LMR12007 Datasheet, PDF (10/30 Pages) Texas Instruments – LMR12007 Thin SOT23 750mA Load Step-Down DC-DC Regulator

LMR12007
SNVS982 – SEPTEMBER 2013
I_BOOST = 0.49 x (0.5 + 0.54) x (5 - 0.7) mA = 2.19mA
R3 = (10V - 5V) / (1.4 x 2.19mA + 1mA) = 1.23kΩ
V_Z
C4 D3
D2
R3
V_IN
C_IN
V_IN
BOOST
SW
GND
V_BOOST
C_BOOST
L
D1
V_OUT
C_OUT
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Figure 23. Boost Voltage Supplied from the Shunt Zener on V_IN
ENABLE PIN / SHUTDOWN MODE
The LMR12007 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 1.25V in approximately 200µs. This forces the regulator
output to ramp up in a more linear and controlled fashion, which helps reduce inrush current.
OUTPUT OVERVOLTAGE PROTECTION
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 LMR12007 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.
CURRENT LIMIT
The LMR12007 uses cycle-by-cycle current limiting to protect the output switch. During each switching cycle, a
current limit comparator detects if the output switch current exceeds 1.5A (typ), and turns off the switch until the
next switching cycle begins.
THERMAL SHUTDOWN
Thermal shutdown limits total power dissipation by turning off the output switch when the IC junction temperature
exceeds 165°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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