General Description
The DS1842A integrates the discrete high-voltage
components necessary for avalanche photodiode
(APD) bias and monitor applications. A precision volt-
age-divider network is used in conjunction with an
external DC-DC controller and FET to create a boost
DC-DC converter. A current clamp limits current
through the APD and also features an external shut-
down. The precision voltage-divider network is provid-
ed for precise control of the APD bias voltage. The
device also includes a dual current mirror to monitor
the APD current.
Applications
APD Biasing
GPON ONU and OLT
Features
♦76V Maximum Boost Voltage
♦Current Monitor with a Wide 1µA to 2mA Range,
Fast 50ns Time Constant, and 10:1 and 5:1 Ratio
♦2mA Current Clamp with External Shutdown
♦Precision Voltage Feedback
♦Multiple External Filtering Options
♦3mm x 3mm, 14-Pin TDFN Package with Exposed Pad
DS1842A
76V, APD, Dual Output Current Monitor
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
19-4994; Rev 1; 9/11
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE PIN-PACKAGE
DS1842AN+ -40°C to +85°C 14 TDFN-EP*
DS1842AN+T&R -40°C to +85°C 14 TDFN-EP*
+
Denotes a lead(Pb)-free/RoHS-compliant package.
T&R = Tape and reel.
*
EP = Exposed pad.
DS4830
DS1842A
PWM
ADC
GPIO
ADC
FBOUT
R1
R2
MIRIN
FBIN
MIR1
CLAMP
MIROUTGNDEP
3.3V
CURRENT MIRROR
CURRENT
LIMIT MIR2
CBULK
EXTERNAL MONITOR
TIA
APD
ROSA
Typical Application Circuit
DS1842A
76V, APD, Dual Output Current Monitor
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(TA= -40°C to +85°C, unless otherwise noted.)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Note 2: Rising MIROUT transition from 10µA to 1mA; VMIRIN = 40V, 2.5kΩload.
Note 3: Not production tested. Guaranteed by design.
Voltage Range on CLAMP
Relative to GND...................................................-0.3V to +12V
Voltage Range on MIRIN, MIROUT, FBIN
MIR1, and MIR2 Relative to GND........................-0.3V to +80V
Voltage Range on FBOUT Relative to GND ..........-0.3V to +6.0V
Continuous Power Dissipation (TA = +70°C)
TDFN (derate 24.4mW/°C above +70°C).................1951.2mW
Operating Junction Temperature Range...........-40°C to +150°C
Storage Temperature Range .............................-55°C to +135°C
Lead Temperature (soldering, 10s) .................................+300°C
Soldering Temperature (reflow) .......................................+260°C
PACKAGE THERMAL CHARACTERISTICS (Note 1)
TDFN
Junction-to-Ambient Thermal Resistance (θJA) ............41°C/W
Junction-to-Case Thermal Resistance (θJC) ...................8°C/W
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
CLAMP Voltage VCLAMP 0 11 V
CLAMP Threshold VCLT 1.25 1.8 2.35 V
CLAMP = low 1.8 2.75 3.85 mA
Maximum MIROUT Current IMIROUT CLAMP = high 10 μA
MIR1 to MIROUT Ratio KMIR1 15V < VMIRIN < 76V, IMIROUT > 1μA 0.096 0.100 0.104 A/A
MIR2 to MIROUT Ratio KMIR2 15V < VMIRIN < 76V, IMIROUT > 1μA 0.192 0.200 0.208 A/A
MIR1, MIR2 Rise Time
(20%/80%) tRC (Note 2) 30 ns
Shutdown Temperature TSHDN (Note 3) +150 °C
Hysteresis Temperature THYS (Note 3) 5 °C
Leakage on CLAMP IIL -1 +1 μA
Resistor-Divider Ratio (R1/R2) KR T
A = +25°C, VFBIN = 76V 59.5 60.25
Resistor-Divider Tempco ±50 ppm/°C
Resistor-Divider End-to-End
Resistance RRES T
A = +25°C, VFBIN = 76V 308 385 481 k
Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer
board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial.
