Datasheet

Using the Evaluation Hardware

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6.4 Buck and EN_T Control

The Control/Status Bits Control menu controls the following aspects of the chip:

1. Temp – Reflects the status of the regulators. If a buck or LDO regulator falls out of regulation because

of the temperature, it will be shown in that panel.

2. System Delay Sequence – Allows for the user to program a preset delay sequence for the startup of

the chip.

3. Enable ext clock for bucks – If checked, the user must input a 13MHz clock to the SYNC pin of the

IC. If unchecked, the bucks will run internally with a 2MHz clock.

4. Spread Spectrum, SS modulation – May help to reduce noise from the buck switchers. Described in

detail in the “Spread Spectrum” section off the LP3907 datasheet.

5. Bypass UVLO – This option disables the Under-Voltage Lock Out feature, which automatically

disables the regulators when the supply is less than 2.8V.

6. POR Delay– This option sets the delay time of the Power-On Reset function. More details can be

found in the “Flexible Power-On Reset” section of the datasheet.

Figure 9. Interrupt Control Interface

7 Using the Evaluation Hardware

7.1 Powering the LP3907 Board

We recommend that the user power the LP3907 through an external power supply if any loads are

attached to the regulators. In case no external power supply is available (as for showroom purposes), the

USB interface can be used to power the chip.

7.1.1 External supply

The LP3907 Evaluation board can be powered using a battery or wall adapter as described in previous

sections. Simply apply the voltage to the VDD_M pin referenced to GND_M.

Before applying power to VDD_M, be sure to disconnect the USBPOWER jumper. Failure to do so

may damage the USB chip and/or the IC. Full functionality of the GUI will still be available if powered by

an external power supply.

Also note that if the supply to VDD_M is close to 2.8V with a heavy load current on the regulators, the chip

is in danger of powering down due to UVLO. To disable UVLO, check the “Bypass UVLO” feature.

7.1.2 USB Interface Supply

In case the external supply or battery is not available, the USB board can be used to power the LP3907

chip. Simply connect the USBPOWER jumper to the 5V pin on the LP3907 evaluation board.

NOTE: External power supplies should be DISCONNECTED from the VDD_M pin if powering from

the USB.

The USB interface card can provide the following voltages :

• 5V from USB interface (default setting) -- USBPOWER needs to be set to 5V

• 3.3V -- USBPOWER needs to be set to 3.3V. Useful if the user wants to provide a lower voltage to the

AN-1619 Evaluation Kit for LP3907 — Programmable Power Management SNVA233A–September 2007–Revised April 2013

Unit with 1

C Compatible Interface

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