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參數(shù)資料
| 型號： | PB51A |
| 英文描述： | Operational Amplifier |
| 中文描述： | 運算放大器 |
| 文件頁數(shù)： | 4/4頁 |
| 文件大?。?/td> | 71K |
| 代理商： | PB51A |
APEX MICROTECHNOLOGY CORPORATION
5980 NORTH SHANNON ROAD TUCSON, ARIZONA 85741 USA APPLICATIONS HOTLINE: 1 (800) 546-2739
PB51U REV. A JULY 2001 2001 Apex Microtechnology Corp.
OPERATING
CONSIDERATIONS
PB51 PB51A
STABILITY
St
ability can be maximized by observing the following
guidelines:
1. Operate the booster in the lowest practical gain.
2. Operate the driver amplifier in the highest practical
effective gain.
3. Keep gain-bandwidth product of the driver lower than the
closed loop bandwidth of the booster.
4. Minimize phase shift within the loop.
A good compromise for (1) and (2) is to set booster gain
from 3 to 10 with total (composite) gain at least a factor of 3
times booster gain. Guideline (3) implies compensating the
driver as required in low composite gain configurations. Phase
shift within the loop (4) is minimized through use of booster
and loop compensation capacitors Cc and Cf when required.
Typical values are 5pF to 33pF.
Stability is the most difficult to achieve in a configuration where
driver effective gain is unity (ie; total gain = booster gain). For
this situation, Table 1 gives compensation values for optimum
square wave response with the op amp drivers listed.
SLEW RATE
Th
e slew rate of the composite amplifier is equal to the slew
rate of the driver times the booster gain, with a maximum
value equal to the booster slew rate.
OUTPUT SWING
Th
e maximum output voltage swing required from the driver
op amp is equal to the maximum output swing from the booster
divided by the booster gain. The Vos of the booster must also
be supplied by the driver, and should be subtracted from the
available swing range of the driver. Note also that effects of Vos
drift and booster gain accuracy should be considered when
calculating maximum available driver swing.
GENERAL
Please read Application Note 1 "General Operating
Considerations" which covers stability, supplies, heat sinking,
mounting, current limit, SOA interpretation, and specification
interpretation. Visit www.apexmicrotech.com for design tools
that help automate tasks such as calculations for stability,
internal power dissipation, current limit; heat sink selection;
Apex’s complete Application Notes library; Technical Seminar
Workbook; and Evaluation Kits.
CURRENT LIMIT
For proper operation, the current limit resistor (R
) must be
con nected as shown in the external connection diagram. The
minimum value is 0.33 with a maximum practical value of 47.
For optimum reliability the resistor value should be set as high
as possible. The value is calculated as follows:
+I
L
=.65/R
CL
+ .010, -I
L
= .65/R
CL
.
SAFE OPERATING AREA (SOA)
NOTE: The output stage is protected against transient flyback. However,
for protection against sustained, high energy flyback, external fast-recovery
diodes should be used.
COMPOSITE AMPLIFIER CONSIDERATIONS
Cascading two amplifiers within a feedback loop has many
advantages, but also requires careful consideration of several
amplifier and system parameters. The most important of these
are gain, stability, slew rate, and output swing of the driver.
Operating the booster amplifier in higher gains results in a
higher slew rate and lower output swing requirement for the
driver, but makes stability more difficult to achieve.
GAIN SET
The booster’s closed-loop gain is given by the equation
above. The composite amplifier’s closed loop gain is determined
by the feedback network, that is: –Rf/Ri (inverting) or 1+Rf/Ri
(non-inverting). The driver amplifier’s “effective gain” is equal to
the composite gain divided by the booster gain.
Example: Inverting configuration (figure 1) with
R i = 2K, R f = 60K, R g = 0 :
Av (booster) = (6.2K/3.1K) + 1 = 3
Av (composite) = 60K/2K = – 30
Av (driver) = – 30/3 = –10
t=100ms
seadysaeTc=25
°
C
°
C
seadyseadysaeTc=85
°
C
3
2
1
.2
.3
.4
.5
10
20
30 40 50
100
200 300
O
F
SUPPLY TO OUTPUT DIFFERENTIAL VOLTAGE, Vs –Vo (V)
.1
OP
AMP
PB51
C
F
R
F
R
I
+15V
–15V
IN
COM
+Vs
–Vs
R
CL
OUT
C
C
R
G
R
L
V
IN
GAIN
COMP
C
CH
FIGURE 2. NON-INVERTING COMPOSITE AMPLIFIER.
R
G
= [(Av-1) * 3.1K] - 6.2K
R
G
+ 6.2K
Av =
3.1K
+1
DRIVER
OP07
741
LF155
LF156
TL070
For: R
F
= 33K, R
I
= 3.3K, R
G
= 22K
TABLE 1. TYPICAL VALUES FOR CASE WHERE OP AMP
EFFECTIVE GAIN = 1.
C
CH
-
-
-
-
22p
C
F
22p
18p
4.7p
4.7p
15p
C
C
22p
10p
10p
10p
10p
FPBW
4kHz
20kHz
60kHz
80kHz
80kHz
SR
1.5
7
>60
>60
>60
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