MAX477ESA Maxim Integrated Products, MAX477ESA Datasheet - Page 8

• Manufacturer Part Number: MAX477ESA
• Description: Op Amps
• Manufacturer: Maxim Integrated Products

Specifications of MAX477ESA

• Number Of Channels: 1
• Voltage Gain Db: 65 dB
• Common Mode Rejection Ratio (min): 70 dB
• Input Offset Voltage: 2 mV
• Maximum Power Dissipation: 471 mW
• Maximum Operating Temperature: + 85 C
• Mounting Style: SMD/SMT
• Package / Case: SOIC-8 Narrow
• Minimum Operating Temperature: - 40 C

300MHz High-Speed Op Amp
Figure 2. Effect of High-Feedback Resistor Values and
Parasitic Capacitance on Bandwidth
The MAX477 can be configured as an inverting or non-
inverting gain block in the same manner as any other
voltage-feedback op amp. The gain is determined by
the ratio of two resistors and does not affect amplifier
frequency compensation. This is unlike CMF op amps,
which have a limited range of feedback resistors, typi-
cally one resistor value for each gain and load setting.
This is because the -3dB bandwidth of a CMF op amp
is set by the feedback and load resistors. Figure 1a
shows the inverting gain configuration and its gain
equation, while Figure 1b shows the noninverting gain
configuration.
The feedback and input resistor values are not critical
in the inverting or noninverting gain configurations (as
with current-feedback amplifiers). However, be sure to
select resistors that are small and noninductive.
Surface-mount resistors are best for high-frequency cir-
cuits. Their material is similar to that of metal-film resis-
tors, but to minimize inductance, it is deposited in a flat,
linear manner using a thick film. Their small size and
lack of leads also minimize parasitic inductance and
capacitance.
The MAX477’s input capacitance is approximately 1pF.
In either the inverting or noninverting configuration,
excess phase resulting from the pole frequency formed
by R
and cause oscillations (Figure 2). Table 1 shows the
recommended resistor combinations and measured
bandwidth for several gain values.
The standard voltage-feedback topology of the
MAX477 allows DC error and noise calculations to be
done in the usual way. The following analysis shows
8
_______________________________________________________________________________________
f
V
IN
R
g
and C can degrade amplifier phase margin
R
G
C
MAX477
Choosing Resistor Values
DC and Noise Errors
R
F
Setting Gain
R
L
V
OUT
that the MAX477’s voltage-feedback architecture pro-
vides a precision amplifier with significantly lower DC
errors and lower noise compared to CMF amplifiers.
1) In Figure 3, total output offset error is given by:
2) The MAX477’s total input-referred noise in a closed-
where e
Table 1. Resistor and Bandwidth Values for
Various Closed-Loop Gain Configurations
V
OUT
For the special case in which R
equal to R f
for I
drops out of the equation for total DC error. In prac-
tice, high-speed configurations for the MAX477
necessitate the use of low-value resistors for R
and Rg. In this case, the V
DC error source.
loop feedback configuration can be calculated by:
GAIN
(V/V)
+10
-10
+1
+2
+5
-1
-2
-5
= 1+
OS
i
R
e
n
n
R
V
EQ
e
OS
(R
T
R
= input-referred noise voltage of the
= input-referred noise current of the
= resistor noise voltage due to R
R
= total equivalent source resistance at
S
g
f
MAX477 (5nV √
MAX477 (2pA √ Hz)
the two inputs, i.e., R
||
I R
+ (R f
e
B S
R
Rg, the I
Open
e
500
125
300
150
100
(Ω)
=
R
50
50
–
n
g
||
2
I R
B
4KT R
Rg) << V
e
B
R
f
||
2
terms cancel out. Note also,
R
Hz)
EQ
g
OS
i R
n EQ
Short
500
500
450
300
300
500
500
(Ω)
OS
R
I
term is the dominant
f
OS
EQ
S
, the I
is arranged to be
2
R
= R
S
S
OS
BANDWIDTH
+ R
R
EQ
(MHz)
term also
f
-3dB
120
114
300
||
25
12
64
42
23
, i.e.,
f
||
R
S
g
R
, R
g
f
,