DS1842A
76V, APD, Dual Output Current Monitor
_______________________________________________________________________________________
3
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MIRIN CURRENT vs. MIROUT CURRENT
(VMIRIN = 40V)
DS1842A toc01
MIROUT CURRENT (
µ
A)
MIRIN CURRENT (µA)
100010010
100
1000
10,000
10
1 10,000
MIRIN CURRENT vs. TEMPERATURE
(VMIRIN = 40V, IMIROUT = 250nA)
DS1842A toc02
TEMPERATURE (°C)
MIRIN CURRENT (µA)
806020 400-20
10
20
30
40
50
60
70
80
90
100
0
-40 100
MIRIN CURRENT vs. TEMPERATURE
(VMIRIN = 40V, IMIROUT = 2mA)
DS1842A toc03
TEMPERATURE (°C)
MIRIN CURRENT (mA)
806040200-20
1
2
3
4
5
0
-40 100
MIR ERROR vs. TEMPERATURE
(IMIROUT = 1
µ
A)
DS1842A toc04
TEMPERATURE (°C)
ERROR (%)
806040200-20
-1
0
1
2
-2
-40 100
VMIRIN = 40V
MIR2
MIR1
MIR ERROR vs. TEMPERATURE
(IMIROUT = 1mA)
DS1842A toc05
TEMPERATURE (°C)
ERROR (%)
806040200-20
-1
0
1
2
-2
-40 100
VMIRIN = 40V
MIR2
MIR1
MIR ERROR vs. MIROUT CURRENT
DS1842A toc06
MIROUT CURRENT (
µ
A)
ERROR (%)
100010010
-1
0
1
2
-2
1 10,000
VMIRIN = 40V
MIR2
MIR1
DS1842A
76V, APD, Dual Output Current Monitor
4 _______________________________________________________________________________________
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
MIR ERROR
vs. MIRIN VOLTAGE
DS1842A toc07
MIRIN VOLTAGE (V)
ERROR (%)
706050403020
-1
0
1
2
-2
10 80
IMIR2 = 1µA
IMIR1 = 1µA
IMIR2 = 1mA
IMIR1 = 1mA
MIROUT CLAMP CURRENT
vs. MIRIN VOLTAGE
DS1842A toc08
MIRIN VOLTAGE (V)
IMIROUT (mA)
706040 503020
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
3.5
2.5
10 80
TA = -40°C
TA = +25°C
TA = +85°C
RESISTOR-DIVIDER RATIO
vs. FBIN VOLTAGE
DS1842A toc11
FBIN VOLTAGE (V)
RATIO (KR)
706050403020
59.8
59.9
60.0
60.1
59.7
10 80
RESISTOR-DIVIDER RATIO
vs. TEMPERATURE
DS1842A toc12
TEMPERATURE (°C)
RATIO (KR)
806040200-20
59.85
59.90
59.95
60.00
59.80
-40 100
VFBIN = 40V
DS1842A
76V, APD, Dual Output Current Monitor
_______________________________________________________________________________________ 5
Pin Description
PIN NAME FUNCTION
1 MIR1 Current Mirror Monitor Output, 10:1 Ratio
2 MIR2 Current Mirror Monitor Output, 5:1 Ratio
3, 6, 7 GND Ground Connection for Device. Connect directly to ground plane.
4 FBOUT Feedback Output. Resistor-divider output.
5 CLAMP Clamp Input. Disables the current mirror output (MIROUT).
8–11 N.C. No Connection
12 FBIN Feedback Input. Resistor-divider input.
13 MIRIN Current Mirror Input
14 MIROUT Current Mirror Output. Connect to APD bias pin.
— EP Exposed Pad. Connect directly to the same ground plane as GND.
Block Diagram
TDFN
TOP VIEW
2
4
5
13
11
10
MIRIN
N.C.
N.C.
MIR2
FBOUT
CLAMP
114 MIROUTMIR1
312 FBINGND
69N.C.GND
78N.C.GND
DS1842A
*EP
*EXPOSED PAD.
+
DS1842A
MIRIN
MIR1
CLAMP
MIROUT
CURRENT MIRROR
CURRENT
LIMIT
FBIN
MIR2
THERMAL
SHUTDOWN
FBOUT
R1
R2
GNDEP
Pin Configuration
Detailed Description
The DS1842A contains discrete high-voltage compo-
nents required to create an APD bias voltage and to
monitor the APD bias current. The device’s mirror out-
puts are a current that is a precise ratio of the output
current 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 APDs. The
APD current can also be shut down by CLAMP or ther-
mal shutdown. The resistor-divider is used in conjunc-
tion with a DC-DC boost controller and FET to precisely
create the APD bias voltage.
Current Mirror
The DS1842A has two current mirror outputs. One is a
10:1 mirror connected at MIR1, and the other is a 5:1
mirror connected to MIR2.
DS1842A
76V, APD, Dual Output Current Monitor
6 _______________________________________________________________________________________
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.
Current Clamp
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.
Thermal Shutdown
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
TSHDN. These currents resume after the device has
cooled.
Precision Voltage-Divider
The DS1842A includes a resistor-divider to use as the
feedback network for the boost converter. The
DS1842A resistor-divider ratio, KR(R1/R2), is tightly
controlled, allowing the boost converter output to be set
with very high precision. KRcan pair with the DS1875’s
internal DC-DC boost controller. KRcan also be easily
modified by adding external series/parallel resistors;
however, the temperature coefficient of the external
resistors must be considered.
Package Information
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.
CLAMP
MIR1
REF
Figure 1. Current Clamp from Current Feedback
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
14 TDFN-EP T1433+2 21-0137 90-0063
DS1842A
76V, APD, Dual Output Current Monitor
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 _____________________
7
© 2011 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 10/09 Initial release —
1 9/11
Removed references to the internal switch FET and renamed pins accordingly;
updated the soldering information in the Absolute Maximum Ratings section; added
the Package Thermal Characteristics section; removed the FET Typical Operating
Characteristics graphs
1, 2, 4, 5, 6
