Datasheet

(LM3495)
(Master Supply)
V
OUT1
V
OUT2
0.6V = V
OUT2
R
T1
R
T1
+ R
T2
(LM3495)
(Master Supply)
V
OUT1
V
OUT2
0.65V = V
OUT1
R
T1
R
T1
+ R
T2
LM3495
SNVS410F –FEBRUARY 2006–REVISED APRIL 2013 www.ti.com
One way to use the tracking feature is to design the tracking resistor divider so that the master supply output
voltage (V
OUT1
) and the LM3495 output voltage (V
OUT2
) both rise together and reach their target values at the
same time. For this case, the equation governing the values of the tracking divider resistors R
T1
and R
T2
is:
(1)
The above equation is set equal to 0.65V in order to ensure that the final value of the track pin voltage exceeds
the reference voltage of the LM3495, and this 50 mV offset will cause the LM3495 output voltage to reach
regulation slightly before the master supply. A value of 10 kΩ 1% is recommended for R
T2
as a good
compromise between high precision and low quiescent current through the divider. If the master supply voltage
V
OUT1
is 5V, for example, then the value of R
T1
needed to give the two supplies identical soft start times would be
1.5 kΩ 1%. A timing diagram for this example, the equal soft start time case, is shown in Figure 31.
Figure 31. Tracking with Equal Soft Start Time
Alternatively, the tracking feature can be used to create equal slew rates between the output voltages of the
LM3495 and the master supply. This method ensures that the output voltage of the LM3495 always reaches
regulation before the output voltage of the master supply. In this case, the tracking resistors can be determined
based on the following equation:
(2)
Again, a value of 10 kΩ 1% is recommended for R
T2
. For the example case of V
OUT1
= 5V and V
OUT2
= 1.8V, R
T1
would be 5.62 kΩ 1%. A timing diagram for this example, the case of equal slew rates, is shown in Figure 32.
Figure 32. Tracking with Equal Slew Rates
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