ADN2525ACPZ-REEL7 Analog Devices Inc, ADN2525ACPZ-REEL7 Datasheet - Page 9

IC,Laser Diode/LED Driver,LLCC,16PIN,PLASTIC

ADN2525ACPZ-REEL7

Manufacturer Part Number
ADN2525ACPZ-REEL7
Description
IC,Laser Diode/LED Driver,LLCC,16PIN,PLASTIC
Manufacturer
Analog Devices Inc
Type
Laser Diode Driver (Fiber Optic)r
Datasheet

Specifications of ADN2525ACPZ-REEL7

Data Rate
10.7Gbps
Number Of Channels
1
Voltage - Supply
3.07 V ~ 3.53 V
Current - Supply
39mA
Current - Modulation
80mA
Current - Bias
100mA
Operating Temperature
-40°C ~ 85°C
Package / Case
16-VFQFN, CSP Exposed Pad
Mounting Type
Surface Mount
Lead Free Status / RoHS Status
Lead free / RoHS Compliant

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THEORY OF OPERATION
As shown in Figure 1, the ADN2525 consists of an input stage
and two voltage-controlled current sources for bias and
modulation. The bias current is available at the IBIAS pin. It is
controlled by the voltage at the BSET pin and can be monitored
at the IBMON pin. The differential modulation current is
available at the IMODP and IMODN pins. It is controlled by
the voltage at the MSET pin. The output stage implements the
active back-match circuitry for proper transmission line
matching and power consumption reduction. The ADN2525
can drive a load having differential resistance ranging from 5 Ω
to 50 Ω. The excellent back-termination in the ADN2525
absorbs signal reflections from the TOSA end of the output
transmission lines, enabling excellent optical eye quality to be
achieved even when the TOSA end of the output transmission
lines is significantly misterminated.
INPUT STAGE
The input stage of the ADN2525 converts the data signal applied
to the DATAP and DATAN pins to a level that ensures proper
operation of the high speed switch. The equivalent circuit of the
input stage is shown in Figure 17.
The DATAP and DATAN pins are terminated internally with a
100 Ω differential termination resistor. This minimizes signal
reflections at the input, which could otherwise lead to degradation
in the output eye diagram. It is not recommended to drive the
ADN2525 with single-ended data signal sources.
DATAN
DATAP
Figure 17. Equivalent Circuit of the Input Stage
VCC
VCC
50Ω
50Ω
VCC
Rev. A | Page 9 of 16
The ADN2525 input stage must be ac-coupled to the signal
source to eliminate the need for matching between the common-
mode voltages of the data signal source and the input stage of
the driver (see Figure 18). The ac-coupling capacitors should
have an impedance less than 50 Ω over the required frequency
range. Generally, this is achieved using 10 nF to 100 nF capacitors.
BIAS CURRENT
The bias current is generated internally using a voltage-to-current
converter consisting of an internal operational amplifier and a
transistor, as shown in Figure 19.
The voltage-to-current conversion factor is set at 100 mA/V by
the internal resistors, and the bias current is monitored using a
current mirror with a gain equal to 1/100. By connecting a 1 kΩ
resistor between IBMON and GND, the bias current can be
monitored as a voltage across the resistor. A low temperature
coefficient precision resistor must be used for the IBMON
resistor (R
tolerances, or drift in its value over temperature, contributes to
the overall error budget for the IBIAS monitor voltage. If the
IBMON voltage is being connected to an ADC for A/D
conversion, R
minimize errors due to voltage drops on the ground plane.
Figure 18. AC-Coupling the Data Source to the ADN2525 Data Inputs
Figure 19. Voltage-to-Current Converter Used to Generate IBIAS
DATA SIGNAL SOURCE
BSET
IBMON
50Ω
IBMON
). Any error in the value of R
ADN2525
800Ω
200Ω
should be placed close to the ADC to
50Ω
GND
R
200Ω
C
C
VCC
R
2Ω
DATAP
DATAN
I
I
BMON
BIAS
ADN2525
IBMON
IBMON
IBIAS
due to
ADN2525

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