LM5176PWPR datasheet(17/45 Pages) TI2

17 / 45 page

Applying the appropriate voltage to the MODE pin of the LM5176 enables hiccup mode fault protection (see

Section 7.4.2). In hiccup mode, the controller shuts down after detecting cycle-by-cycle current limiting for 128

consecutive cycles and the soft-start capacitor is discharged. The soft-start capacitor is automatically released

after 4000 oscillator clock cycles and the controller restarts. If hiccup mode protection is not enabled through the

MODE pin, the LM5176 will operate in cycle-by-cycle current limiting as long as the overload condition persists.

7.3.6 Average Input/Output Current Limiting

The LM5176 provides optional average current limiting capability to limit either the input or the output current of

the DC/DC converter. The average current limiting circuit uses an additional current sense resistor connected in

series with the input supply or output voltage of the converter. A current sense gm amplifier with inputs at the

ISNS(+) and ISNS(-) pins monitors the voltage across the sense resistor and compares it with an internal 50-mV

reference. If the drop across the sense resistor is greater than 50 mV, the gm amplifier gradually discharges

the soft-start capacitor. When the soft-start capacitor discharges below the feedback reference voltage, VREF,

the output voltage of the converter decreases to limit the input or output current. The average current limiting

feature can be used in applications requiring a regulated current from the input supply or into the load. The target

constant current is given by Equation 4:

CL(AVG)

SNS

50 mV

(4)

A filter network as shown in Figure 8-1 is often used across the ISNS(+) and ISNS(-) pins to filter the ripple in the

average current sense signal.

The average current loop can be disabled by shorting the ISNS(+) and ISNS(-) pins together to AGND.

7.3.7 Operation Above 40-V Input

For application where input voltage is higher than 40 V, a 2-kΩ resistor in series with the VISNS pin is required

as shown in Figure 8-1.

7.3.8 CCM Operation

The LM5176 works in continuous conduction mode (CCM). In CCM operation, the inductor current can flow

in either direction and the controller switches at a fixed frequency regardless of the load current. The CCM

operation is useful for noise-sensitive applications where a fixed switching eases filter design.

7.3.9 Frequency and Synchronization (RT/SYNC)

The LM5176 switching frequency can be programmed between 100 kHz and 600 kHz using a resistor from the

RT/SYNC pin to AGND. The RT resistor is related to the nominal switching frequency (Fsw) by Equation 5:

190 ns

116 pF

(5)

Figure 6-3 in the Section 6.6 shows the relationship between the programmed switching frequency (Fsw) and the

RT resistor.

The RT/SYNC pin can also be used to synchronize the internal oscillator to an external clock signal. The

external synchronization pulse is ac coupled using a capacitor to the RT/SYNC pin. The external synchronization

pulse frequency range is 75% to 125% of the resistor programmed frequency. A 50% duty cycle is acceptable for

external SYNC.

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LM5176

SNVSAI1D – JUNE 2017 – REVISED AUGUST 2021

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