Datasheet

t
t
DO
VV +
t
t
t
v
'
IN
V
( )
tsw
V
L
i
V
IN
-V
OUT
-
D
V
( )
tL
V
( )
tL
I
( )
tDIODE
I
( )
tCapacitor
I
( )
tOUT
V
S
T
S
DT
OUT
- i
( )
-
L
i
OUT
- i
LMR62421
SNVS734B –OCTOBER 2011–REVISED APRIL 2013 www.ti.com
Figure 14. Typical Waveforms
CURRENT LIMIT
The LMR62421 uses cycle-by-cycle current limiting to protect the internal NMOS switch. It is important to note
that this current limit will not protect the output from excessive current during an output short circuit. The input
supply is connected to the output by the series connection of an inductor and a diode. If a short circuit is placed
on the output, excessive current can damage both the inductor and diode.
Design Guide
ENABLE PIN / SHUTDOWN MODE
The LMR62421 has a shutdown mode that is controlled by the Enable pin (EN). When a logic low voltage is
applied to EN, the part is in shutdown mode and its quiescent current drops to typically 80 nA. Switch leakage
adds up to another 1 µA from the input supply. The voltage at this pin should never exceed V
IN
+ 0.3V.
THERMAL SHUTDOWN
Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature
exceeds 160°C. After thermal shutdown occurs, the output switch doesn’t turn on until the junction temperature
drops to approximately 150°C.
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