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CS1612 Fiches technique(PDF) 9 Page - Cirrus Logic |
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CS1612 Fiches technique(HTML) 9 Page - Cirrus Logic |
9 / 17 page CS1610/11/12/13 DS929F5 9 5.4 Boost Stage The high-voltage FET in the source-follower startup circuit is source-switched by a variable current source on the SOURCE pin to operate a boost circuit. Peak FET switching current is set with an external resistor on pin IPK. In No-Dimmer Mode, the boost stage begins operating when the start threshold is reached during each rectified half line-cy- cle and is disabled at the nominal boost output voltage. The peak FET switching current determines the percentage of the rectified input voltage conduction angle over which the boost stage will operate. The control algorithm adjusts the peak FET switching current to maximize the operating time of the boost stage, thus improving the input power factor. When operating in Leading-edge Dimmer Mode, the boost stage ensures the hold current requirement of the dimmer is met from the initiation of each half-line dimmer conduction cycle until the peak of the rectified input voltage. Trailing-edge Dimmer Mode boost stage ensures that the trailing-edge is exposed at the correct time with the correct current. 5.4.1 Maximum Peak Current The maximum boost inductor peak current is set using an external resistor, RIPK, on pin IPK, which is sampled periodically by an ADC. Maximum power output is proportional to IPK(code). See Equation 1: where, = correction term = 0.55 Vrms, typical = nominal operating input RMS voltage IPK(BST) =IPK(code) x4.1mA The external resistor, RIPK, is calculated using the peak current code, IPK(code). See Equation 2: 5.4.2 Output BSTOUT Sense & Input IAC Sense A current proportional to the boost output voltage, VBST, is supplied to the IC on pin BSTOUT and is used as a feedback control signal. The ADC is used to measure the magnitude of the IBSTOUT current through resistor RBST. The magnitude of the IBSTOUT current is then compared to an internal reference current (Iref) of 133A. Figure 9. BSTOUT Input Pin Model Resistor RBST sets the feedback current at the nominal boost output voltage. For the CS1611/13, RBST is calculated as shown in Equation 3: where, VBST = Nominal boost output voltage Iref = Internal reference current For 120VAC line voltage applications (CS1610/12), nominal boost output voltage, VBST, is 200V, and resistor RBST is 1.5M. By using digital loop compensation, the voltage feedback signal does not require an external compensation network. A current proportional to the AC input voltage is supplied to the IC on pin IAC and is used by the boost control algorithm. Figure 10. IAC Input Pin Model Resistor RIAC sets the IAC current and is defined in Equation 4: For optimal performance, RIAC and RBST should use 1% or better resistors for best VBST voltage accuracy. 5.4.3 Boost Auxiliary Winding The boost auxiliary winding is used for zero-current detection (ZCD). The voltage on the auxiliary winding is sensed through the BSTAUX pin of the IC. It is also used to deliver current during steady-state operation, as mentioned in section 5.2 Startup Circuit on page 8. Pin max , I PK BST Vrms typical , 2 -------------------------------------------------------------------- = [Eq.1] RIPK 4000000 IPK code ----------------------- = [Eq.2] VBST CS1610 /11/12/13 15k ADC R8 RBST IBSTOUT R9 Iref 16 BSTOUT 12 RBST VBST Iref -------------- 400V 133 A ------------------ 3M == [Eq.3] R3 RIAC IAC I AC Vrect CS1610 /11/12/13 15k ADC R4 2 Iref 12 RIAC RBST = [Eq.4] |
Numéro de pièce similaire - CS1612 |
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Description similaire - CS1612 |
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