CS6707 Myson Technology, CS6707 Datasheet - Page 4

• Manufacturer Part Number: CS6707
• Description: 200Mbps Fiber Optic Led Driver
• Manufacturer: Myson Technology

PRODUCT DESCRIPTION
The CS6707 consists of a modulation current drive with temperature compensation, the pulse width adjustment
circuit, the peaking and clamping circuit.
Modulation Current Drive With Temperature Compensation
A. Temperature Independent
The modulation current (Imod) can be set by connecting a resistor Rset bwtween the Rmod pin and the ground.
One can set Imod by choicing the unique Rset from the figure -4 or figure-5 depending on Vdd=3.3V or Vdd=5V.
The figure-4 and figure-5 show the relation between Imod and Rset independent of temperature compensation.
The approximation relation between Imod and Rset is
Vref is the voltage at the Rmod pin about 1.13V, K1 is 1100 100.
B. Temperature Dependent
If the temperature compensation of the LED current is desired. One can use the Table-1, Figure-6, Figure-4,
Figure-5 to implement the temperature compensation feature. The Table-1 and Figure-6 show the internal diode
threshold voltage (Vth) via the various R
Rmod pin and the Rmod1 pin. One can use the formula below to set the R
T2 and T1 are the different termperature, T2 >T1. Then use
to set the Rset value.
The pulse width adjustment
The pulse width of the LED ON/OFF time can be set with connecting the PWAI and PWAD pins to the ground by
a resistor Rpwai and Rpwad individually. If let Rpwad floating and Rpwai connect, the LED ON time will increase.
If let Rpwai floating and Rpwad connect, the LED ON time will decrease. Refer to the Fingure-7, Fingure-8,
Fingure-9 and Fingure-10 to get the Rpwai and Rpwad setting.
The peaking and clamping circuit
Generally. The turn-off time of the LED is longer than the turn-on time. One can use the clamping circuit to
improve this situation. The clamping feature can get by the V
the clamping feature is off. The clamping circuit will delay the turn-on time of the LED. It becomes noticeable
when the LED driving current is low. One can connect a RC network between the MODP and PEAK pins to slove
this problem. See the application ciucuits to get the detail information.
Imod (T1) = K1 x [
R
TCM
TCM
.
= K1 x
.
value at different temperature, which R
Imod = K1 x
Vth (T1)
Imod (T2)
Rset
Vref
+
Rset
Vref
Vref - Vth (T1)
DD3
Vth (T2)
Imod (T1)
R
pin connection. If the V
TCM
TCM
]
.
TCM
is a resistor between the
DD3
pin is floating, then
CS6707
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