Datasheet

V
IN
Time
V
SW
Time
V
SYNC
t
SY_SW
V
IH_SYNC
V
IL_SYNC
LM21215A
www.ti.com SNOSB87B –MARCH 2011–REVISED MARCH 2013
OPERATION DESCRIPTION
GENERAL
The LM21215A-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 15A 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 eTSSOP-20 package featuring an exposed pad to aid thermal
dissipation. The LM21215A-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 LM21215A-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 LM21215A-1 will default to a switching frequency of 500 kHz. 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 500 kHz. 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.
UVLO
The LM21215A-1 has a built-in under-voltage lockout protection circuit that keeps the device from switching until
the input voltage reaches 2.7V (typical). The UVLO threshold has 200 mV of hysteresis that keeps the device
from responding to power-on glitches during start up. If desired the turn-on point of the supply can be changed
by using the precision enable pin and a resistor divider network connected to VIN as shown in Figure 30 in the
design guide.
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