LMZ10501SH datasheet(12/25 Pages) TI

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LMZ10501

SNVS677D – MAY 2011 – REVISED MARCH 2013

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OVERVIEW

The LMZ10501 SIMPLE SWITCHER® nano module is an easy-to-use step-down DC-DC solution capable of

driving up to 1A load in space-constrained applications. Only an input capacitor, an output capacitor, a small

VCON filter capacitor, and two resistors are required for basic operation. The nano module comes in 8-pin POS

footprint package with an integrated inductor. The LMZ10501 operates in fixed 2.0MHz PWM (Pulse Width

Modulation) mode, and is designed to deliver power at maximum efficiency. The output voltage is typically set by

using a resistive divider between the built-in reference voltage VREF and the control pin VCON. The VCON pin is the

positive input to the error amplifier. The output voltage of the LMZ10501 can also be dynamically adjusted

between 0.6V and 3.6V by driving the VCON pin externally. Internal current limit based softstart function, current

overload protection, and thermal shutdown are also provided.

CIRCUIT OPERATION

The LMZ10501 is a synchronous Buck power module using a PFET for the high side switch and an NFET for the

synchronous rectifier switch. The output voltage is regulated by modulating the PFET switch on-time. The circuit

generates a duty-cycle modulated rectangular signal. The rectangular signal is averaged using a low pass filter

formed by the integrated inductor and an output capacitor. The output voltage is equal to the average of the duty-

cycle modulated rectangular signal. In PWM mode, the switching frequency is constant. The energy per cycle to

the load is controlled by modulating the PFET on-time, which controls the peak inductor current. In current mode

control architecture, the inductor current is compared with the slope compensated output of the error amplifier. At

the rising edge of the clock, the PFET is turned ON, ramping up the inductor current with a slope of (VIN -

VOUT)/L. The PFET is ON until the current signal equals the error signal. Then the PFET is turned OFF and

NFET is turned ON, ramping down the inductor current with a slope of VOUT /L. At the next rising edge of the

clock, the cycle repeats. An increase of load pulls the output voltage down, resulting in an increase of the error

signal. As the error signal goes up, the peak inductor current is increased, elevating the average inductor current

and responding to the heavier load. To ensure stability, a slope compensation ramp is subtracted from the error

signal and internal loop compensation is provided.

INPUT UNDER VOLTAGE DETECTION

The LMZ10501 implements an under voltage lock out (UVLO) circuit to ensure proper operation during startup,

shutdown and input supply brownout conditions. The circuit monitors the voltage at the VIN pin to ensure that

sufficient voltage is present to bias the regulator. If the under voltage threshold is not met, all functions of the

controller are disabled and the controller remains in a low power standby state.

SHUTDOWN MODE

To shutdown the LMZ10501, pull the EN pin low (<0.5V). In the shutdown mode all internal circuits are turned

OFF.

EN PIN OPERATION

The EN pin is internally pulled up to VIN through a 790kΩ (typ.) resistor. This allows the nano module to be

enabled by default when the EN pin is left floating. In such cases VIN will set EN high when VIN reaches 1.2V. As

the input voltage continues to rise, operation will start once VIN exceeds the under-voltage lockout (UVLO)

threshold. To set EN high externally, pull it up to 1.2V or higher. Note that the voltage on EN must remain at less

than VIN+ 0.2V due to absolute maximum ratings of the device.

INTERNAL SYNCHRONOUS RECTIFICATION

The LMZ10501 uses an internal NFET as a synchronous rectifier to minimize the switch voltage drop and

increase efficiency. The NFET is designed to conduct through its intrinsic body diode during the built-in dead time

between the PFET on-time and the NFET on-time. This eliminates the need for an external diode. The dead time

between the PFET and NFET connection prevents shoot through current from VIN to PGND during the switching

transitions.

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