Datasheet

LM25117
LM25117-Q1
SNVS714E –APRIL 2011–REVISED MARCH 2013 www.ti.com
Maximum Duty Cycle
When operating with a high PWM duty cycle, the high-side NMOS device is forced off each cycle for 320ns to
ensure that C
HB
is recharged and to allow time to sample and hold the current in the low-side NMOS FET. This
forced off-time limits the maximum duty cycle of the controller. When designing a regulator with high switching
frequency and high duty cycle requirements, a check should be made of the required maximum duty cycle
against the graph shown in Figure 31. The actual maximum duty cycle varies with the switching frequency as
follows:
Figure 31. Maximum Duty Cycle vs Switching Frequency
Thermal Protection
Internal thermal shutdown circuitry is provided to protect the controller in the event the maximum junction
temperature is exceeded. When activated, typically at 165°C, the controller is forced into a low power shutdown
mode, disabling the output drivers and the VCC regulator. This feature is designed to prevent overheating and
destroying the device.
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