Micro Linear Corporation ML4632CS, ML4632CP Datasheet
March 1997
ML4632
Fiber Optic LED Driver
GENERAL DESCRIPTION
The ML4632 is a fiber optic LED driver suited for network
applications up to 20Mbps. The part is capable of driving
up to 100mA of current through a Fiber Optic LED from
an ECL or TTL level input signal. Its efficient output stage
provides a high current that can be programmed for
accurate absolute output level as well as automatic
temperature compensation. The combination of automatic
temperature compensation and a highly accurate current
driven design insures precise launch power.
The LED driver’s output stage provides fast, well matched
rise and fall times through a unique class B output stage
that burns supply current only when the LED is on. A
positive temperature coefficient of up to 3300ppm/°C can
be programmed into the output current to compensate for
the negative temperature coefficient of the LED optical
output power. An optional peaking circuit may also be
employed.
The ECL and TTL inputs are ANDed so one can be used
for data and the other for an enable input. An ECL
compatible BIAS voltage is also provided for single ended
ECL applications.
FEATURES
■ Current Driven Output for accurate Launch Power
■ Programmable output current from 20mA to 100mA
■ Programmable temperature coefficient, 0 to 3300ppm/°C
■ High Efficiency Output Stage
■ Programmable LED pre-bias current
■ Low EMI/RFI Noise
■ ECL or TTL inputs
■ Optional Peaking circuit
APPLICATIONS
■ IEEE 802.3, 10BASE-F
■ IEEE 802.5 Fiber Optic Token Ring
■ IEEE 802.4 Fiber Optic Token Bus
■ Fiber Optic Data Communications and
Telecommunications
BLOCK DIAGRAM
ECLP
ECLN
VBIAS
TTL
V
CC
GND
PEAK
+
14
BUFFER
–
1
2
13
8
REF
4
9
I
OFF
PEAK
DRIVER
DRV
AMP
PTAT
7
6
RPK
LED
3
RTSET
5
11
DRV
VREF
10
PTAT
12
1
ML4632
PIN CONFIGURATION
ML4632
14-Pin PDIP (P14)
ECLN
VBIAS
LED
GND
RTSET
RPK
PEAK
1
2
3
4
5
6
7
TOP VIEW
ECLP
14
TTL
13
PTAT
12
DRV
11
VREF
10
I
9
OFF
V
8
CC
PIN DESCRIPTION
NAME FUNCTION
ECLN Negative ECL data input. Tie to VBIAS for
single ended ECL operation or when ECLP is
used as an enable. Tie to ground during TTL
only operation.
VBIAS BIAS voltage for single ended ECL operation.
LED Fiber optic LED drive pin. Connect the LED
between this pin and VCC.
GND Negative power supply. The pin should be
tied to the grounded side of RTSET to improve
output accuracy and avoid a ground loop.
RTSET Output current programming pin. Connect a
resistor of value V
DRV/ILED
ground to set the high LED output current.
RPK Peaking circuit bias pin. Connect a resistor of
value V
DRV/IPEAK
from this pin to ground
when using the peaking circuit. Leave open
circuited when peaking is not used.
PEAK Peaking circuit output pin. When using
peaking, connect this pin to VCC through a
resistor of value RRPK. Then connect a
capacitor from this pin to the LED cathode.
When peaking is not used, open circuit RPK.
from this pin to
ML4632
16-Pin Wide SOIC (S16W)
ECLN
VBIAS
LED
GND
RTSET
RPK
PEAK
NC
NAME FUNCTION
V
I
OFF
CC
Positive power supply. +5 volts.
Connect a resistor from this pin to VCC to
1
2
3
4
5
6
7
8
TOP VIEW
ECLP
16
TTL
15
PTAT
14
DRV
13
VREF
12
I
11
10
9
V
NC
OFF
CC
increase the off current to the LED, i.e. 4.3KΩ
for 1mA. With this pin open, the default I
OFF
current is between 0.5–1.0mA.
VREF A constant 1.2V reference output used to set
up DRV.
DRV A DC input that sets the positive swing on
RTSET and the high level output current to
the LED.
PTAT Proportional to Absolute Temperature. A 1.0V
reference at 25°C that moves proportional to
absolute temperature, also used to set up
DRV. (See figure 1)
TTL TTL data input. Can also be used as an enable
during ECL operation. TTL = High (enabled),
TTL = Low (disabled).
ECLP Positive ECL data input controls signal to the
LED. Tie to VBIAS during TTL only operation
or use as an enable.
2
ABSOLUTE MAXIMUM RATINGS
ML4632
Absolute maximum ratings are those values beyond which
the device could be permanently damaged. Absolute
maximum ratings are stress ratings only and functional
PEAK DC Output Current ..................................... 120mA
Storage Temperature .............................. –65°C to +150°C
Lead Temperature (Soldering 10 sec.) ..................... 260°C
device operation is not implied.
V
............................................................................... –0.3V to 6V
CC
Input Pin Voltages ............................. –0.3V to VCC +0.3V
LED Output Current ............................................. 120mA
ELECTRICAL CHARACTERISTICS
Over the recommended operating conditions of T
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
CC
VREF VREF Voltage No Load 1.14 1.20 1.26 V
V
PTAT
V
I
LEDH
I
LEDL
t
t
PLH
t
PHL
t
PWD
V
V
PKTR
V
PKTF
I
ECL
I
TTL
V
I
OFF
VBIAS ECL BIAS Voltage VCC = 5V, T
Note 1: Limits are guaranteed by 100% testing, sampling or correlation with worst-case test conditions.
Note 2: Low Duty cycle pulse testing is performed at T
OS
R
t
F
PK
DO
Supply Current LED off 25 35 mA
PTAT Voltage No Load, T
Driver Offset VDRV = 1.2V, RTSET = 20Ω 50 mV
LED Current Accuracy VDRV = VREF, RTSET = 20Ω
High I
OFF
Low 0.5 0.7 1.0 mA
Rise Time VDRV = VREF, RTSET = 20Ω 4.5 ns
Fall Time VDRV = VREF, RTSET = 20Ω 4.5 ns
Propagation Delay VDRV = VREF, RTSET = 20Ω
Low to High TTL and ECL 10.0 ns
High to Low 10.0 ns
Pulse Width Distortion VDRV = VREF, RTSET = 20Ω 1.0 2.0 ns
Peaking Voltage R
Peaking Rise Time R
Peaking Fall Time R
ECL Input Current 20 µA
TTL Input Current 100 µA
Dropout Voltage between
pin 5 and 3 1.5 V
Additional LED Off Current VCC = 5V, R
.
A
= 0°C to 70°C, VCC = 5V ±5%, unless otherwise specified. (Note 1)
A
= 25°C 0.9 1.0 1.1 V
A
T
= 85°C 1.08 1.2 1.32 V
A
= open 54 60 66 mA
= 20Ω, C
RPK
= 20Ω, C
RPK
= 20Ω, C
RPK
= 100pF, R
PK
= 100pF, R
PK
= 100pF, R
PK
= 4.3KΩ 0.8 1.0 1.2 mA
IOFF
= 25°C 3.8 V
A
= 20Ω 1.08 1.2 1.32 V
PEAK
= 20Ω 4.5 ns
PEAK
= 20Ω 4.5 ns
PEAK
3
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