LM76005 datasheet(18/51 Pages) TI2

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6.3-V or higher capacitor for CBOOT. The VBOOT_UVLO threshold is typically 2.2 V. If the CBOOT capacitor is not

charged above this voltage with respect to SW, the device initiates a charging sequence using the low-side FET.

7.3.10 Power Good and Overvoltage Protection (PGOOD)

The LM76005 has a built-in power-good flag shown on the PGOOD pin to indicate whether the output voltage is

within its regulation level. The PGOOD signal can be used for start-up sequencing of multiple rails. The PGOOD

pin is an open-drain output that requires a pullup resistor to an appropriate logic voltage (any voltage below 12

V). The pin can sink 5 mA of current and maintain its specified logic low level. A typical range of pullup resistor

value is 10 kΩ to 100 kΩ. When the FB voltage is outside the power-good band, +6% above and –7% below the

internal reference VREF typically, the PGOOD switch is turned on, and the PGOOD pin voltage is pulled to

ground. When the FB is 2.5% (typical) closer to FB than the PGOOD threshold, the PGOOD switch is turned off,

and the pin is pulled up to the voltage connected to the pullup resistor. Both rising and falling edges of the

power-good flag have a built-in 140-µs (typical) deglitch delay. To pull up the PGOOD pin to a voltage higher

than 15 V, a resistor divider can be used to divide the voltage down.

PGT

PGB

PGOOD

Figure 7-8. PGOOD Resistor Divider

For given pullup voltage, VPU, the desired voltage on PGOOD pin, VPG, and RPGT chosen, use Equation 11 to

calculate RPGB:

PGB

PGT

(11)

7.3.11 Overcurrent and Short-Circuit Protection

The LM76005 is protected from overcurrent conditions by cycle-by-cycle current limiting on both peak and valley

of the inductor current. Hiccup mode is activated if a fault condition persists to prevent overheating.

High-side MOSFET overcurrent protection is implemented by the nature of the peak current-mode control. The

HS switch current is sensed when the HS is turned on after a blanking time. The HS switch current is compared

to either the minimum of a fixed current set point (IHS_Limit) or the output of the voltage regulation loop minus

slope compensation every switching cycle.

When the LS switch is turned on, the current going through it is also sensed and monitored. Before turning off

the LS switch at the end of every clock cycle, the LS current is compared to the LS current limit. If the LS current

limit is exceeded, the LS MOSFET stays on, and the HS switch is not turned on. The LS switch is kept ON so

that inductor current keeps ramping down, until the inductor current ramps below ILS_LIMIT. The LS switch is

turned off once the LS current falls below the limit, and the HS switch is turned on again after a dead time.

If the current of the LS switch is higher than the LS current limit for 128 consecutive cycles, and the feedback

voltage falls 60% below regulation, hiccup current-protection mode is activated. In hiccup mode, the regulator is

shut down and kept off for 40 ms typically before the LM76005 tries to start again. If overcurrent or a short-circuit

fault condition still exists, hiccup repeats until the fault condition is removed. Hiccup mode reduces power

dissipation under severe overcurrent conditions, and prevents overheating and potential damage to the device.

Under non-severe overcurrent conditions when the feedback voltage has not fallen 60% below regulation, the

LM76005 reduces the switching frequency and keeps the inductor current valley clamped at the LS current limit

level. This operation mode allows slight overcurrent operation during load transients without tripping hiccup.

If tracking was used for initial sequencing, the device attempts to restart using the internal soft-start circuit until

the tracking voltage is reached.

LM76005

SNVSBK5A – FEBRUARY 2020 – REVISED JULY 2020

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