Datasheet

DS3920
Fast Current Mirror
6Maxim Integrated
Detailed Description
The DS3920 provides a fast, precision current mirror for
photodiode-monitoring applications. The current mirror
is accurate across a large dynamic range. The mirror
response time is fast enough to comply with GPON Rx
burst-mode monitoring requirements. The device has a
built-in current limiting feature to protect photodiodes
from large signal inputs, and an included thermal shut-
down. A diode is provided to limit the voltage at the MIR
output.
Current Mirror
The mirror output is typically connected to an analog-
to-digital converter (ADC) using a resistor to convert the
mirrored current into a voltage. The resistor to ground
should be selected so that the ADC’s full-scale voltage is
reached when the maximum mirrored current is reached.
For example, given that the maximum monitored current
through the APD is 2mA, 1.25V ADC full scale, and a 5:1
mirror ratio, the correct resistor is approximately 3.2kI.
The mirror response time is dominated by the amount of
capacitance placed on the output.
Current Clamp
The device features a current clamping circuit to protect
the photodiode by limiting the amount of current from
MIROUT to no more than I
MIROUT
. See the Ordering
Information for available current clamp options.
Diode Protection
A diode is internally connected from the MIR to DIODE
pins. This enables an external voltage applied to DIODE
to limit the voltage on MIR. The voltage applied to DIODE
should be equal to the desired V
MIR
limit minus the diode
forward voltage drop, or V
MIR
- V
DF
.
Thermal Shutdown
As a safety feature, the device has a thermal shutdown
circuit that turns off the MIROUT and MIR currents when
the internal die temperature exceeds T
SHDN
. The thermal
shutdown mechanism has a built-in hysteresis of T
HYST
.
Thus, the MIROUT and MIR currents resume once the
device has cooled to T
SHDN
- T
HYST
.
Ordering Information
+Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the
drawing pertains to the package regardless of RoHS status.
PART TEMP RANGE TYP CURRENT LIMIT (mA) PIN-PACKAGE
DS3920T-001+
-40NC to +85NC
20 6 SOT23
DS3920T-001+T
-40NC to +85NC
20 6 SOT23
DS3920T-002+
-40NC to +85NC
4.4 6 SOT23
DS3920T-002+T
-40NC to +85NC
4.4 6 SOT23
PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO.
6 SOT23 U6SN+1
21-0058 90-0175