TPS54341_15 datasheet(14/48 Pages) TI

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ENA

UVLO2

START

ENA

UVLO1

START

STOP

UVLO1

HYS

Vout

0.8V

= R

0.8 V

´ ç

TPS54341

SLVSC61 – NOVEMBER 2013

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DETAILED DESCRIPTION (continued)

Error Amplifier

A transconductance error amplifier controls the TPS54341 device voltage-regulation loop. The error amplifier

compares the FB pin voltage to the lower of the internal soft-start voltage or the internal 0.8-V voltage reference.

The transconductance (gm) of the error amplifier is 350

μA/V during normal operation. During soft-start

operation, the transconductance is reduced to 78

μA/V and the error amplifier is referenced to the internal soft-

start voltage.

The frequency compensation components (capacitor, series resistor, and capacitor) are connected between the

error amplifier output COMP pin and GND pin.

Adjusting the Output Voltage

The internal voltage reference produces a precise 0.8-V ±1% voltage reference over the operating temperature

and voltage range by scaling the output of a bandgap-reference circuit. The output voltage is set by a resistor

divider from the output node to the FB pin. Using 1% tolerance or better divider resistors is recommended. Select

the low-side resistor RLS for the desired divider current and use Equation 2 to calculate RHS. To improve

efficiency at light loads consider using larger value resistors. However, if the values are too high, the regulator is

more susceptible to noise and voltage errors from the FB input current may become noticeable.

(2)

Enable and Adjusting Undervoltage Lockout

The TPS54341 device enables when the VIN pin voltage rises above 4.3 V and the EN pin voltage exceeds the

enable threshold of 1.2 V. The TPS54341 device disables when the VIN pin voltage falls below 4 V or when the

EN pin voltage is below 1.2 V. The EN pin has an internal pullup-current source, I1, of 1.2 μA that enables

operation of the TPS54341 device when the EN pin floats.

If an application requires a higher undervoltage-lockout (UVLO) threshold, use the circuit shown in Figure 26 to

adjust the input-voltage UVLO with two external resistors. When the EN pin voltage exceeds 1.2 V, an additional

3.4

μA of hysteresis current, IHYS, is sourced out of the EN pin. When the EN pin pulls below 1.2 V, the 3.4-μA

IHYS current is removed. This additional current facilitates adjustable input-voltage UVLO hysteresis. Use

Equation 3 to calculate RUVLO1 for the desired UVLO hysteresis voltage. Use Equation 4 to calculate RUVLO2 for

the desired VIN start voltage.

In applications designed to start at relatively low input voltages (that is, from 4.5 o 9 V) and withstand high input

voltages (for example, 40 V), the EN pin can experience a voltage greater than the absolute maximum voltage of

8.4 V during the high-input voltage condition. To avoid exceeding this voltage when using the EN resistors, the

EN pin is clamped internally with a 5.8-V Zener diode capable of sinking up to 150

μA.

(3)

(4)

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