LMR14003, LMR14006

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SNVSA10 – NOVEMBER 2013

Enable (/SHDN) and VIN Under Voltage Lockout

LMR14003/6 /SHDN pin is a high voltage tolerant input with an internal pull up circuit. The device can be enabled

even if the /SHDN pin is floating. The regulator can also be turned on using 1.23V or higher logic signals. If the

use of a higher voltage is desired due to system or other constraints, a 100k

Ω or larger resistor is recommended

between the applied voltage and the /SHDN pin to protect the device. When /SHDN is pulled down to 0V, the

chip is turned off and enters the lowest shutdown current mode. In shutdown mode the supply current will be

decreased to approximately 1µA. If the shutdown function is not to be used the /SHDN pin may be tied to VIN.

The maximum voltage to the SHDN pin should not exceed 40V. LMR14003/6 has an internal UVLO circuit to

shutdown the output if the input voltage falls below an internally fixed UVLO threshold level. This ensures that

the regulator is not latched into an unknown state during low input voltage conditions. The regulator will power up

when the input voltage exceeds the voltage level. If there is a requirement for a higher UVLO voltage, the /SHDN

can be used to adjust the input voltage UVLO by using external resistors.

Current Limit

The LMR14003/6 implements current mode control which uses the internal COMP voltage to turn off the high

side MOSFET on a cycle-by-cycle basis. Each cycle the switch current and internal COMP voltage are

compared, when the peak switch current intersects the COMP voltage, the high side switch is turned off. During

overcurrent conditions that pull the output voltage low, the error amplifier will respond by driving the COMP node

high, increasing the switch current. The error amplifier output is clamped internally, which functions as a switch

current limit.

Overvoltage Transient Protection

The LMR14003/6 incorporates an overvoltage transient protection (OVTP) circuit to minimize voltage overshoot

when recovering from output fault conditions or strong unload transients on power supply designs with low value

output capacitance. For example, when the power supply output is overloaded the error amplifier compares the

actual output voltage to the internal reference voltage. If the FB pin voltage is lower than the internal reference

voltage for a considerable time, the output of the error amplifier will respond by clamping the error amplifier

output to a high voltage. Thus, requesting the maximum output current. Once the condition is removed, the

regulator output rises and the error amplifier output transitions to the steady state duty cycle. In some

applications, the power supply output voltage can respond faster than the error amplifier output can respond, this

actuality leads to the possibility of an output overshoot. The OVTP feature minimizes the output overshoot, when

using a low value output capacitor, by implementing a circuit to compare the FB pin voltage to OVTP threshold

which is 108% of the internal voltage reference. If the FB pin voltage is greater than the OVTP threshold, the

high side MOSFET is disabled preventing current from flowing to the output and minimizing output overshoot.

When the FB voltage drops lower than the OVTP threshold, the high side MOSFET is allowed to turn on at the

next clock cycle.

Thermal Shutdown

The device implements an internal thermal shutdown to protect itself if the junction temperature exceeds

170°C(typ). The thermal shutdown forces the device to stop switching when the junction temperature exceeds

the thermal trip threshold. Once the junction temperature decreases below 160°C(typ), the device reinitiates the

power up sequence.

Copyright © 2013, Texas Instruments Incorporated

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