MAX4004EUT+T Maxim Integrated Products, MAX4004EUT+T Datasheet - Page 8

• Manufacturer Part Number: MAX4004EUT+T
• Description: IC CURRENT MONITOR 5% SOT23-6
• Manufacturer: Maxim Integrated Products

Specifications of MAX4004EUT+T

• Function: Current Monitor
• Sensing Method: High-Side
• Accuracy: ±5%
• Voltage - Input: 2.7 ~ 22 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: SOT-23-6
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• Other names: MAX4004EUT+T; MAX4004EUT+TTR

In many fiber applications, OUT is connected directly to
an ADC that operates from a supply voltage that is less
than the voltage at BIAS. Connecting the
MAX4004/MAX4006’s clamping diode output, CLAMP,
to the ADC power supply helps avoid damage to the
ADC. Without this protection, voltages can develop at
OUT that can destroy the ADC. This protection is less
critical when OUT is connected directly to subsequent
transimpedance amplifiers (linear or logarithmic) that
have low-impedance, near-ground-referenced inputs. If
a transimpedance amp is used on the low side of the
photodiode, its voltage drop must also be considered.
Leakage from the clamping diode is most often insignif-
icant over nominal operating conditions, but grows with
temperature.
To maintain low levels of wideband noise, lowpass filter-
ing the output signal is suggested in applications where
only DC measurements are required. Determining the
required filtering components is straightforward, as the
MAX4004 exhibits a very high output impedance
(>5MΩ), while the MAX4006 exhibits an output resis-
tance of 10kΩ.
In some applications where pilot tones are used to iden-
tify specific fiber channels, higher bandwidths are
desired at OUT to detect these tones. Consider the mini-
mum and maximum currents to be detected, then con-
sult the frequency response and noise typical operating
curves. If the minimum current is too small, insufficient
monitor bandwidth could result, while too high of a cur-
rent could result in excessive monitor noise across the
desired bandwidth.
High-Accuracy, High-Side Current Monitors
in SOT23
8
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In applications where power-supply noise can interfere
with DC diode measurements, additional filtering is sug-
gested. Such noise is commonly seen when switching
power supplies are used to generate the photodiode
bias voltage. As shown in the typical operating circuit, a
pi filter (two 0.22µF capacitors and one 2.2µH inductor)
greatly suppress power-supply switching noise. If such
a filter is already present in the bias-generating circuit,
only a simple bypass capacitor at the BIAS pin is sug-
gested. The output lowpass filter, a 10kΩ resistor and a
10nF capacitor, further reduce permeating power-sup-
ply noise as well as other wideband noise that might
otherwise restrict measurements at low signal levels.
Again, reducing the bandwidth of the OUT signal can
affect performance of pilot-tone systems.
To restrict high-frequency photodiode signals from
affecting the current monitor and BIAS power supply, an
RF choke and 10nF capacitor can be added. The
capacitance presented to REF should not exceed 10nF;
larger values increase startup time and could cause the
thermal shutdown circuit to activate during startup.
Bypassing and External Components