ADN2525ACPZ-R2 Analog Devices Inc, ADN2525ACPZ-R2 Datasheet - Page 14

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

ADN2525ACPZ-R2

Manufacturer Part Number
ADN2525ACPZ-R2
Description
IC,Laser Diode/LED Driver,LLCC,16PIN,PLASTIC
Manufacturer
Analog Devices Inc
Type
Laser Diode Driver (Fiber Optic)r
Datasheet

Specifications of ADN2525ACPZ-R2

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
Other names
ADN2525ACPZ-R2
ADN2525ACPZ-R2TR
ADN2525
DESIGN EXAMPLE
This design example covers:
• Headroom calculations for IBIAS, IMODP, and IMODN pins.
• Calculation of the typical voltage required at the BSET and
This design example assumes that the resistance of the TOSA is
25 Ω, the forward voltage of the laser at low current is V
IBIAS = 40 mA, IMOD = 60 mA, and VCC = 3.3 V.
Headroom Calculations
To ensure proper device operation, the voltages on the IBIAS,
IMODP, and IMODN pins must meet the compliance voltage
specifications in Table 1.
Considering the typical application circuit shown in Figure 33,
the voltage at the IBIAS pin can be written as
where:
VCC is the supply voltage.
V
R
V
V
For proper operation, the minimum voltage at the IBIAS pin
should be greater than 0.6 V, as specified by the minimum
IBIAS compliance specification in Table 1.
Assuming that the voltage drop across the 25 Ω transmission
lines is negligible and that V
40 mA,
The maximum voltage at the IBIAS pin must be less than the
maximum IBIAS compliance specification as described by
For this example:
To calculate the headroom at the modulation current pins
(IMODP and IMODN), the voltage has a dc component equal
to VCC due to the ac-coupled configuration and a swing equal
to IMOD × 25 Ω. For proper operation of the ADN2525, the
voltage at each modulation output pin should be within the
normal operation region shown in Figure 30.
TOSA
F
LA
LB
MSET pins to produce the desired bias and modulation currents.
is the forward voltage across the laser at low current.
is the dc voltage drop across L1, L2, L3, and L4.
is the dc voltage drop across L5, L6, L7, and L8.
V
V
V
V
V
V
is the resistance of the TOSA.
IBIAS
IBIAS
IBIAS
COMPLIANCE_MAX
COMPLIANCE_MAX
IBIAS
= VCC − V
= 3.3 − 1 − (0.04 × 25) = 1.3 V
= 1.3 V > 0.6 V, which satisfies the requirement
= 1.3 V < 2.53 V, which satisfies the requirement
= VCC − 0.75 − 4.4 × IBIAS (A)
= VCC – 0.75 − 4.4 × 0.04 = 2.53 V
F
− (IBIAS × R
LA
= 0 V, V
TOSA
F
) − V
= 1 V, and IBIAS =
LA
F
= 1 V,
Rev. A | Page 14 of 16
Assuming V
at the modulation output pins is equal to
The maximum voltage at the modulation output pins is equal to
Headroom calculations must be repeated for the minimum and
maximum values of the required IBIAS and IMOD ranges to
ensure proper device operation over all operating conditions.
BSET and MSET Pin Voltage Calculation
To set the desired bias and modulation currents, the BSET and
MSET pins of the ADN2525 must be driven with the appropriate
dc voltage. The voltage range required at the BSET pin to generate
the required IBIAS range can be calculated using the BSET
voltage to IBIAS gain specified in Table 1. Assuming that
IBIAS = 40 mA and the typical IBIAS/V
the BSET voltage is given by
The BSET voltage range can be calculated using the required
IBIAS range and the minimum and maximum BSET voltage to
IBIAS gain values specified in Table 1.
The voltage required at the MSET pin to produce the desired
modulation current can be calculated using
where K is the MSET voltage to IMOD ratio.
The value of K depends on the actual resistance of the TOSA.
It can be read using the plot shown in Figure 29. For a TOSA
resistance of 25 Ω, the typical value of K = 120 mA/V. Assuming
that IMOD = 60 mA and using the preceding equation, the
MSET voltage is given by
The MSET voltage range can be calculated using the required
IMOD range and the minimum and maximum K values. These
can be obtained from the minimum and maximum curves in
Figure 29.
VCC − (IMOD × 25)/2 = VCC − 0.75
VCC − 0.75 > VCC − 1.1 V, which satisfies the requirement
VCC + (IMOD × 25)/2 = VCC + 0.75
VCC + 0.75 < VCC + 1.1 V, which satisfies the requirement
V
V
V
MSET
BSET
MSET
=
=
=
LB
IBIAS
100
IMOD
IMOD
= 0 V and IMOD = 60 mA, the minimum voltage
120
K
mA/V
mA/V
(mA)
(mA)
=
=
100
40
120
60
=
=
0
4 .
0
5 .
V
V
BSET
ratio of 100 mA/V,

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