Small, high-density precision DACs improve performance in laser-drive applications


In laser-drive applications, a major design consideration facing engineers today is implementing higher channel counts in fixed form factors. In this post, I will explore the benefits of using flexible and precise current sources at high channel counts in systems such as optical laser-drive applications, and examine technical documents and devices from TI that enable these benefits.

High-channel-count, high-precision digital-to-analog converters (DACs) such as the DAC80508 enable high-density and accurate current-source solutions where small size and high performance is required. As described in the application note, “High-Density DACs Offer Superior Noise and Accuracy Performance in Laser-Drive Applications,” laser diodes generally require a precisely controlled current to regulate their output power.

It is advantageous for this current to be adjustable because output power of the laser diode can change over temperature. For this reason, you can employ a DAC to dynamically update the forward current. In addition, you will want a low-noise source to reduce the laser output’s noise intensity (a manifestation of instability in the output power).

Current-output DACs that drive hundreds of milliamps in the market today come with some disadvantages: higher noise, thermal dissipation issues, lack of flexibility, etc. These disadvantages can be overcome by using a high-performing, voltage-output DAC with a voltage-to-current converter that can create a high-side current source to drive the laser diode.

Engineers are more frequently designing with higher channel counts in fixed form factors in laser-drive applications, and individual component size is very important to maximize channel density within these systems. The DACx0508 family enables designers to create dense, high-channel-count laser-drive solutions with maximum performance. For example, the DAC80508ZYZFT provides eight 16-bit voltage DAC channels in a 2.4-mm-by-2.4-mm die-size ball grid array (DSBGA) package with a very precise internal reference, providing the smallest 16-bit, eight-channel high-performance DAC on the market today.

The recently released reference design for laser diode applications with precisely controlled current requirements (see Figures 1 and 2) demonstrates a high-side current-source design implementing a multichannel DAC, operational amplifiers and discrete components to highlight overall size and performance for a variety of laser-drive applications.

Figure 1: Component size comparison

Figure 1: Component size comparison

Figure 2: Block diagram from reference design for laser diode applications  with precisely controlled current requirements

Figure 2: Block diagram from reference design for laser diode applications
with precisely controlled current requirements

The reference design has an output range of 200 mA and enables minimal power supply (PVDD) voltage compliance to reduce power consumption and thus enable high efficiency. It also features a low current-noise output, given the low reference noise from the components used.

If you have a laser-drive application that requires small, accurate, low-noise, high-side current-source solutions, consider the DAC60508, DAC70508 and DAC80508 DACs and OPA2376 op amp.

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