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ADA4800ACPZ-R7

P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17
ADA4800
Rev. A | Page 9 of 16
TEST CIRCUIT
ADA4800
I
AL
I
BUFF
+1
I
DRV
I
SF
6
ISF
1
IN
5
VCC
2
VEE
4
IDRV
3
OUT
R
ISF
10kΩ
3V
V
ISF
0.11mA
R
IDRV
249kΩ
15V
0.05mA
7.5V
49.9Ω
2.96mA
7.5V
4.68mA
1.41mA
09162-026
0.1µF
10µF
+
1kΩ10Ω
22pF
Figure 20. Typical Current Flow
ADA4800
Rev. A | Page 10 of 16
THEORY OF OPERATION
The ADA4800 is a buffer integrated with an active load. Each
element (the active load and the buffer) operates independently,
as described in the following sections.
Figure 22 illustrates an ADA4800 application configuration for
using this power save feature.
An external resistor connected between the ISF and the
microcontroller GPO pin determines the amount of current
that flows into the input pin. This current can be calculated
by using Equation 1 and Equation 2.
SETTING ACTIVE LOAD CURRENT WITH PIN 6 (ISF)
The ISF pin is used to establish the value of the active current
load (I
AL
). Set the ISF current using Equation 1.
k3
V55.1
+
−
=
ISF
ISF
ISF
R
V
I
(1)
SETTING BANDWIDTH WITH PIN 4 (IDRV)
The IDRV pin establishes the buffer’s I
CC
quiescent current.
As I
CC
is increased, power dissipation and bandwidth both
increase. Set the current using Equation 3.
where:
V
ISF
is referenced to Pin 2. V
ISF
can be an external voltage source,
V
CC
, or a GPO output as explained in the following paragraphs.
R
ISF
is the external resistor between the ISF pin and V
ISF
.
k28
V8.0
+
−
=
IDRV
IDRV
IDRV
R
V
I
(3)
where:
V
IDRV
is referenced to Pin 2. V
IDRV
can be an external voltage
source or V
CC
.
R
IDRV
is the external resistor between the IDRV pin and V
IDRV
.
The active load current (into the IN pin) is directly proportional
to I
ISF
and can be calculated by Equation 2.
I
AL
= I
ISF
× 27 (2)
The ADA4800 allows for additional power savings by reducing
the active load current. The active load current can be logically
controlled by connecting the ISF pin to any general-purpose
output (GPO) pin of a system microcontroller through an
external resistor. A GPO logic high enables the flow of the
active load current. Appling –V
S
or connecting a high-Z to the
ISF pin places the ADA4800 into power save mode by shutting
down the active load current.
The I
CC
current is directly proportional to I
IDRV
and can be
calculated by Equation 4.
I
CC
= I
IDRV
× 26 (4)
Applying –V
S
to the IDRV pin shuts down the buffer.
ADA4800
Rev. A | Page 11 of 16
APPLICATIONS INFORMATION
OPEN SOURCE CCD OUTPUT BUFFER
With low power, high slew rate, and fast settling time, the
ADA4800 is the ideal solution for an output buffer for CCD
sensors with an open source output configuration. Figure 21
shows a typical application circuit for the ADA4800 as a CCD
sensor output buffer.
The output of the CCD is connected directly to the IN pin
of the ADA4800, whose OUT pin is then ac-coupled into
the input of the analog front end.
IN VEE OUT
CCD
AFE
09162-027
15V
ADA4800
I
AL
I
BUFF
+1
I
IDRV
I
ISF
6
ISF
1
5
VCC
2
4
IDRV
3
R
ISF
120kΩ
15V
V
ISF
R
IDRV
249kΩ
0.1µF
0.1µF
0.1µF
47µF
+
Figure 21. Typical Application Block Diagram
To help reduce the effects of power supply noise coupling into
the ISF and IDRV pins, use 0.1 F ceramic bypass decoupling
capacitors. For best performance, place these capacitors as
close to each of these pins as is physically possible.
POWER SAVE MODE
The buffer of the ADA4800 consumes only 20 mW of static
power. To achieve even more power savings, the ADA4800
active load current can be switched off during standby mode
or reduced during monitoring mode. Figure 22 illustrates the
ADA4800 as an open source CCD buffer configured for using
this power save feature. Power save mode allows I
AL
current to
be logically controlled by connecting the ISF pin to any general-
purpose output (GPO) pin of the system microcontroller through
an external resistor. A GPO logic high enables the flow of input
sink current, while a logic low disables the input sink current
and asserts the power save mode.
0V TO 3V
GPO PIN
IN VEE OUT
CCD
AFE
09162-028
15V
ADA4800
I
AL
I
BUFF
+1
I
IDRV
I
ISF
6
ISF
1
5
VCC
2
4
IDRV
3
R
ISF
10kΩ
V
ISF
R
IDRV
249kΩ
0.1µF
0.1µF
0.1µF
47µF
+
Figure 22. Using GPO to Drive ISF Voltage
Figure 23 shows an example of the ADA4800 power save feature.
AFE
GPO1
GPO2
20kΩ
20kΩ
MAIN BOARD FPC
ADA4800
ISF
09162-029
Figure 23. Example Block Diagram for Sink Current Selection
Three combinations of I
AL
are provided with Figure 23.
Selection of the I
AL
is controlled by the logic signals applied to
the GPO1 and GPO2 pins. Table 5 summarizes the I
AL
selections.
Table 5. Input Sink Current Selection
Mode GPO1 GPO2 Resistance (kΩ) Active Load Current, I
AL
(mA)
Standby High-Z High-Z High-Z 0
0 0 N/A
Sleep High-Z 1 20 1.90
1 High-Z 20
Active 1 1 10 3.36
P1-P3P4-P6P7-P9P10-P12P13-P15P16-P17

ADA4800ACPZ-R7

Mfr. #:
Buy ADA4800ACPZ-R7
Manufacturer:
Analog Devices Inc.
Description:
High Speed Operational Amplifiers Low Power High Spd CCD Buffer
Lifecycle:
New from this manufacturer.
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