Cirrus Logic AN368 - Manual (Page 49)

AN368
AN368REV2 49
9. Configure the second-stage dim level adjustment using the external temperature. The external NTC
connected to the eOTP pin is used to measure the temperature.To enable the adjustment process, bit
DIM_TEMP in register Config58 at Address 90 is set to ‘1’.
10. Set the lower saturation limit for the 8-bit temperature code provided to the color system from the fast
low-pass filter before it is used for polynomial computations.The lower saturation limit CODE
LOWSAT
is
calculated using bits LOW_SAT[2:0] in register Config58 at Address 90 and Equation 80.
11. Sets the higher saturation limit CODE
HISAT
for the 8-bit temperature code provided to the color system
before it is used for polynomial computations. The higher saturation limit CODE
HISAT
is determined by
bits HI_SAT[2:0] in register Config59 at Address 91.
k. Internal Overtemperature Protection
Internal overtemperature protection (iOTP) is used to monitor the die temperature of the CS1630. The device
uses a digital algorithm that detects iOTP events using the iOTP settings configured in the following steps:
1. The internal overtemperature protection feature is enabled when bit IOTP is set to ‘0’. Bit IOTP is bit 0
in register Config47 at Address 79.
2. Configure the sample rate of the internal temperature sensor when the IC is not in an iOTP fault state.
Set bit IOTP_SAMP in register Config48 at Address 80 to ‘0’ for a fast sample rate or to ‘1’ for a slow
sample rate (recommended).
Step 16) Clamp Circuit
To keep dimmers conducting and prevent them from misfiring, a minimum power needs to be delivered from
the dimmer to the load. This power is nominally around 2W for 230V and 120V TRIAC dimmers. At low dim
angles (≤ 90°), this excess power cannot be converted into light by the output stage because of dim mapping
at light loads. V
BST
can rise above the safe operating voltage of the primary-side bulk capacitor C6. The clamp
circuit drains excess charge from capacitor C6 by turning ‘ON’ transistor Q3, dissipating the power into load
resistors R11 and R9. The clamp load resistors R11 and R9 must each be 2k
 2W resistors for 230V systems
and 500  2W resistors for 120V systems.
Step 17) Designing the EMI Filter
The switching frequency of the CS1630 can cause resonance in the EMI filter, so it is important to carefully
design it. Resonance can cause undue noise and oscillation and can impact power factor. The resonant
frequencies on the LC filters must be less than 1/10 of the minimum switching frequency of the boost stage.
There is a variety of dimmers, and each behaves differently. All dimmers are sensitive to the presence of heavy
EMI filters with a large capacitance or inductance. Capacitance on the AC side of the rectifier should be
avoided. Capacitance to the immediate output of the rectifier bridge should be minimized for optimal dimmer
compatibility.
HI_SAT[2:0] CODE
HISAT
0 CODE
TEMPShutdown
1 100
2 120
3 140
4 160
5 180
6 200
7 220
Table 8. High Saturation Limit
CODE
LOWSAT
LOW_SAT[2:0]
 1  + 5  =
[Eq. 80]