M66515FP データシートの表示（PDF） - Renesas Electronics

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M66515FP

Laser Diode Driver/Controller

Renesas Electronics 

M66515FP

5. RO pin

The RO pin is connected to the laser driving current load resistance; current essentially equal to ISW flows from this pin.

The load resistance is connected between this pin and VCC; by this means the Power dissipation within the IC is

reduced.

However, the circuit operation requires that the voltage at this pin be 2.5 V or above. Hence if the maximum value of

ISW is ISW(max), then the maximum value RO(max) of the load resistance RO is as follows.

For example, if VCC(min)=4.75 V and ISW(max)=120 mA, then RO(max)=18.8 Ω. In other words, when setting the

resistance RS such that the maximum value of ISW is 120 mA, RO should be 18.8 Ω or lower.

6. Sample-and-hold circuit

(1) Summary of circuit operation

The following is a summary of operation of the sample hold circuit within the M66515.

A PD current arising upon LD light emission flows through the resistance connected between 1RM and 2RM, giving

rise to a potential difference (VM). This VM is compared with the voltage applied to the pin Vr, and if VM<Vr, pin CH is

a constant current source which charges the external capacitor. If VM>Vr, pin CH is a constant current sink which

discharges the external capacitor. This operation is performed when the S /H input is "L" (sample); when the S/H input

is "H", the CH pin is kept in the high-impedance state (hold), regardless of VM, Vr, and the DATA input state.

Function table

Input

ENB

S/H

H

X

L

H

L

L

X: arbitrary

Vm, Vr

X

X

VM < Vr

VM > Vr

Switched state

SW1

SW2

OFF

OFF

OFF

OFF

ON

OFF

OFF

ON

Tr1

ON

OFF

OFF

OFF

Output

Fixed at "L"

High-impedance state (hold)

Constant current source (sample)

Constant current sink (sample)

(2) APC operation timing chart

An example of an APC operation timing chart for a given sample hold control signal is shown below.

In this example, a case is shown in which it is assumed that the direction of the leakage current of the CH pin in the hold

state is the direction flowing out from the M66515 (the negative direction).

Rev.1.00, Sep.22.2003, page 4 of 11

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