Delta Electronics DNS SIP Series User Manual

Page 11

8.2.6 Voltage Tracking

The DNS family was designed for applications that have output voltage tracking requirements
during power-up and power-down. The devices have a TRACK pin to implement three types
of tracking method: sequential, ratio-metric and simultaneous. TRACK simplifies the task of
supply voltage tracking in a power system by enabling modules to track each other, or any
external voltage, during power-up and power-down.

By connecting multiple modules together, customers can get multiple modules to track their
output voltages to the voltage applied on the TRACK pin.

Detailed Description

Sequential Implementation

Sequential start-up is implemented by connecting the power good signal (PWRGD pin) of PS1
to the TRACK pin of PS2 with a resistor–capacitor (RC) circuit. The waveforms of power up
and down are in Figures 4 and 5. In Figure 4, the 5V PS1 supply ramps up first. When supply
reaches its final 5V steady state value, the open collector output of the PWRGD pin releases
to the TRACK pin and the PS2 output voltage rises at the rate of the RC time constant. In
Figure 5, the PWRGD pin pull low by PS1 ENABLE off or the PS1 output voltage is below 90%
of the desired regulated voltage, and then the TRACK pin is pulled low and the PS2 power
down. Figure 3 shows the circuit diagram of sequential start-up when Vo

PS2

tracks the

PWRGD of PS1.

TRACK

PS1

PS2

PS1

Vin

PWRGD

ENABLE

Figure 3. PS1 and PS2 track output voltage Sequential start-up