Flexible Sequencing
TI’s TPS40100 controller simplifies design by seamlessly supporting three common sequencing schemes found in today’s high performing power systems, including sequential sequencing, ratiometric sequencing and simultaneous sequencing. Such flexibility allows designers to effectively address the various sequencing requirements of complex systems with multiple output voltages without having to specify different controllers for each application. This saves valuable time, design effort and cost, especially if power supply sequencing requirements change when a digital signal processor (DSP) or field programmable gate array (FPGA) is changed mid-way through the design process—saving a designer from potentially having to re-design the entire power system. Using the device’s power good function, the TPS40100 can implement a sequential sequencing scheme, where a single power supply output voltage will ramp up and settle at its final regulation voltage before the next power supply voltage ramps up. By using a soft-start capacitor, the TPS40100 is able to implement a ratio-metric scheme that proportionally ramps up both power supply outputs at the same time until proper regulation is reached. Finally, the device can effectively implement a simultaneous sequencing scheme through its integrated amplifier.

Margining Control
In addition to supporting various sequencing implementations, the TPS40100 incorporates a simple margining control function that allows a power system designer to temporarily adjust the output voltage to a value either above or below the nominal regulation voltage. Two digital input pins allows the user to margin up or margin down the power supply by plus or minus five percent or plus or minus three percent. This feature enables a power supply manufacturer to verify a board’s compliant operation while at the limits of the power supply’s tolerance.

Increased Efficiency and Power Supply Protection
The TPS40100 efficiently manages power supplies up to 15 amps with peak efficiencies of 90 percent. In addition, the synchronous peak current mode controller with on-chip adaptive gate drive provides a peak current mode control loop, which allows simple compensation insensitive to wide variations of output capacitance. For improved load regulation, separate power ground and signal ground pins provide high accuracy remote load sensing.

The device is also equipped with all supervisory and control features for today’s power supplies, including pre-bias startup capability, programmable under-voltage lock out (UVLO), lossless DCR current sensing, power good indicator, synchronization input, programmable over-current protection and thermal shutdown.

Availability, Packaging and Pricing
The TPS40100 controller is available in volume from TI and its authorized distributors. Packaged in a 24-pin QFN, suggested resale pricing is $1.45 each in quantities of 1,000 units. TI’s easy-to-use TPS40K Designer Software for the TPS40100 will be available in the third quarter of 2005. Evaluation modules, application notes, reference designs and TI’s Power Management Selection Guide are available through power.ti.com.

Texas Instruments, Inc., 1-800-477-8924, www.ti.com

Among the more desirable features that TI calls attention to are the device’s toggle switch function for ordering up the ±5 and ±3 percent margining function, which provides a convenient means for "stressing" a system in a pre-test environment, i.e., before shipping the end equipment. The device’s current feedback control loop is designed to be very tight and virtually immune to unstable circuit operation caused by variations in output capacitance, a valuable attribute in situations where the required output capacitance is widely different from application to application. In addition, the device’s pre-bias start-up scheme holds off the synchronous rectifier until the device completes its soft-start operation.

But the crux of the comparison comes with TI focusing on six categories against one device the company sees as its strongest competitior—Linear Technology’s LTC3770. Comparisons of this nature can be useful or not, depending on the particular application to which the device is applied, so let the designer beware.

The categories includes dead-time, current-sense, current-limit and fault recovery, frequency of operation, under-voltage lockout (UVLO) functionality, and device packaging. The TPS40100’s dead-time is automatically adjustable, while the LTC3770’s is said to be fixed by the user to provide 70 ns. The TPS40100’s dead-time can go down to about half that value, according to the company. The TPS40100’s current-sense tool is its inductor resistance, while the LTC3770 uses an FET or resistor—which is either less accurate or incurs additional losses, according to TI.

TI’s device uses hiccup recovery in current-limiting. TI says that approach requires much less of a load reduction in order to restart; versus current-foldback limiting, used by the LTC3770. The TPS40100 can operate at a user adjustable frequency of 100 to 600 kHz, while the LTC3770’s output frequency is variable with line and load unless synchronized, says TI. The under-voltage lockout function in TI’s device is user programmable for level and hysteresis, while Linear’s device is fixed at 100 mV hysteresis. In addition, TI’s device measures 4-by-4 mm in a 24-pin package; Linear’s device is in a 5-by-5 mm package with 32 pins, or otherwise available in a 28-lead SSOP.

The device datasheet is available at //focus.ti.com/lit/ds/symlink/tps40100.pdf.