(LM3495)

(Master Supply)

VOUT1

VOUT2

0.6V = VOUT2

RT1

RT1 + RT2

(LM3495)

(Master Supply)

VOUT1

VOUT2

0.65V = VOUT1

RT1

RT1 + RT2

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 (VOUT1) and the LM3495 output voltage (VOUT2) 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 RT1 and RT2 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 k

Ω 1% is recommended for RT2 as a good

compromise between high precision and low quiescent current through the divider. If the master supply voltage

VOUT1 is 5V, for example, then the value of RT1 needed to give the two supplies identical soft start times would be

1.5 k

Ω 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 k

Ω 1% is recommended for RT2. For the example case of VOUT1 = 5V and VOUT2 = 1.8V, RT1

would be 5.62 k

Ω 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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