Digital Power Regulators Strive For Simplicity

Aug. 3, 2006
The 25-A ZL2005 digital-control point-of-load (POL) converter now has a baby brother. Zilker Laboratories' 3-A ZL2105 seamlessly interfaces with the ZL2005, but it also integrates its own power MOSFETs (RDS(ON) = 120 mΩ) and boost diode. It's desig

The 25-A ZL2005 digital-control point-of-load (POL) converter now has a baby brother. Zilker Laboratories' 3-A ZL2105 seamlessly interfaces with the ZL2005, but it also integrates its own power MOSFETs (RDS(ON) = 120 mΩ) and boost diode. It's designed to work alongside one or more ZL2005s (see the figure).

Zilker's claim to fame isn't that it closesthe voltage-regulation loop in the digital domain, though the fact that the company does it with a state machine is significant. Also, the resulting ±1% regulation precision is impressive. The really interesting differentiator is how simple it is to use multiple ZL controllers in the same circuit.

These controllers can be individually programmed (pin-strap, resistor, or SMBus) for regulated output voltage, turn-on delay, and output voltage ramp rate. SMBus programming provides the highest precision, but simply using a pair of resistors allows the output to be positioned between 0.6 and 5.5 V in 10-mV steps.

Alternatively, simple pin-strapping (three pins, low, high, or open) enables the output voltage to be set to any of nine values between 0.6 and 5 V.

For power sequencing, a group of ZL2005 and ZL2105 devices may be configured to power up in a predetermined order by issuing PMBus commands to assign preceding and succeeding devices in the sequencing chain.

Yet a simpler approach would use Zilker's patented autonomous sequencing mode since no I2C/SMBus host is needed. All that's necessary is that the I2C pins on each device be interconnected. Sequence order is determined on the basis of each device's I2C/SMBus address.

Members of the group turn on in order, starting with the device with the lowest address and continuing through until all devices in the chain are on. No device starts its turn-on routine until the previous device is in regulation. The device with the highest address will turn off first, followed in reverse order by the other devices in the group.

Phase-spreading is possible when all converters are synchronized to the same switching clock. In that case, the phase offset for each chip is determined by its device address, where phase offset = device address X 45°.

Thus, a device address of 0x00 or 0x20 would configure no phase offset. A device address of 0x01 or 0x21 would configure 45° of phase offset, and a device address of 0x02 or 0x22 would configure 90° of phase offset. Or, the phase offset of each device could be set to any value between 0° and 337.5° in 22.5° increments via the I2C/SMBus interface.

A system controller can monitor ZL2005/ZL2105 system parameters, including input and output voltages, output current, switching frequency and duty cycle, and internal junction temperature or the temperature of an external device through the bus interface. The chips can be set to independently monitor for fault conditions and signal the controller via a separate pin when those fault conditions occur.

The ZL2105's input voltage range is 4.5 to 14 V and its output range is 0.6 to 5.5 V at up to 3 A continuous. Measured with a 12-V input and a 3.3-V output, efficiency is greater than 90%. Switching frequencies may range from 200 kHz to 2 MHz.

As with the ZL2005, tools on Zilker's Web site let engineers optimize their designs and verify the performance before they order. Sampling now, the ZL2105 comes in a 6- by 6-mm micro lead-frame (MLF) package. Pricing starts at $4.25 in lots of 1000.

Zilker Laboratories

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