Datasheet

LMR12010
V
IN
V
IN
EN
BOOST
SW
FB
GND
V
OUT
C3
L1
C2
R1
R2
D1
ON
OFF
D2
D3
C1
R3
LMR12010
V
IN
V
IN
EN
BOOST
SW
FB
GND
V
OUT
C3
L1
C2
R1
R2
D1
D2
ON
OFF
C1
R3
LMR12010
SNVS731A –SEPTEMBER 2011–REVISED SEPTEMBER 2011 www.ti.com
Figure 25. V
BOOST
Derived from V
IN
Figure 26. V
BOOST
Derived from Series Zener Diode (V
OUT
)
Enable Pin / Shutdown Mode
The LMR12010 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 30nA. Switch leakage
adds another 40nA from the input supply. The voltage at this pin should never exceed V
IN
+ 0.3V.
SOFT-START
This function forces V
OUT
to increase at a controlled rate during start up. During soft-start, the error amplifier’s
reference voltage ramps from 0V to its nominal value of 0.8V in approximately 200µs. This forces the regulator
output to ramp up in a more linear and controlled fashion, which helps reduce inrush current. Under some
circumstances at start-up, an output voltage overshoot may still be observed. This may be due to a large output
load applied during start up. Large amounts of output external capacitance can also increase output voltage
overshoot. A simple solution is to add a feed forward capacitor with a value between 470pf and 1000pf across
the top feedback resistor (R1).
Output Overvoltage Protections
The overvoltage comparator compares the FB pin voltage to a voltage that is 10% higher than the internal
reference Vref. Once the FB pin voltage goes 10% above the internal reference, the internal NMOS control
switch is turned off, which allows the output voltage to decrease toward regulation.
Undervoltage Lockout
Undervoltage lockout (UVLO) prevents the LMR12010 from operating until the input voltage exceeds 2.74V(typ).
The UVLO threshold has approximately 440mV of hysteresis, so the part will operate until V
IN
drops below
2.3V(typ). Hysteresis prevents the part from turning off during power up if V
IN
is non-monotonic.
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