LMZ10500

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SNVS723F – OCTOBER 2011 – REVISED FEBRUARY 2015

Feature Description (continued)

Since the output current is limited during normal startup by the softstart function, the current charging the output

reaching 0.375 V at the end of the startup sequence. In such cases the module will maintain the described above

hiccup mode and the output voltage will not ramp up to final value. To cause this condition, one would have to

use unnecessarily large output capacitance for 650mA load applications. See the Input and Output Capacitor

Selection section for guidance on maximum capacitances for different output voltage settings.

7.3.4 Thermal Overload Protection

The junction temperature of the LMZ10500 should not be allowed to exceed its maximum operating rating of

125°C. Thermal protection is implemented by an internal thermal shutdown circuit which activates at 150°C (typ).

When this temperature is reached, the device enters a low power standby state. In this state switching remains

requiring maximum output current may require derating at elevated ambient temperature. See the Typical

Characteristics section for thermal derating plots for various output voltages.

7.4 Device Functional Modes

7.4.1 Circuit Operation

The LMZ10500 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

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.

7.4.2 Input Undervoltage Detection

The LMZ10500 implements an under voltage lock out (UVLO) circuit to ensure proper operation during startup,

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.

7.4.3 Shutdown Mode

To shutdown the LMZ10500, pull the EN pin low (< 0.5 V). In the shutdown mode all internal circuits are turned

OFF.

7.4.4 EN Pin Operation

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

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

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