Datasheet

t
RT
=
8 x 3V x C
T
6PA
t
CBT
=
4V x C
T
240PA
t
IDT
=
4V x C
T
6 PA
LM5068
www.ti.com SNVS254C –JANUARY 2004–REVISED MARCH 2013
The typical operating ranges of under-voltage and over-voltage thresholds are calculated from the above
equations with known resistors. For example, for resistor values: R1=130KΩ, R2=5.5KΩ, and R3=4.5KΩ, the
computed thresholds are:
• UV turn-on = 37.60V
• UV turn-off = 35.0V
• OV turn-off = 77.78V
• OV turn-on = 75.07V
To maintain the threshold's accuracy, a resistor tolerance of 1% or better is recommended.
Calculation of Normal, Circuit Breaker, and Retry Timing
The C
T
capacitor at the TIMER pin controls the timing functions of the LM5068. When the interlock conditions are
met the timer capacitor is charged to 4V in a slow initial delay time period t
IDT
calculated from:
(5)
If the SENSE pin detects more than 50mV across R
S
, the TIMER pin charges C
T
with 240µA. The Circuit
Breaker timeout period t
CBT
is calculated from:
(6)
When the LM5068-2 or LM5068-4 is latched, it pulls down the GATE pin and initiates eight, 6µA charging cycles
between 1V and 4V on C
T
. The total re-try time period t
RT
is given by:
(7)
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