LMZ14203H

www.ti.com

SNVS692G – JANUARY 2011 – REVISED OCTOBER 2015

Feature Description (continued)

NOTE

The DC current limit varies with duty cycle, switching frequency, and temperature.

7.3.3 Thermal Protection

The junction temperature of the LMZ14203H should not be allowed to exceed its maximum ratings. Thermal

protection is implemented by an internal Thermal Shutdown circuit which activates at 165 °C (typical) causing the

additionally the CSS capacitor is discharged to ground. Thermal protection helps prevent catastrophic failures for

accidental device overheating. When the junction temperature falls back below 145 °C (typical Hyst = 20 °C) the

7.3.4 Zero Coil Current Detection

The current of the lower (synchronous) MOSFET is monitored by a zero coil current detection circuit which

inhibits the synchronous MOSFET when its current reaches zero until the next ON-time. This circuit enables the

DCM operating mode, which improves efficiency at light loads.

7.3.5 Prebiased Startup

The LMZ14203H will properly start up into a prebiased output. This startup situation is common in multiple rail

logic applications where current paths may exist between different power rails during the startup sequence. The

prebias level of the output voltage must be less than the input UVLO set point. This will prevent the output pre-

bias from enabling the regulator through the high-side MOSFET body diode.

7.4 Device Functional Modes

7.4.1 Discontinuous Conduction and Continuous Conduction Modes

At light-load, the regulator will operate in discontinuous conduction mode (DCM). With load currents above the

critical conduction point, it will operate in continuous conduction mode (CCM). When operating in DCM the

switching cycle begins at zero amps inductor current; increases up to a peak value, and then recedes back to

zero before the end of the OFF-time. During the period of time that inductor current is zero, all load current is

supplied by the output capacitor. The next ON-time period starts when the voltage on the FB pin falls below the

internal reference. The switching frequency is lower in DCM and varies more with load current as compared to

CCM. Conversion efficiency in DCM is maintained since conduction and switching losses are reduced with the

smaller load and lower switching frequency.

Copyright © 2011–2015, Texas Instruments Incorporated

Submit Documentation Feedback

15

Product Folder Links: LMZ14203H