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參數(shù)資料
| 型號(hào)： | M61880FP |
| 廠商： | Mitsubishi Electric Corporation |
| 英文描述： | Laser-diode driver / controller |
| 中文描述： | 激光二極管驅(qū)動(dòng)器/控制器 |
| 文件頁數(shù)： | 3/11頁 |
| 文件大?。?/td> | 160K |
| 代理商： | M61880FP |
( / )
3
MITSUBISHI
<
DIGITAL ASSP
>
M61880FP
Laser-diode driver / controller
OPERATION
1.Laser Drive Currents Setting Method
Laser Drive Current=Isw(switching current)+I
B
(bias current)
at switching mode
(1)Isw(Switching Current)
First it is necessary to decide the center value(Isw0) of
maximum switching current Isw(max).Isw0 is depend on
Rs ( load for switching current setting) by the following
equation.
(a)
Rs [k
]
(b) When switching current is center value( Isw0) , it is
necessary to set up Rm ( load resistor for monitor of
photodiode current ) as follows:
V
M
(voltage across resistor Rm) = Vr (reference voltage )
at this condition C
H
pin voltage =2.5V.
When C
H
pin voltage < 2.5V , Isw <Isw0
When C
H
pin voltage > 2.5V , Isw >Isw0
(C
H
pin voltage changes from 2V to 3V at APC mode)
(c) The usable range of ISW at APC mode
That is 20 ~180% of Isw0 accurately.
(2) I
B
(Bias Current)
Bias current (I
B
) is set by R
B
(resistor for the setting of
bias current) and V
B
(voltage for the setting of bias current).
Vref(1.5V) [V]
Isw0 [mA] = 30 X
Vcc < 3.5V(typ.), and the C
H
pin is compulsorily fixed to "L"
at the same time.
5.RO Pin
A load resistor for laser drive current is connected to the RO
pin, through which a current almost equal to Isw flows in.
The load resistor is connected between the RO pin and Vcc
to reduce power dissipated in the IC.
Due to reasons related to the operation of circuits, the voltage
at this pin should be 2.5V or higher.
Consequently, the maximum resistance, RO(max.), of load re-
sistor RO is :
Vcc(min.) -2.5 [V]
Isw(max.) [mA]
where Isw(max.) is the maximum of Isw. If, for example,
Vcc(min.)= 4.75V and Isw(max.)= 100mA, RO(max.)=22
.
Accordingly, if the resistance of RS is selected so as to gain
maximum Isw of 100mA, RO should be 22
at the maxi-
mum.
6.Sample-Hold Circuit
(1) Circuit Operation Overview
The following is an overview of the operation of the sample-
hold circuit contained in the M61880.
The PD current generated by LD illumination flows through
the resistor connected between 1RM and 2RM, thereby gen-
erating a potential difference(Vm). Vm is compared with the
voltage applied to the Vr pin. If Vm < Vr , a constant current is
sourced through the C
H
pin so that the external capacitor is
charged. If Vm > Vr , a constant current sinks through the C
H
pin to discharge the external capacitor. This operation occurs
when the S/H input is "L" and DATA= "L" (sample).
When the S/H input is "H" , the C
H
pin is maintained at high
impedance state(hold), irrespective of the state of Vm, Vr, and
DATA input.
RO(max.) [
] =
4.Internal Reset Function
The M61880 has a reset circuit built in for the protection of
laser from an excessive current flowing at the moment of
power on. The internal current source goes off in the range
I
B
[A] = 1 X
V
B
[V]
R
B
[
]
2.Switching Operation
If DATA = "L" , the LD drive current is Isw+I
B
if DATA = "H" , I
B
.
3.ENB input
When the laser drive current is controlled by the DATA input,
the M61880's internal current source is maintained turned on.
In contrast, the control by ENB is turning on and off at the cur-
rent source. If ENB = "L" the current source turns on ; if ENB
= "H" off.
When ENB = "H" the C
H
pin is compulsorily fixed to "L" in
order to discharge the capacitor connected to the C
H
pin.
1.2V
≤
V
B
≤
Vcc-2.7V
I
B
(max.)=40mA
11
Conceptual Diagram: sample-hold circuit
External
capacitor
S / H
ENB
Constant
current source
for discharging
SW1
SW2
CH
Control
circuit
Tr1
Comparator
Vr
Vm
Constant
current source
for charging
Output
1.0
2.0
3.0
4.0
2.5
Isw0
0%
100%
200%
2Isw0
0
CH pin voltage
VCH (V)
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