SM8610CV datasheet(7/9 Pages) NPC

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SM8610CV

NIPPON PRECISION CIRCUITS INC.—7

Laser Diode Drive Current Mid-value Set Function

The laser diode drive current mid-value can be adjusted by changing the resistance RLD connected between the

LDISET and GND pins. The laser diode drive current mid-value base value ILDSET, given by the following

equation, is set to the LDIOUT output current when the PDVIN voltage is in balance state (147 to 193mV).

Note that the actual LDIOUT current may change due to feedback gain, and laser diode/photo diode variations.

APC Loop Gain Setting

The APC (Auto Power Control) loop gain can be adjusted by changing the external gain set resistance (RG)

connected between the RG1 and RG2 pins. The PDVIN voltage-to-laser drive current open-loop gain is given

approximately by the following equation.

APC Loop Cutoff Frequency Setting

The APC loop cutoff frequency fc is determined by the external resistance RG and the capacitance CG, con-

nected between RG1 and RG2.

If CG is connected between RG2 and VCC, the cutoff frequency is given as follows.

RLD : LDISET connected resistance [Ω]

∆LDIOUT current /∆PDVIN voltage ratio [S]

RG : Resistance connected between RG1 and RG2 [Ω]

ILDSET = ILDSET

× 1000 =

RLD

800[V]

[A]

GmPDVIN = 9.1

× 10 −5 RG [S]

fC1 =

πRGCG

[Hz]

fC2 =

πRGCG

[Hz]

√

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