DS1842A Maxim, DS1842A Datasheet - Page 6

• Manufacturer Part Number: DS1842A
• Description: The DS1842A integrates the discrete high-voltage components necessary for avalanche photodiode (APD) bias and monitor applications
• Manufacturer: Maxim

76V, APD, Dual Output Current Monitor
Figure 1. Current Clamp from Current Feedback
The mirror output is typically connected to an ADC
using a resistor to convert the mirrored current into a
voltage. The resistor to ground should be selected such
that the maximum full-scale voltage of the ADC is
reached when the maximum mirrored current is
reached. For example, if the maximum monitored cur-
rent through the APD is 2mA with a 1V ADC full scale,
and the 10:1 mirror is used, then the correct resistor is
approximately 5kΩ. If both MIR1 and MIR2 are con-
nected together, the correct resistor is 1.6kΩ.
The mirror response time is dominated by the amount of
capacitance placed on the output. For burst-mode Rx
systems where the fastest response times are required
(approximately a 50ns time constant), a 3.3pF capacitor
and external op amp should be used to buffer the signal
sent to the ADC. For continuous mode applications, a
10nF capacitor is all that is required on the output.
The DS1842A has a current clamping circuit to protect
the APD by limiting the amount of current from MIROUT.
There are three methods of current clamping available:
1) Internally Defined Current Limit
The device’s current clamp circuit automatically
clamps the current when it exceeds the maximum
MIROUT current.
2) External Shutdown Signal
The CLAMP pin can completely shut down the current
from MIROUT. The CLAMP pin is active high.
3) Precise Level Set by External Feedback Circuit
A feedback circuit is used to control the level applied to
the CLAMP pin. Figure 1 shows an example feedback
circuit.
6
_______________________________________________________________________________________
MIR1
REF
Current Clamp
CLAMP
As a safety feature, the DS1842A has a thermal-shut-
down circuit that turns off the MIROUT and MIRIN cur-
rents when the internal die temperature exceeds
T
cooled.
The DS1842A includes a resistor-divider to use as the
feedback network for the boost converter. The
DS1842A resistor-divider ratio, K
controlled, allowing the boost converter output to be set
with very high precision. K
internal DC-DC boost controller. K
modified by adding external series/parallel resistors;
however, the temperature coefficient of the external
resistors must be considered.
For the latest package outline information and land patterns
(footprints), go to www.maxim-ic.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.
SHDN
14 TDFN-EP
PACKAGE
TYPE
. These currents resume after the device has
PACKAGE
T1433+2
CODE
Package Information
Precision Voltage-Divider
R
can pair with the DS1875’s
OUTLINE
Thermal Shutdown
21-0137
NO.
R
R
can also be easily
(R
1
/R
PATTERN NO.
2
), is tightly
90-0063
LAND