CS1601-FSZ datasheet(12/16 Pages) CIRRUS

12 / 16 page

CS1601

DS931PP6

table below depicts approximate values for R3 and R4 for a

range of boost-to-auxiliary inductor turns ratio, N.

Table 1. Aux Inductor Turns Ratio vs. R3 and R4

Resistors R3 and R4 were calculated using Vlink = 460V and

Cp =10pF.

Equation 6 is used to calculate the cut-off frequency defined

by the RC circuit at the ZCD pin.

where:

The cut-off frequency, fc, needs to be 10x the ringing

frequency.

Capacitance at the ZCD pin

5.8 Brownout Protection

The CS1601 brownout detection circuit monitors the peak of

the Vrect input voltage and disables the PWM switching when

it drops below a pre-determined threshold. Hysteresis and

minimum detection time are provided to avoid brownout

detection during short input transients. When brownout is

detected, the CS1601 enters standby mode. On recovery from

brownout, it re-enters normal operating mode.

Current IAC is proportional to the AC input voltage Vrect,where

Vrect =RIACxIACand RIAC = R1+R2 in Figure 19 on page 11.

The digitized current applied to the IAC pin is monitored by the

brownout protection algorithm. When Vrect drops below the

brownout detection threshold, the CS1601 triggers a timer.

The IC asserts the brownout protection and stops the gate-

drive switching only if the timer exceeds 56ms. This is the

equivalent of 7 rectified line cycles at 60Hz.

During the brownout state, the device continues monitoring

the input line voltage. The device exits the brownout state

when IAC exceeds the brownout upper threshold for at least

56ms. Typical values for the lower (IBP(lower)) and upper

(IBP(upper)) brownout thresholds are 31.6A and 39.6A,

respectively.

The overpower protection may activate prior to brownout

protection, depending on the load.

Figure 22. Brownout Sequence

The maximum response time of the brownout protection

feature occurs at light-load conditions. It is calculated by

Equation 7.

where:

VBP(th) Brownout threshold voltage, VBP(th) = IBP(lower)xRIAC

5.9 Overvoltage Protection

The overvoltage protection (OVP) will trigger immediately and

stop the gate drive when the current into the IFB pin (IOVP)

exceeds 105% of the reference current (Iref) value. The IC

resumes gate drive switching when the measured current at IFB

drops below IOVP –IOVP(Hy). Equation 8 is used to calculate the

OVP threshold (VOVP).

5.10 Overcurrent Protection

To limit boost inductor current through the FET and to prevent

boost inductor saturation conditions, the CS1601 incorporates

a cycle-by-cycle peak inductor current limit circuit using an

external shunt resistor to ‘sense’ the FET source current

accurately. The overcurrent protection (OCP) circuit is

designed to monitor the current when the active switch is

turned on. The OCP circuit is enabled after the leading-edge

blanking time (tLEB). The shunt voltage is compared to a

reference voltage, Vcs(th), to determine whether an

overcurrent condition exists. The OCP circuit triggers

immediately, allowing the OCP algorithm to turn off the gate

driver.

The overcurrent protection circuit is also designed to monitor

for a catastrophic overcurrent occurrence by sensing sudden

and abnormal operating currents. A second OCP threshold,

Vcs(clamp), determines whether a severe overcurrent condition

exists. This immediately turns off the gate drive and the

system enters a restart mode. The CS1601 inhibits all

switching operations for approximately 1.6ms then attempts to

restart normal operation.

N~R3

~R4

946k



1.75k



42k



1.75k



37.5k



1.75k



35.5k



1.75k



32k



1.75k



29.5k



1.75k



27.5k



1.75k



 R3 R4



C





[Eq.6]

56 ms

Start

Timer

Enter Standby

Exit Standby

Upper

Lower

Brownout

Thresholds

Start Timer

TBrownout

8ms

------------ 128 V VBP th



–

 56 ms

[Eq.7]

--- 128 94.8

–

 56

117ms

VOVP

RIFB IOVP



VDD

[Eq.8]

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