MAX4238 Maxim, MAX4238 Datasheet - Page 7

• Manufacturer Part Number: MAX4238
• Description: The MAX4238/MAX4239 are low-noise, low-drift, ultra-high precision amplifiers that offer near-zero DC offset and drift through the use of autocorrelating zeroing techniques
• Manufacturer: Maxim

The MAX4238/MAX4239 are high-precision amplifiers
that have less than 2.5µV of input-referred offset and
low 1/f noise. These characteristics are achieved
through a patented autozeroing technique that samples
and cancels the input offset and noise of the amplifier.
The pseudorandom clock frequency varies from 10kHz
to 15kHz, reducing intermodulation distortion present in
chopper-stabilized amplifiers.
(V
TDFN SOT23
CC
—
—
1
2
3
4
5
6
= 5V, V CM = 0V, R
PIN
—
—
1
2
3
4
5
6
OUT
5, 8
SO
—
V
V
6
4
3
2
1
7
CC
EE
_______________________________________________________________________________________
= -2.5V
= 2.5V
L
NAME
Detailed Description
GND
OUT
N.C.
= 10kΩ connected to V
IN+
V
IN-
EP
CC
DC TO 10Hz NOISE
Ground
Shutdown Input. Active-low
shutdown, connect to V
for normal operation.
Positive Power Supply
No Connection. Not
internally connected.
Exposed Pad (TDFN only).
Connect EP to GND.
Amplifier Output
Noninverting Input
Inverting Input
1s/div
Pin Description
Ultra-Low Offset/Drift, Low-Noise,
FUNCTION
MAX4238/39 toc19
Typical Operating Characteristics (continued)
CC
/2, SHDN = V
2µV/div
Precision SOT23 Amplifiers
CC
CC
, T
To achieve very low offset, several sources of error
common to autozero-type amplifiers need to be consid-
ered. The first contributor is the settling of the sampling
capacitor. This type of error is independent of input-
source impedance, or the size of the external gain-set-
ting resistors. Maxim uses a patented design technique
to avoid large changes in the voltage on the sampling
capacitor to reduce settling time errors.
The second error contributor, which is present in both
autozero and chopper-type amplifiers, is the charge
injection from the switches. The charge injection
appears as current spikes at the input, and combined
with the impedance seen at the amplifier’s input, con-
tributes to input offset voltage. Minimize this
feedthrough by reducing the size of the gain-setting
resistors and the input-source impedance. A capacitor
in parallel with the feedback resistor reduces the
amount of clock feedthrough to the output by limiting
the closed-loop bandwidth of the device.
The design of the MAX4238/MAX4239 minimizes the
effects of settling and charge injection to allow specifi-
cation of an input offset voltage of 0.1µV (typ) and less
than 2.5µV over temperature (-40°C to +85°C).
1/f noise, inherent in all semiconductor devices, is
inversely proportional to frequency. 1/f noise increases
3dB/octave and dominates amplifier noise at lower fre-
quencies. This noise appears as a constantly changing
voltage in series with any signal being measured. The
MAX4238/MAX4239 treat 1/f noise as a slow varying
offset error, inherently canceling the 1/f noise.
A
= +25°C, unless otherwise noted.)
SHDN
OUT
R
C
L
L
= 10kΩ
= 100pF
SHUTDOWN WAVEFORM
10µs/div
Offset Error Sources
MAX4238/39 toc20
2V/div
1V/div
1/f Noise
7