MAX4247 Maxim, MAX4247 Datasheet - Page 8

• Manufacturer Part Number: MAX4247
• Description: The MAX4245/MAX4246/MAX4247 family of low-cost op amps offer rail-to-rail inputs and outputs, draw only 320µA of quiescent current, and operate from a single +2
• Manufacturer: Maxim

input resistance is typically 4MΩ. For differential volt-
ages greater than 2.1V, input resistance is around
10.6kΩ, and the input bias current can be approximat-
ed by the following equation:
In the region where the differential input voltage
approaches 2.1V, the input resistance decreases expo-
nentially from 4MΩ to 10.6kΩ as the diodes begin to
conduct. It follows that the bias current increases with
the same curve.
In unity-gain configuration, high slew-rate input signals
may capacitively couple to the output through the
triple-diode stacks.
The MAX4245/MAX4246/MAX4247 can drive a 2kΩ
load and still typically swing within 35mV of the supply
rails. Figure 3 shows the output voltage swing of the
MAX4245 configured with A
The MAX4245/MAX4246/MAX4247 operate from a sin-
gle +2.5V to +5.5V supply (or dual ±1.25V to ±2.75V
supplies) and consume only 320µA of supply current
per amplifier. A 90dB power-supply rejection ratio
allows the amplifiers to be powered directly off a
decaying battery voltage, simplifying design and
extending battery life.
The MAX4245/MAX4246/MAX4247 output typically set-
tles within 4µs after power-up. Figure 4 shows the out-
put voltage on power-up and power-down.
The MAX4245/MAX4247 feature a low-power shutdown
mode. When SHDN_ is pulled low, the supply current
drops to 50nA per amplifier, the amplifier is disabled,
and the output enters a high-impedance state. Pulling
Ultra-Small, Rail-to-Rail I/O with Disable,
Single-/Dual-Supply, Low-Power Op Amps
Figure 2. Input Protection Circuit
8
IN+
IN-
_______________________________________________________________________________________
5.3kΩ
5.3kΩ
I
B
Applications Information
= (V
Power-Supply Considerations
DIFF
Rail-to-Rail Output Stage
- 2.1V) / 10.6kΩ
V
= -1V/V.
Shutdown Mode
Power-Up
SHDN_ high enables the amplifier. Figure 5 shows the
MAX4245/MAX4247’s shutdown waveform.
Due to the output leakage currents of three-state
devices and the small internal pullup current for SHDN_,
do not leave SHDN_ open/high-impedance. Leaving
SHDN_ open may result in indeterminate logic levels,
and could adversely affect op amp operation. The logic
threshold for SHDN_ is referred to V
supplies, pull SHDN_ to V
op amp.
The MAX4245/MAX4246/MAX4247 are unity-gain stable
for loads up to 470pF. Applications that require greater
capacitive drive capability should use an isolation
resistor between the output and the capacitive load
Figure 3. Rail-to-Rail Input/Output Voltage Range
Figure 4. Power-Up/Power-Down Waveform
OUT
OUT
V
DD
IN
Driving Capacitive Loads
400µs/div
10µs/div
SS
, not GND, to shut down the
SS
. When using dual
2V/div
2V/div
2V/div
2V/div