LM76002 datasheet(21/59 Pages) TI2

21 / 59 page

PGB

PGT

PGB

PGOOD

LM76002, LM76003

www.ti.com

SNVSAK0A – OCTOBER 2017 – REVISED OCTOBER 2019

Product Folder Links: LM76002 LM76003

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Figure 20. PGOOD Resistor Divider

For given pullup voltage VPU and desired voltage on PGOOD pin is VPG and with RPGT chosen, value for RPGB

can be calculated using Equation 14:

(14)

7.3.12 Overcurrent and Short-Circuit Protection

The LM76002/LM76003 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 the either the minimum of a fixed current set point (ISC) or the output of the voltage regulation loop minus slope

compensation every switching cycle. The slope compensation increases with duty cycle and tends to lower the

HS current limit above 60% duty cycle as it lowers below ISC. See Typical Characteristics.

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 ILSLIMIT. 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 LM76002/LM76003 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 LM76002/LM76003 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.

7.3.13 Thermal Shutdown

Thermal shutdown limits total power dissipation by turning off the internal switches when the device junction

temperature exceeds 160°C (typical). After thermal shutdown occurs, hysteresis prevents the device from

switching until the junction temperature drops to approximately 135°C. When the junction temperature falls below

135°C, the LM76002/LM76003 attempts to soft start.

LM76002 Datasheet(PDF) 21 Page - Texas Instruments

LM76002 Datasheet(HTML) 21 Page - Texas Instruments

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