P	Precision Rail-to-Rail Input & Output Operational Amplifiers REV. 0
	OP484ES	522Kb / 20P	Precision Rail-to-Rail Input & Output Operational Amplifiers REV. 0
	OP484ES	508Kb / 24P	Precision Rail-to-Rail Input and Output Operational Amplifiers REV. D

More results

Similar Description - OP484

Manufacturer	Part #	Datasheet	Description
Analog Devices	OP-184	522Kb / 20P	Precision Rail-to-Rail Input & Output Operational Amplifiers REV. 0
	OP184	508Kb / 24P	Precision Rail-to-Rail Input and Output Operational Amplifiers REV. D
	OP284	676Kb / 24P	Precision Rail-to-Rail Input and Output Operational Amplifiers
	OP184	676Kb / 24P	Precision Rail-to-Rail Input and Output Operational Amplifiers
	OP484	676Kb / 24P	Precision Rail-to-Rail Input and Output Operational Amplifiers
	AD8605ARTZ	836Kb / 24P	Precision, Low Noise, CMOS, Rail-to-Rail, Input/Output Operational Amplifiers Rev. N
	AD8605	559Kb / 20P	Precision Low noise CMOS Rail-to-Rail Input/Output Operational Amplifiers REV. D
	AD8605	738Kb / 24P	Precision, Low Noise, CMOS, Rail-to-Rail, Input/Output Operational Amplifiers Rev. H
	AD8615	403Kb / 20P	Precision, 20 MHz, CMOS, Rail-to-Rail Input/Output Operational Amplifiers Rev. C
	AD8615	190Kb / 5P	Precision 20 MHz CMOS Rail-to-Rail Input/Output Operational Amplifiers REV. PrA

More results

OP484 Datasheet(PDF) 15 Page - Analog Devices

OP484 Datasheet(HTML) 15 Page - Analog Devices

Similar Part No. - OP484

Similar Description - OP484

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL