MAX4412/MAX4413
Low-Cost, Low-Power, Ultra-Small, 3V/5V, 500MHz
Single-Supply Op Amps with Rail-to-Rail Outputs
_______________________________________________________________________________________ 9
Detailed Description
The MAX4412/MAX4413 single-supply, rail-to-rail, volt-
age-feedback amplifiers achieve 140V/µs slew rates
and 500MHz -3dB bandwidths, while consuming only
1.7mA of supply current per amplifier. Excellent har-
monic distortion and differential gain/phase perfor-
mance make these amplifiers an ideal choice for a wide
variety of video and RF signal-processing applications.
Internal feedback around the output stage ensures low
open-loop output impedance, reducing gain sensitivity
to load variations. This feedback also produces
demand-driven current bias to the output transistors.
Rail-to-Rail Outputs,
Ground-Sensing Input
The MAX4412/MAX4413 input common-mode range
extends from (V
EE
- 0.1V) to (V
CC
- 1.5V) with excellent
common-mode rejection. Beyond this range, the ampli-
fier output is a nonlinear function of the input, but does
not undergo phase reversal or latchup.
The output swings to within 105mV of either power-sup-
ply rail with a 1kΩ load. Input ground sensing and rail-
to-rail outputs substantially increase the dynamic
range. With a symmetric input in a single +5V applica-
tion, the input can swing 3.6Vp-p, and the output can
swing 4.6Vp-p with minimal distortion.
Output Capacitive Loading
and Stability
The MAX4412/MAX4413 are optimized for AC perfor-
mance. They are not designed to drive highly reactive
loads. Such loads decrease phase margin and may
produce excessive ringing and oscillation. The use of
an isolation resistor eliminates this problem (Figure 1).
Figure 2 is a graph of the Optimal Isolation Resistor
(R
ISO
) vs. Capacitive Load.
The Small Signal Gain vs. Frequency with Capacitive
Load and No Isolation Resistor graph in the
Typical
Operating Characteristics
shows how a capacitive load
causes excessive peaking of the amplifier’s frequency
response if the capacitor is not isolated from the ampli-
fier by a resistor. A small isolation resistor (usually 20Ω
to 30Ω) placed before the reactive load prevents ring-
ing and oscillation. At higher capacitive loads, AC per-
formance is controlled by the interaction of the load
capacitance and the isolation resistor. The Small-Signal
Gain vs. Frequency with Capacitive Load and 22Ω
Isolation Resistor graph shows the effect of a 22Ω isola-
tion resistor on closed-loop response.
Coaxial cable and other transmission lines are easily
driven when properly terminated at both ends with their
characteristic impedance. Driving back-terminated
transmission lines essentially eliminates the line’s
capacitance.
___________Applications Information
Choosing Resistor Values
Unity-Gain Configuration
The MAX4412/MAX4413 are internally compensated for
unity gain. When configured for unity gain, the devices
require a 24Ω feedback resistor (R
F
). This resistor
improves AC response by reducing the Q of the paral-
lel LC circuit formed by the parasitic feedback capaci-
tance and inductance.
Pin Description
