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LM5109A

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SNVS412C – APRIL 2006 – REVISED SEPTEMBER 2016

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9 Power Supply Recommendations

The recommended bias supply voltage range for LM5109A is from 8 V to 14 V. The lower end of this range is

governed by the internal undervoltage lockout (UVLO) protection feature of the VDD supply circuit blocks. The

upper end of this range is driven by the 18-V absolute maximum voltage rating of the VDD. TI recommends

keeping a 4-V margin to allow for transient voltage spikes.

The UVLO protection feature also involves a hysteresis function. This means that once the device is operating in

normal mode, if the VDD voltage drops, the device continues to operate in normal mode as long as the voltage

drop does not exceed the hysteresis specification, VDDH. If the voltage drop is more than hysteresis specification,

the device shuts down. Therefore, while operating at or near the 8-V range, the voltage ripple on the auxiliary

power supply output must be smaller than the hysteresis specification of LM5109A to avoid triggering device-

shutdown.

A local bypass capacitor must be placed between the VDD and GND pins. And this capacitor must be located as

close to the device as possible. A low-ESR, ceramic surface mount capacitor is recommended. TI recommends

using 2 capacitors across VDD and GND: a 100-nF, ceramic surface-mount capacitor for high-frequency filtering

placed very close to VDD and GND pin, and another surface-mount capacitor, 220-nF to 10-µF, for IC bias

requirements. In a similar manner, the current pulses delivered by the HO pin are sourced from the HB pin.

Therefore a 22-nF to 220-nF local decoupling capacitor is recommended between the HB and HS pins.