LMZ14201TZ-ADJ NSC [National Semiconductor], LMZ14201TZ-ADJ Datasheet - Page 10

• Manufacturer Part Number: LMZ14201TZ-ADJ
• Manufacturer: NSC [National Semiconductor]

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Application Block Diagram
COT Control Circuit Overview
Constant On Time control is based on a comparator and an
on-time one shot, with the output voltage feedback compared
with an internal 0.8V reference. If the feedback voltage is be-
low the reference, the main MOSFET is turned on for a fixed
on-time determined by a programming resistor R
connected to V
input supply voltage. Following this on-time, the main MOS-
FET remains off for a minimum of 260 ns. If the voltage on the
feedback pin falls below the reference level again the on-time
cycle is repeated. Regulation is achieved in this manner.
Design Steps for the LMZ14201
Application
The LMZ14201 is fully supported by Webench® and offers
the following: Component selection, electrical and thermal
simulations as well as the build-it board for a reduction in de-
sign time. The following list of steps can be used to manually
design the LMZ14201 application.
IN
Current Limit 3.3V
such that on-time is reduced with increasing
OUT
@ 25°C
30114654
ON
. R
ON
is
10
• Select minimum operating V
• Program V
• Program turn-on time with soft-start capacitor selection
• Select C
• Select C
• Set operating frequency with R
• Determine module dissipation
• Layout PCB for required thermal performance
ENABLE DIVIDER, R
The enable input provides a precise 1.18V band-gap rising
threshold to allow direct logic drive or connection to a voltage
divider from a higher enable voltage such as V
input also incorporates 90 mV (typ) of hysteresis resulting in
a falling threshold of 1.09V. The maximum recommended
voltage into the EN pin is 6.5V. For applications where the
midpoint of the enable divider exceeds 6.5V, a small zener
can be added to limit this voltage.
The function of this resistive divider is to allow the designer to
choose an input voltage below which the circuit will be dis-
O
IN
O
Current Limit 3.3V
with divider resistor selection
ENT
AND R
IN
with enable divider resistors
OUT
ON
ENB
@ 85°C
30114608
SELECTION
30114668
IN
. The enable