20

LM43602-Q1

SNVSA83C – APRIL 2015 – REVISED OCTOBER 2017

www.ti.com

Product Folder Links: LM43602-Q1

Submit Documentation Feedback

Copyright © 2015–2017, Texas Instruments Incorporated

Feature Description (continued)

7.3.12 Overcurrent and Short Circuit Protection

The LM43602-Q1 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 set blanking time. The HS switch current is

compared to the output of the error amplifier (EA) minus slope compensation every switching cycle. Refer to

Functional Block Diagram for more details. The peak current of the HS switch is limited by the maximum EA

output voltage minus the slope compensation at every switching cycle. The slope compensation magnitude at the

peak current is proportional to the duty cycle.

When the LS switch is turned on, the current going through it is also sensed and monitored. The LS switch is not

turned OFF at the end of a switching cycle if its current is above the LS current limit ILS-LIMIT. The LS switch is

kept ON so that inductor current keeps ramping down, until the inductor current ramps below the LS current limit.

Then the LS switch is then turned OFF, and the HS switch turned on, after a dead time. If the current of the LS

switch is higher than the LS current limit for 32 consecutive cycles and the power-good flag is low, hiccup current

protection mode is activated. In hiccup mode, the regulator is shut down and kept off for 5.5 ms typically before

the LM43602-Q1 tries to start again. If overcurrent or short-circuit fault condition still exists, hiccup repeats until

the fault condition is removed. Hiccup mode reduces power dissipation under severe overcurrent conditions,

prevents over heating and potential damage to the device.

Hiccup is only activated when power-good flag is low. Under non-severe overcurrent conditions when VOUT has

not fallen outside of the PGOOD tolerance band, the LM43602-Q1 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 power-good flag becomes low, hiccup operation starts

after LS current limit is tripped 32 consecutive cycles.

7.3.13 Thermal Shutdown

Thermal shutdown is a built-in self protection to limit junction temperature and prevent damages due to

overheating. Thermal shutdown turns off the device when the junction temperature exceeds 160°C typically to

prevent further power dissipation and temperature rise. Junction temperature reduces after thermal shutdown.

The LM43602-Q1 attempts to restart when the junction temperature drops to 150°C.

7.4 Device Functional Modes

7.4.1 Shutdown Mode

The EN pin provides electrical ON and OFF control for the LM43602-Q1. When VEN is below 0.4 V, the device is

in shutdown mode. Both the internal LDO and the switching regulator are off. In shutdown mode the quiescent

current drops to 2.3 µA typically with VIN = 24 V. The LM43602-Q1 also employs undervoltage lockout protection.

If VCC voltage is below the UVLO level, the output of the regulator is turned off.

7.4.2 Standby Mode

The internal LDO has a lower enable threshold than the regulator. When VEN is above 1.2 V and below the

precision enable falling threshold (1.8 V typically), the internal LDO regulates the VCC voltage at 3.2 V. The

precision enable circuitry is turned on once VCC is above the UVLO threshold. The switching action and voltage

regulation are not enabled unless VEN rises above the precision enable threshold (2.1 V typically).

7.4.3 Active Mode

The LM43602-Q1 is in active mode when VEN is above the precision enable threshold and VCC is above its UVLO

level. The simplest way to enable the LM43602-Q1 is to connect the EN pin to VIN. This allows self start-up when

the input voltage is in the operation range: 3.5 V to 36 V. Refer to Enable (EN) and VCC, UVLO, and BIAS for

details on setting these operating levels.