M66512FP 데이터 시트보기 (PDF) - MITSUBISHI ELECTRIC

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M66512FP

LASER-DIODE DRIVER

MITSUBISHI ELECTRIC  

MITSUBISHI 〈DIGITAL ASSP〉

M66512P/FP

LASER-DIODE DRIVER

5. RO Pin

The RO pin is used to connect a load resistor (RO) for the

current sources (IL1, IL2, and IL3). The load resistor is con-

nected between the RO pin and VCC in order to reduce the

power dissipated in the IC.

The resistance of the load resistor should be such that does

not generate a voltage equal to or lower than 2.5V at the RO

pin. Accordingly, a value that satisfies the following equation

should be chosen.

RO (Ω)

≤

maximum

load

VCC–2.5[V]

current flowing

through

RO

[A]

Example: If VCC =5V and the maximum load current is 120

mA, RO is 20Ω or under.

6. Internal Reset Function

The M66512 has a reset circuit for the protection of laser from

an excessive current flowing at the moment of power on. The

reset circuit functions in the range VCC < 3.5V(typ.), letting all

current sources turn off.

7. VCC and GND Pins

Pins related to the power supply function are VCC1, VCC2,

GND1, and GND2. The role of these pins in terms of the in-

ternal circuits are as follows.

VCC1, GND1 : connected to analog circuits

VCC2, GND2 : connected to digital circuits

In practical wiring, the following should be noted.

(1) Secure as much a width as possible for conductors and

avoid lengthy wiring.

(2) Allocate electrolytic capacitors for stable voltage near

VCC1 and GND1.

(3) Allocate by-pass capacitors near VCC2 and GND2.

Notes on the Wiring for peripheral Components

Lay out peripheral components necessary for the M66512 to

operate in closest possible proximity to the M66512.

Calculation Method for Power Dissipation

The M66512’s approximated power dissipation, P, is deter-

mined by the following equation.

P=ICC × VCC +I(RO) × V(RO) + I(LD) × V(LD) + IOL(CO) × VOL(CO)

Where V(RO) : voltage at RO pin

V(LD) : voltage at LD pin

I(RO) : load current at RO pin

I(LD) : load current at LD pin

VOL(CO) : “L” output voltage at CO pin

IOL(CO) : “L” output voltage at CO pin

If, for example, VCC = 5.25V, V(RO) = V(LD) = 2.75V, I(RO) =

I(LD) = 120mA, IOL(CO) = 8mA, and VOL(CO) = 0.5V, power dis-

sipation at times of turning on and off of laser will be as fol-

lows.

(1) Laser ON (DATA =“L” and ICC = 75mA)

PON = 75 × 5.25 + 0 + 120 × 2.75 + 8 × 0.5 = 727.8(mW)

(2) Laser OFF (DATA =“H” and ICC = 74mA)

POFF = 74 × 5.25 + 120 × 2.75 + 0 = 718.5(mW)

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