Low power mode (LPM) is designed to be able to still provide small amounts of current to loads without consuming much quiescent current. This type of feature is useful in power-at-all-time loads or to just generally reduce the amount of power dissipation from the supply. The quiescent current draw during this mode is defined in Section 5.5 under I_Q,LPM. The TPS4HC120-Q1 can automatically enter and exit this mode by detecting that the load current is below I_LPM,enter on all active channels, and then exits this mode when load current increases above I_LPM,exit. This section describes the entry, exit and protections mechanisms in this mode.

Entry into LPM

When the load current going through the channel is below the I_LPM,enter threshold on all active channels and diagnostics are turned off (DIAG_EN is low) for longer than t_STBY, the device automatically enters into LPM. This means that the digital core is turned off and the charge pump strength is reduced to reduce the quiescent current to I_Q,LPM.

All the requirements below need to be met for the device to enter the LPM automatically:

• T_J < 125°C
• V_BB ≥ 6V
• DIAG_EN is LOW
• At least one channel is ON
• All the ON channels have load currents < I_LPM,enter per channel
• No EN pin toggling
• All the above conditions are true for time longer than t_STBY

Figure 6-2 Entering LPM

During LPM

The quiescent current of the device during LPM, I_Q,LPM, is a function of how many channels are active and is proportional to the load current meaning that the lower the load current during this time, the lower the quiescent current is. Additionally, since the digital core is disabled, the diagnostics like current sensing or open load detection are not available during this mode. If diagnostics are desired, the DIAG_EN pin can be enabled to exit LPM and return the part back to normal operation. Once DIAG_EN is disabled the device goes back into LPM after t_STBY. Similarly, the current limit mechanism is not active in the same manner as by definition the minimum current limit is higher than the entry point of LPM. However, the short-circuit protection will still be in place to protect the device.

Below is the summary of the behavior of the device during LPM:

• I_q reduces to I_Q,LPM per channel
• R_DS,ON per channel increases to R_DSON,LPM
• No clamped current limit for overload conditions as the device will exit the LPM first
• Short-circuit protection is in place to shut off the device if load current increases to I_PKLPM,exit during LPM
• No thermal shutdown protection

Exiting LPM

The device exits LPM if any of four conditions is met:

• Load current increases slowly: If the load current increases beyond I_LPM,exit slowly, the device wakes up and pulls the LPM pin low to signal the device is no longer in low power mode. The output votlage droop is minimal.
  Figure 6-3 Exiting LPM With Load Current Slow Increase
• Load current increases rapidly (short-circuit): If the load current increases rapidly beyond I_LPM,exit, the device shuts down to protect itself and come back on within the t_WAKE time in normal operation with full functionality. As the part comes back on, LPM pin is pulled LOW to represent that the part has come out of LPM. The FLT pin will also be pulled low is the fault is still present.
  Figure 6-4 Exiting LPM With Rapid Load Current Increase (Short-Circuit)
• Any ENx is toggled (from ON to OFF or OFF to ON): If any channel is turned ON or turned OFF during LPM, the device wakes up and perform the desired action. After the device wakes up, if the LPM entry conditions are still met, the part enters LPM again after t_STBY.
• DIAG_EN is turned ON: if DIAG_EN goes high, the device goes into the DIAGNOSTIC mode which fully turns on the part so that all of the functionality works as intended in the DIAGNOSTIC state. If DIAG_EN goes back low, with all LPM entry conditions are met, the part goes back into LPM after t_STBY.

Any time the device comes out of LPM to ACTIVE state, the LPM pin is pulled LOW. If the system needs to wake up when the device comes out of LPM, the LPM pin can be used to send a wake up signal to the MCU. Otherwise the LPM pin can be ignored.