RT1 =

0.8 x RT2

VOUT2 - 0.8

TRACK

R

T2

R

T1

R

FB2

R

FB1

FB

V

OUT2

V

FB

LM5115A

Master

Power

Supply

V

SS

V

OUT1

VOUT1

VOUT2

3.3V

2.5V

LM25115A

www.ti.com

SNVS501B – FEBRUARY 2007 – REVISED APRIL 2013

Figure 14.

Figure 15.

Vphase = 10V

CH1 = Master output, 1V/Div

CH2 = COMP, 5/Div

CH3 = Iout, 1A/Div

CH4 = SSPR Output (Slave), 1V/Div

Horizontal Resolution= 200 µs/Div

Figure 16. Tracking with Equal Soft Start Time

Alternatively, the tracking feature can be used to create equal slew rates between the output voltages of the

master supply and the LM25115A. This method ensures that the output voltage of the LM25115A 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:

Again, a value of 10k

Ω 1% is recommended for RT2. For the case of VOUT1 = 3.3V and VOUT2 = 2.5V, RT1

should be 4.32 k

Ω 1%. The timing diagram and the waveforms for equal slew rates configuration are shown in

Figure 17 and Figure 18.

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