CS1630 Datasheet, PDF (12/56 Pages) Cirrus Logic – 2-Channel TRIAC Dimmable LED Driver IC

CS1630/31
5. GENERAL DESCRIPTION
5.1 Overview
The CS1630 and CS1631 are high-performance offline AC/DC
LED drivers for dimmable and high color rendering index (CRI)
LED replacement lamps and luminaires. They feature Cirrus
Logic’s proprietary digital dimmer compatibility control
technology and digital correlated color temperature (CCT) control
system that enables two-channel LED color mixing. The CS1630
is designed for 120VAC line voltage applications, and the
CS1631 is optimized for 230VAC line voltage applications.
The CS1630/31 integrates a critical conduction mode (CRM)
boost converter, providing power factor correction and superior
dimmer compatibility with a primary-side regulated quasi-
resonant second stage, which is configurable for isolated and
non-isolated topologies. The digital CCT control system provides
the ability to program dimming profiles, such as constant CCT
dimming and black body line dimming. The CS1630/31
optimizes LED color mixing by temperature compensating LED
current with an external negative temperature coefficient
(NTC) thermistor. The IC controller is also equipped with power
line calibration for remote system calibration and end-of-line
programming. The CS1630/31 provides a register lockout
feature for security against potential access to proprietary
registers.
5.2 Startup Circuit
An external, high-voltage source-follower circuit is used to
deliver startup current to the IC. During steady-state operation,
an auxiliary winding on the boost inductor biases this circuit to
an off state to improve system efficiency, and all IC supply
current is generated from the auxiliary winding. The patent
pending technology of the external, high-voltage source-
follower circuit enables system compatibility with digital
dimmers (dimmers containing an internal power supply) by
providing a continuous path for a dimmer’s power supply to
recharge during its off state. During steady-state operation,
high-voltage FET Q1 is source-switched by a variable internal
current source on the SOURCE pin to create the boost circuit.
A Schottky diode with a forward voltage less than 0.6V is
recommended for D5. Schottky diode D5 will limit inrush current
through the internal diode, preventing damage to the IC.
5.3 Dimmer Switch Detection
The CS1630/31 dimmer switch detection algorithm determines
if the solid-state lighting system is controlled by a regular switch,
a leading-edge dimmer, or a trailing-edge dimmer. Dimmer
switch detection is implemented using two modes: Dimmer
Learn Mode and Dimmer Validate Mode. These assist in
limiting the system power losses. Once the IC reaches UVLO
start threshold V_ST(th) and begins operating, the CS1630/31 is
in Dimmer Learn Mode, allowing the dimmer switch detection
circuit to set the operating state of the IC to one of three modes:
No-dimmer Mode, Leading-edge Mode, or Trailing-edge Mode.
5.3.1 Dimmer Learn Mode
In Dimmer Learn Mode, the dimmer detection circuit spends
approximately two line-cycles learning whether there is a
dimmer switch and, if present, whether it is a trailing-edge or
leading-edge dimmer. A modified version of the leading-edge
algorithm is used. The trailing-side slope of the input line
voltage is sensed to decide whether the dimmer switch is a
trailing-edge dimmer. The dimmer detection circuit transitions to
Dimmer Validate Mode once the circuit detects that a dimmer is
present.
5.3.2 Dimmer Validate Mode
During normal operation, CS1630/31 is in Dimmer Validate
Mode. This instructs the dimmer detection circuit to periodically
validate that the IC is executing the correct algorithm for the
attached dimmer. The dimmer detection algorithm periodically
verifies the IC operating state as a protection against incorrect
detection. As additional protection, the output of the dimmer
detection algorithm is low-pass filtered to prevent noise or
transient events from changing the IC’s operating mode. The IC
will return to Dimmer Learn Mode when it has determined that
the wrong algorithm is being executed.
5.3.3 No-dimmer Mode
Upon detection that the line is not phase cut with a dimmer, the
CS1630/31 operates in No-dimmer Mode, where it provides a
power factor that is in excess of 0.9. The CS1630/31
accomplishes this by boosting in CRM and DCM mode. The
peak current is modulated to provide link regulation. The
CS1630/31 alternates between two settings of peak current. To
regulate the boost output voltage, the CS1630/31 uses a peak
current set by register PEAK_CUR (see "Peak Current
(PEAK_CUR) – Address 51" on page 39). The time that this
current is used is determined by an internal compensation loop
to regulate the boost output voltage. The internal algorithm will
reduce the peak current of the boost stage to maintain output
voltage regulation and obtain the desired power factor.
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