Closed-loop operation requires the user to establish

three internal currents with external resistors placed

between ground and the BIASSET, MODSET, and APC-

SET pins. See the

Design Procedures section for guide-

lines on selecting these resistor values.

Open-Loop Operation

If desired, the MAX3667 is fully operational without the

use of the APC loop. In these types of applications, the

laser diode current is set solely by the external resistors

connected to the BIASSET and MODSET pins. See the

Design Procedures section for instructions on setting

up the MAX3667 for open-loop operation.

Disable Control

The MAX3667 provides a single-ended TTL-compatible

disable control pin. The IBIAS, IMOD, and APCSET cur-

rents are disabled when the voltage on this pin is set

high. However, the internal voltage reference and other

sections of the MAX3667 remain active to ensure pre-

dictable operation and faster enable response times.

The disable response time is approximately 25ns.

Temperature Considerations

The MAX3667 contains a voltage reference that is fully

temperature compensated. This reference is used

throughout the circuit, as well as for programming the

+3.3V, 622Mbps SDH/SONET Laser Driver

with Automatic Power Control

_______________________________________________________________________________________

7

MAX3667

MODSET

1.0V

1.0V

1.0V

IN+

DISABLE

IBIAS

MD

PULLUP

IMOD

COMP

APC

31

Ω

IN-

MODMON

BIASSET

BIASMON

APCSET

1.0V

OTA

REFERENCE

Figure 2. Block Diagram