(LM3495)

(Master Supply)

(LM3495)

(Master Supply)

LM3495

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SNVS410E – FEBRUARY 2006 – REVISED NOVEMBER 2007

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

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

1.5 k

Ω 1%. A timing diagram for this example, the equal soft start time case, is shown in Figure 3.

Figure 3. 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

would be 5.62 k

Ω 1%. A timing diagram for this example, the case of equal slew rates, is shown in Figure 4.

Figure 4. Tracking with Equal Slew Rates

FPWM MODE OPERATION

The LM3495 operates under forced PWM when the FPWM pin is connected to ground. While in FPWM

operation, the LM3495 controls the output voltage by adjusting the duty cycle of the power FETs with trailing

edge PWM. The output inductor and capacitor filter the square wave produced as the power FETs chop the input

voltage, thereby creating a regulated output voltage. The DC level of the output voltage can be set anywhere

from 0.6V up to 5.5V, and is determined by a pair of feedback resistors using the following equation:

(3)

Copyright © 2006–2007, Texas Instruments Incorporated

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