STANDBY

SHUTDOWN

BOOST STARTUP

NORMAL MODE

STARTUP

1) TSD = L

TSD = H

or

UVLO = H

EN = H

X_EN = H

1

EN = L

TIME OUT

LM3549

SNVS640A – AUGUST 2010 – REVISED MAY 2013

www.ti.com

Modes of Operation

Figure 4. Modes of Operation

SHUTDOWN: Shutdown mode is entered always if EN is low or internal Power On Reset (POR) is active. Power

on reset will activate during the chip startup or when the supply voltage VDD falls below 1.5V. This is the

low power consumption mode, when all circuit functions are disabled.

STARTUP: When EN input is pulled high, the internal startup sequence powers up all the needed internal blocks

(VREF, Oscillator, etc.). EEPROM values are also read to registers during Startup.

STANDBY: After Startup device enters Standby mode. In standby mode all support blocks are active but buck-

boost converter and the drivers are disabled. Control registers can be written in this mode and the control

bits are effective immediately. EEPROM writing is allowed only in standby mode.

BOOST STARTUP: Soft start for boost output is generated in the boost startup mode. The boost output is raised

in a low current mode. Soft start time can be set with registers. The boost startup is entered from Standby

if any of the X_EN inputs is pulled high.

NORMAL: During normal mode user controls the chip using the X_EN inputs. In normal mode buck-boost

converter and drivers are active. Device returns to standby mode if all X_EN inputs are low for time period

set by Time out register. If EN input is pulled low device goes to shutdown mode.

TSD: If the chip temperature rises too high, the thermal shutdown (TSD) disables the chip operation and

Standby mode is entered until no thermal shutdown event is present.

6

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