LM5166DRCT datasheet(23/57 Pages) TI2

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Temperature (qC)

-50

-25

100

125

150

160

170

180

190

200

D014

VFB (V)

0.2

0.4

0.6

0.8

0.2

0.4

0.6

0.8

1.2

D013

8.1 t

LM5166

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SNVSA67B – DECEMBER 2016 – REVISED JUNE 2017

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CSS is discharged by an internal 80-Ω FET when VOUT is shutdown by EN, UVLO, or thermal shutdown.

It is desirable in some applications for the output voltage to reach its nominal setpoint in the shortest possible

time. Connecting a 100-kΩ resistor from SS to GND disables the soft-start circuit of the LM5166, and the

LM5166 operates in current limit during start-up to rapidly charge the output capacitance.

Diode emulation mode (DEM) of the LM5166 prevents negative inductor current enabling monotonic start-up

under prebiased output conditions. With a prebiased output voltage, the LM5166 waits until the soft-start ramp

allows regulation above the prebiased voltage and then follows the soft-start ramp to the regulation setpoint as

shown in Figure 46 and Figure 47.

Time Scale: 2 ms/Div

CH1: VEN, 1 V/Div

CH2: VOUT, 1 V/Div

CH4: IOUT, 200 mA/Div

Figure 46. ENABLE On and Off; VOUT Prebiased to 1.8 V

Figure 52 Circuit, VIN = 24 V, No Load

Time Scale: 2 ms/Div

CH1: VEN, 5 V/Div

CH2: VOUT, 1 V/Div

CH4: IOUT, 200 mA/Div

Figure 47. ENABLE On and Off; VOUT Prebiased to 1.8 V

Figure 52 Circuit, VIN = 24 V, 500 mA Load

7.3.9 Short-Circuit Operation

The LM5166 features a clamping circuit that clamps the SS voltage about 175 mV above the FB voltage (see

Figure 48 and Figure 49). The circuit is enabled in COT mode and only works when an external soft-start

capacitor is connected.

Figure 48. Soft-Start (SS) Voltage vs Feedback (FB)

Voltage

Figure 49. Soft-Start to Feedback Clamp Offset vs

Temperature

LM5166DRCT Datasheet(PDF) 23 Page - Texas Instruments

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