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DC-DC powers advanced multi-rail digital chipsets

A Summit Microelectronics product story
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Edited by the Electronicstalk editorial team Feb 4, 2011

Summit's SMB109 programmable DC-DC is ideal for powering advanced multi-rail digital chipsets in a range of communications, computing and consumer applications.

This includes notebook/netbook/tablet, server/storage, telecom/datacom and multimedia devices.

Summit's SMB109 simplifies complex power design challenges by integrating multiple DC-DC outputs with digital power management/monitoring and non-volatile system configuration, reducing component count, cost, size and time to market.

The SMB109's high power-conversion efficiency, output-voltage control and advanced power-down modes facilitate 'Green' and Energystar-compliant design.

With a serial digital interface and on-board non-volatile memory, the SMB109 can be easily configured during development and re-programmed in-system by host software.

The result is a flexible, digitally controlled power-supply design that is easily customisable without repetitive hardware design cycles or complex microcontroller-style GPIO-based control.

The integration of advanced power-control functions eliminates external components and cost, improves functionality and performance, and minimises development time.

The SMB109 integrates eight outputs, three buck controllers, one LDO controller and four load-switch controllers with a digital I2C interface.

The current-mode buck controllers accept inputs from 4.5 to 28V and the output voltage can be digitally programmed from 0.5 to 5V (or higher with external resistor divider) in 10mV steps with one per cent regulation accuracy.

Depending on the output MOSFET's used, each buck output can support over 20A continuous output current.

Switching frequency is programmable from 300 to 1,200kHz to optimize size versus efficiency, while the three buck outputs are interleaved by 120deg to reduce current ripple and noise.

Pulse-skipping mode is supported (with fixed frequency PWM override) to optimise conversion efficiency during light-load operation.

The LDO controller controls an external Nchannel MOSFET up to 5A+ and also has a programmable output voltage of 0.5 to 5V.

In addition to the four main buck and LDO outputs, the SMB109 integrates four load-switch controllers.

These outputs control external FETs as load switches to control power to loads separately from the main outputs.

For example, if there are two loads in the system that use the same voltage but need to be enabled, soft-started, sequenced or monitored separately, this can accomplished by powering the 'primary' load directly from the main output and powering the 'subordinate' load through the load switch.

The output drive for the load-switch controllers is powered by an internal charge pump up to +10V, allowing the use of low-cost, low-Rds-on-Nchannel MOSFETs.

The advantage of this integrated main output/load switch output architecture is that it allows seamless system integration and eliminates the expense and board space of redundant DC-DC converters.

The integrated digital control block tightly integrates power management for all outputs, including the main outputs and the load-switch controllers.

All outputs are controlled for enable/sequencing by either the internal auto-sequencer, register enable bits or pin control.

Each of the EN pins can be independently programmed to assign output-channel control, making it easy to implement any combination of automatic or host-controlled start-up.

Output voltage is set in 10 or 20mV steps between 0.5V and 5V with static or dynamic (on-the-fly) programming.

All eight outputs have programmable duration softstart, eliminating the worry of inrush current and the associated cost of extra output decoupling capacitors.

The load-switch outputs have their own feedback path, enabling closed-loop control.

Also, all outputs are independently monitored for under-/over-voltage/over-current conditions, with programmable thresholds and Powergood/Reset policy making complete system monitor and reset design very simple and robust.

Short-circuit protection is also programmable, with selectable, sequence down, 'hard' shutdown or crowbar response for each output channel with automatic 'hiccup mode' soft restart.

The SMB109 also protects itself against over-temperature with thermal shutdown protection.

Another feature of the SMB109 is independent real-time voltage/current/power monitor.

This monitor is comprised of an 8-bit analogue-to-digital converter that measures input voltage and current, and stores the values in a register that can be accessed via the I2C interface.

This integrated function enables automated system power diagnostics to speed up debugging, system validation and characterisation without the expense and design effort of a custom telemetry circuit.

If not needed in production, the circuit can be disabled with no loss in performance or cost impact.

Compact 7 x 7mm QFN-56 packaging and minimal external components yield a small solution size for ease of implementation on dense PCBs.

Programmed configuration is held in the OTP non-volatile memory but may be changed in system by host software via the I2C port.

The rated operating temperature range is -40 to 85C.

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Company Summit Microelectronics

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