Datasheet

V
IN
Time
V
SW
Time
V
SYNC
t
SY_SW
V
IH_SYNC
V
IL_SYNC
LM21212-1
www.ti.com SNVS671E –FEBRUARY 2011–REVISED MARCH 2013
OPERATION DESCRIPTION
GENERAL
The LM21212-1 switching regulator features all of the functions necessary to implement an efficient low voltage
buck regulator using a minimum number of external components. This easy to use regulator features two
integrated switches and is capable of supplying up to 12A of continuous output current. The regulator utilizes
voltage mode control with trailing edge modulation to optimize stability and transient response over the entire
output voltage range. The device can operate at high switching frequency allowing use of a small inductor while
still achieving high efficiency. The precision internal voltage reference allows the output to be set as low as 0.6V.
Fault protection features include: current limiting, thermal shutdown, over voltage protection, and shutdown
capability. The device is available in the HTSSOP-20 package featuring an exposed pad to aid thermal
dissipation. The LM21212-1 can be used in numerous applications to efficiently step-down from a 5V or 3.3V
bus.
FREQUENCY SYNCHRONIZATION
The sync (SYNC) pin allows the LM21212-1 to be switched at an external clock frequency. When a clock signal
is present on the SYNC pin within the allowable frequency range, 300 kHz to 1.5 MHz, the device will
synchronize the turn-on of the high side FET (switch rising) to the negative edge of the clock signal, as seen in
Figure 25 . If no clock signal is present, the LM21212-1 will default to a switching frequency of 1 MHz. The clock
signal can be present on the SYNC pin before the device is powered on with no loading on the clock signal.
Alternatively, if no clock is present while the device is powered up, it will begin switching at the default frequency
of 1 MHz. Once the clock signal is present, the device will begin synchronizing to the clock frequency. The length
of time necessary for the synchronization depends on the clock frequency.
Figure 25. Frequency synchronization
PRECISION ENABLE
The enable (EN) pin allows the output of the device to be enabled or disabled with an external control signal.
This pin is a precision analog input that enables the device when the voltage exceeds 1.35V (typical). The EN pin
has 110 mV of hysteresis and will disable the output when the enable voltage falls below 1.24V (typical). If the
EN pin is not used, it can be left open, and will be pulled high by an internal 2 µA current source. Since the
enable pin has a precise turn-on threshold it can be used along with an external resistor divider network from VIN
to configure the device to turn-on at a precise input voltage.
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