TPS65279V datasheet(22/46 Pages) TI

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TPS65279V

SLVSBW1B – FEBRUARY 2013 – REVISED JANUARY 2014

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DETAILED DESCRIPTION

Adjusting the Output Voltage

The output voltage is set with a resistor divider from the output node (VOUT) to the FB pin. It is recommended to

use 1% tolerance or better divider resistors.

Figure 41. Voltage Divider Circuit

(1)

Start with a 40.2-k

Ω for R1 and use Equation 1 to calculate R2. To improve efficiency at light loads consider

using larger value resistors. If the values are too high, the regulator is more susceptible to noise and voltage

errors from the FB input current are noticeable.

Output voltage can also be changed by I2C controlled VID in a 7-bit register.

The minimum output voltage and maximum output voltage can be limited by the minimum on time of the high-

side MOSFET and bootstrap voltage (BOOT-PH voltage) respectively. More discussions are located in Minimum

Output Voltage and Bootstrap Voltage (BOOT) and Low Dropout Operation.

Enable and Adjusting Under-Voltage Lockout

The EN pin provides electrical on/off control of the device. Once the EN pin voltage exceeds the threshold

voltage, the device starts operation. If the EN pin voltage is pulled below the threshold voltage, the regulator

stops switching and enters low Iq state.

The EN pin has an internal pull-up current source, allowing the user to float the EN pin for enabling the device. If

an application requires controlling the EN pin, use open drain or open collector output logic to interface with the

pin.

The device implements internal UVLO circuitry on the VIN pin. The device is disabled when the VIN pin voltage

falls below the internal VIN UVLO threshold. The internal VIN UVLO threshold has a hysteresis of 500mV.

If an application requires either a higher UVLO threshold on the VIN pin or a secondary UVLO on the PVIN, in

split rail applications, then the EN pin can be configured as shown in Figure 42.

When using the external UVLO function it is recommended to set the hysteresis to be greater than 500 mV.

The EN pin has a small pull-up current IP which sets the default state of the pin to enable when no external

components are connected. The pull-up current is also used to control the voltage hysteresis for the UVLO

function since it increases by Ih once the EN pin crosses the enable threshold. The UVLO thresholds can be

calculated using Equation 2 and Equation 3.

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