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APW7158 Datasheet(PDF) 14 Page - Anpec Electronics Coropration |
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APW7158 Datasheet(HTML) 14 Page - Anpec Electronics Coropration |
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14 / 24 page  Copyright © ANPEC Electronics Corp. Rev. A.2 - Aug., 2009 APW7158 www.anpec.com.tw 14 Function Description Soft-Start/Enable Shunt Regulator The APW7158 must have two power supplies V CC (5V) and V CC12 (12V) to drive the IC; VCC (5V) is for the control circuits and V CC12 (12V) is for the drivers of outputs. The shunt regulator is designed for these systems like figure 3 that do not have a 5V power supply; the range of the shunt regulator voltage (5.8V, typical) is designed over the usual range 4.5V to 5.5V of typical 5V power supplies. Connect a resistor from VCC12 pin to VCC pin for shunt regulator and for the supply current; the typical value, 300 Ω of the resistor is recommended. Phase Shift The device offers 180 °phase shift function between OUT1 and OUT2. The advantage of Phase shift is to avoid over- lapping the switching current spikes of the two channels or interaction between the channels; it also reduces the RMS current of the input capacitors, allowing fewer caps to be employed. However, because the phase shift be- tween the rising edge of V LGATE1 and VLGATE2 (See Figure 1.) depends on the duty cycles, the falling edges of the two channels might overlap. Therefore, the user should check it. Figure 1. Phase of V LGATE2 with respect to rising edge of V LGATE1 0 o 180 o VUGATE 1 VLGATE 1 VUGATE 2 VLGATE 2 The SS/EN pins control the soft-start and enable or dis- able the controller. The two regulators have independent soft-start and enable functions. Connect a soft-start ca- pacitor from each SS/EN pin to the GND to set the soft- start interval, and an open drain logic signal for each SS/ EN pin will enable or disable the respective output. Figure 2 shows the soft-start interval. When both V CC and V CC12 reach their Power-On-Reset threshold 4.23V and 7.8V, a 30 µA current source starts to charge the capacitor. When the V SS reaches the enabled threshold about 1V, the internal 0.6V reference starts to rise and follows the V SS; the error amplifier output (VCOMP) suddenly raises to 1.1V, which is the valley of the oscillator’s triangle wave, and leads the V OUT to start up. Until the V SS reaches about 3.0V, the internal reference completes the soft-start interval and reaches to 0.6V, and then V OUT is in regulation. The VSS still rises to 3.5V and then stops. TIME VOLTAGE t1 t2 t0 VSS/EN VOUT 3V 1V Figure 2. Soft-Start Interval V 2 I C t t T SS SS 1 2 START SOFT ⋅ = − = − Where: C SS = external Soft-Start capacitor I SS = Soft-Start current = 30µA |
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