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| LM3463_12 Datasheet, PDF (20/40 Pages) Texas Instruments – LM3463 Dynamic Headroom Controller with Thermal Control Interface and Individual Channel Dimming Control | |||
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LM3463
SNVS807 â MAY 2012
VRAIL
VRAIL(peak)
VDHC_READY
VRAIL(steady)
VRAIL(nom)
www.ti.com
0
Initiated by
primary power
supply
Pushed up
by LM3463
DHC activated
Time
Figure 7. Changes of VRAIL during system startup
Shortening System Startup Time
The system startup time can be shortened by sinking current from the ISR pin to ground through a resistor, RISR.
The lower resistance the RISR carries, the shorter time the system startup takes. Sinking current from the ISR pin
increases the charging current to the capacitor, CDHCand eventually increases the rate of the increasing of VRAIL
during startup (VRAIL ramps up from VRAIL(nom) to VDHC_READY). Figure 8 shows how the system startup time is
shortened by using different value of RISR.
VRAIL
tST-1
tST-2
tST-3
VDHC_READY
VLED
VRAIL(nom)
VIN-UVLO
6.67V
0
Startup time
tST-1
tST-2
tST-3
RISR
open
high
low
Time
Figure 8. Setting different startup time using different RISR
Generally, the system startup time tST is the longest when the ISR pin is left open (tST-1). The amount of the
decreasing of the startup time is inversely proportional to the current being drawn from the ISR pin, thus
determined by the value of the resistor, RISR. The rate of decreasing of the startup time is governed by the
following equation.
20
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Copyright © 2012, Texas Instruments Incorporated
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