LM749x0-Q1 supports low IQ SLEEP mode operation. This mode can be enabled by pulling SLEEP pin low (EN = High). In SLEEP mode, device turns off internal charge pump, SW switch and disables DGATE and HGATE drive thus achieving low current consumption of 6-μA typical. However at the same time device power up always on loads connected on OUT pin through an internal low power MOSFET with typical on resistance of 7 Ω. In this mode device can support peak load current of 100 mA. As load is increased, voltage drop across internal MOSFET increases. Device offers overcurrent protection during sleep mode with typical overcurrent threshold of 250 mA. In case of overcurrent event during sleep mode, device protects internal FET by disconnecting the internal MOSFET switch and latching off the device. As an additional layer of protection, device also features thermal shutdown with latch off feature in SLEEP mode in case of any overheating of the device in SLEEP mode. To put the device out of the latch mode user has to toggle the SLEEP or EN pin.

In SLEEP mode LM749x0-Q1 offers protection against input overvoltage events. Device can be configured in either overvoltage cut-off (SLEEP_OV connected to C) or overvoltage clamp mode (SLEEP_OV connected to VOUT) with default overvoltage threshold of 21-V typical.

If SLEEP mode feature is not required then SLEEP pin should be tied to EN. When not used SLEEP_OV pin can be left floating.

Figure 9-10 LM749x0-Q1 SLEEP Mode Operation

A higher overvoltage threshold for SLEEP mode can be achieved by adding an external Zener diode between SLEEP_OV pin to OUT/C as shown in Figure 9-11. This feature is useful while configuring overvoltage threshold for 24-V or 48-V powered systems.

Figure 9-11 Increasing SLEEP_OV Threshold Using an External Zener Diode