CS1631-FSZ datasheet(13/56 Pages) APEX

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CS1630/31

DS954F2

5.3.4 Leading-edge Mode

In Leading-edge Mode, the CS1630/31 regulates boost output

voltage VBST while maintaining the dimmer phase angle (see

Figure 9). The device executes a CCM boost algorithm using

dimmer attach current as the initial peak current for the initial

firing event of the dimmer. Upon gaining control of the incoming

current, the CS1630/31 transitions to a CRM boost algorithm to

regulate VBST. The device periodically executes a probe event

on the incoming waveform. The information from the probe

event is used to maintain proper operation with the dimmer

circuitry.

Figure 9. Leading-edge Mode Phase-cut Waveform

5.3.5 Trailing-edge Mode

In Trailing-edge Mode, the CS1630/31 determines its operation

based on the falling edge of the input voltage waveform (see

Figure 10). To provide proper dimmer operation, the

CS1630/31 executes the boost algorithm on the falling edge of

the input line voltage that maintains a charge in the dimmer

capacitor. To ensure maximum compatibility with dimmer

components, the device boosts during this falling edge event

using a peak current that must meet a minimum value. In

Trailing-edge Mode, only the CRM boost algorithm is used.

Figure 10. Trailing-edge Mode Phase-cut Waveform

5.4 Correlated Color Temperature Control

The CS1630/31 color control system can adjust and maintain

the correlated color temperature (CCT) for the LED color-

mixing application by connecting an external negative

temperature coefficient (NTC) thermistor to the eOTP pin. The

LED temperature variation can be accurately detected by the

internal eOTP feedback loops (see "External Overtemperature

Protection" on page 19).

Red and amber LEDs are necessary components in color-

mixing applications when providing warm white or other CCTs.

When mixing colors, red and amber LEDs are the most

temperature sensitive, so they cause a large variation in

temperature. The CS1630/31 is capable of providing LED

CCT and luminosity with temperature compensation using the

NTC thermistor to resolve the significant change in the

luminous output due to temperature variations.

Since LED lumens are mainly a function of temperature and

forward current, color temperature and luminosity can be

maintained by independently adjusting each string's output

current as the ambient temperature changes. This can be

done by mapping the NTC reading to a required value of the

current in each string using a digital mapping block.

In the CS1630/31, only one of the LED string currents is

compensated for due to temperature variations. The current in

the other string is kept constant over temperature, which may

result in the luminosity decreasing slightly as temperature

increases. In order for the ADC to resolve the entire range of

possible temperature variation in the LEDs, it is recommended

to select series resistor RS and NTC resistor RNTC with the

appropriate Beta value, which retains the total resistance

(RS+RNTC) at all possible operating temperatures within the

tracking range of the ADC. The final temperature-to-digital

code mapping depends on these variables.

The CS1630/31 color control system also has the ability to

maintain a constant CCT or change CCT as the light dims.

OTP configurations allow the selection of the dimming profile.

A specific CCT profile can be programmed to the digital

mapping device. In this case, the mapping is two-dimensional:

one current versus temperature profile is generated for each

dim level. The CS1630/31 provides two-dimensional mapping

for the color LED’s current only, and one-dimensional

mapping (current versus dim level) for the other string. A

simplified block diagram of the color control system is shown

in Figure 11.

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