CS1613 datasheet(9/17 Pages) APEX

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CS1610/11/12/13

DS929F5

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 133A.

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





--------------------------------------------------------------------

[Eq.1]

RIPK

4000000

IPK code



-----------------------

[Eq.2]

VBST

CS1610 /11/12/13

15k

ADC

RBST

IBSTOUT

Iref

BSTOUT

RBST

VBST

Iref

--------------

400V

133

A

------------------





[Eq.3]

RIAC

IAC

Vrect

CS1610 /11/12/13

15k

ADC

Iref

RIAC

RBST

[Eq.4]

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