REV. 0

–4–

AD9660

PIN DESCRIPTIONS

Pin

Function

OUTPUT

Analog laser diode current output. Connect to anode of laser diode, cathode connected to GROUND externally.

BIAS LEVEL

tion as follows:

I

V

1.85

× R

()

BIAS CAL

TTL/CMOS compatible, Bias loop T/H control signal. Logic HIGH enables calibration mode, and the bias loop

T/H immediately goes into track mode. Logic LOW disables the bias loop T/H and immediately places it in hold

mode. WRITE PULSE should be held logic LOW while calibrating. Floats logic HIGH.

BIAS HOLD

External hold capacitor for the bias loop T/H. Approximate droop in the bias current while BIAS CAL is logic

18

×10

–9

t

BIAS HOLD

C

BIAS HOLD

1

2

π (550 Ω)C

BIAS HOLD

WRITE PULSE

WRITE CAL

TTL/CMOS compatible, write loop T/H control signal. Logic HIGH enables calibration mode; before enabling

calibration the bias loop should be calibrated and OFFSET PULSE driven to an appropriate state. In calibration

mode, 13 ns after the WRITE PULSE goes logic HIGH, the write loop T/H goes into track mode (there is no de-

lay if WRITE PULSE is HIGH before WRITE CAL transitions to a HIGH level). The write loop T/H immedi-

ately goes into hold mode when the WRITE PULSE goes Logic LOW. WRITE CAL LOW disables the write

loop T/H and places it in hold mode. Floats logic HIGH.

WRITE LEVEL

V

1.85

× (R

WRITE HOLD

18

×10

−9

t

WRITE HOLD

C

WRITE HOLD

. Bandwidth of the loop is:

BW

=

1

2

π (550 Ω) C

BIAS HOLD

SENSE IN

of the PIN diode, with the PIN anode connected to GROUND or a negative voltage. Voltage at SENSE IN var-

ies slightly with temperature and current, but is typically 4.0 V.

GAIN

POWER

Output voltage monitor of the internal feedback loop. Voltage is proportional to feedback current from photo

MONITOR

diode.

OFFSET

CURRENT SET determines offset current level. The input voltage at this node varies slightly with temperature and current, but is

typically 1.4 V. See curves. Can also be driven with a current out DAC.

OFFSET

PULSE

DISABLE

TTL/CMOS compatible, current output disable circuit. Logic LOW for normal operation; logic HIGH disables

output current when the device is re-enabled). DISABLE floats logic HIGH.

Analog Voltage Output, internal bandgap voltage reference, ~1.75 V, provided to user for power level offset.

Positive Power Supply. Nominally +5 V, pin connections should be tied together externally.

GROUND

Ground Reference. All grounds should be tied together externally.