AD8531ART Analog Devices, AD8531ART Datasheet - Page 11

• Manufacturer Part Number: AD8531ART
• Description: Low Cost, 250 ma Output Single-supply Amplifiers
• Manufacturer: Analog Devices

REV. B
A High Output Current, Buffered Reference/Regulator
Many applications require stable voltage outputs relatively close
in potential to an unregulated input source. This “low drop-
out” type of reference/regulator is readily implemented with a
rail-to-rail output op amp, and is particularly useful when using
a higher current device such as the AD8531/AD8532/AD8534.
A typical example is the 3.3 V or 4.5 V reference voltage devel-
oped from a 5 V system source. Generating these voltages
requires a three terminal reference, such as the REF196 (3.3 V)
or the REF194 (4.5 V), both which feature low power, with
sourcing outputs of 30 mA or less. Figure 38 shows how such a
reference can be outfitted with an AD8531/AD8532/AD8534
buffer for higher currents and/or voltage levels, plus sink and
source load capability.
The low dropout performance of this circuit is provided by
stage U2, an AD8531 connected as a follower/buffer for the basic
reference voltage produced by U1. The low voltage saturation
characteristic of the AD8531/AD8532/AD8534 allows up to
100 mA of load current in the illustrated use, as a 5 V to 3.3 V
converter with good dc accuracy. In fact, the dc output voltage
change for a 100 mA load current delta measured less than
1 mV. This corresponds to an equivalent output impedance of
< 0.01 . In this application, the stable 3.3 V from U1 is ap-
plied to U2 through a noise filter, R1–C1. U2 replicates the U1
voltage within a few millivolts, but at a higher current output at
V
—unlike most IC references. R2 and C2 in the feedback path of
U2 provide additional noise filtering.
Transient performance of the reference/regulator for a 100 mA
step change in load current is also quite good and is largely
determined by the R5–C5 output network. With values as
shown, the transient is about 20 mV peak and settles to within
2 mV in less than 10 s for either polarity. Although room exists
for optimizing the transient response, any changes to the R5–C5
network should be verified by experiment to preclude the possi-
bility of excessive ringing with some capacitor types.
COMMON
ON/OFF
CONTROL
INPUT CMOS HI
(OR OPEN) = ON
LO = OFF
OUT1
Figure 38. A High Output Current Reference/Regulator
+V
+5V
V
S
V
S
C
, with the ability to both sink and source output current(s)
0.1 F
C3
3
0.1 F
REF196
C1
U1
2
4
6
V
OUT2
3.3V
=
(SeeText)
R1
10k
1%
C4
1 F
R3
R4
3.3k
10k
U2
AD8531
0.1 F
R2
C2
1%
3.3V @ 100mA
R5
0.2
C5
100 F/16V
TANTALUM
V
V
COMMON
OUT1
OUT
=
–11–
To scale V
resistor R3 (shown dotted) is added, causing, the new V
become:
The circuit can either be used as shown, as a 5 V to 3.3 V
reference/regulator, or with ON/OFF control. By driving Pin 3
of U1 with a logic control signal as noted, the output is switched
ON/OFF. Note that when ON/OFF control is used, resistor R4
must be used with U1 to speed ON-OFF switching.
A Single-Supply, Balanced Line Driver
The circuit in Figure 39 is a unique line driver circuit topology
used in professional audio applications and has been modified
for automotive and multimedia audio applications. On a single
+5 V supply, the line driver exhibits less than 0.7% distortion
into a 600
input signal level of 4 V p-p. In fact, the output drive capability
of the AD8531/AD8532/AD8534 maintains this level for loads
as small as 32 . For input signals less than 1 V p-p, the THD
is less than 0.1%, regardless of load. The design is a transformer-
less, balanced transmission system where output common-mode
rejection of noise is of paramount importance. As with the
transformer-based system, either output can be shorted to
ground for unbalanced line driver applications without changing
the circuit gain of 1. Other circuit gains can be set according to
the equation in the diagram. This allows the design to be easily
configured for inverting, noninverting or differential operation.
V
IN
SET: R7, R10, R11 = R2
SET: R6, R12, R13 = R3
A1, A2 = 1/2 AD8532
GAIN =
Figure 39. A Single-Supply, Balanced Line Driver for
Multimedia and Automotive Applications
22 F
C1
R3
R2
OUT2
2
3
load from 20 Hz to 15 kHz (not shown) with an
+5V
A1
to another (higher) output level, the optional
10k
10k
10k
R1
V
R10
1
R2
OUT 1
AD8531/AD8532/AD8534
R11
10k
2
3
R7
10k
5
6
V
OUT 2
A2
A2
10k
R3
7
10k
R12
+12V
10k
R13
1
7
A1
1
100k
6
5
10k
R6
R9
R2
R3
+5V
R14
50
50
R5
R8
100k
1 F
C2
47 F
47 F
C3
C4
600
OUT1
R
L
to
V
V
O1
O2