M61880FP Datasheet, PDF (5/21 Pages) Mitsubishi Electric Semiconductor – Laser-diode driver / controller

M61880FP
Comparator
Reference voltage input
RM resistance generation voltage
Control circuit
Sample-and-hold control input S/H
ENB
Charging constant-
current source
SW1
Output (CH pin)
SW2
Discharging constant-
current source
CH ^{External capacitance}
Tr1
Conceptual Diagram of Sample-and-Hold Circuit
Operation Function Table
Input
ENB
S/H
H
X
L
H
L
L
X: Don’t Care
DATA
X
X
H
L
VM, Vr
X
X
X
VM < Vr
VM > Vr
Switch State
SW1
SW2
OFF
OFF
OFF
OFF
OFF
OFF
ON
OFF
OFF
ON
Tr1
ON
OFF
OFF
OFF
OFF
Output (CH Pin)
Fixed at “L”
High-impedance state (hold)
High-impedance state (hold)
Current source (sample)
Current sink (sample)
(2) APC timing chart
An example of a timing chart of APC operation by means of the sample-and-hold control signals is shown below.
In this example, a case is shown in which the direction of the CH pin leakage current in the hold state is assumed to be
the direction of flow to the M61880 (forward direction).
Power supply
ENB input
S/H input
Sample
Hold
Sample
Hold
Sample _Hold
DATA input
Laser drive
current
∆ILD
Example of Sample-and-Hold Type APC Circuit Operation Timing Chart
Rev.1.0, Sep.19.2003, page 5 of 20