CS1630 Datasheet, PDF (4/56 Pages) Cirrus Logic – 2-Channel TRIAC Dimmable LED Driver IC

CS1630/31
1. INTRODUCTION
BSTOUT ¹⁶
IAC ²
15 k
Iref
MUX
ADC
15k
BSTAUX ¹
SOURCE ⁵
VFB ZCD(th)
+
-
+
V S OURCE(th ) -
Boost ZCD
t B S TZCD
I S OURCE
SGND ⁴
SDA ⁶
SCL ⁷
SYNC ⁹
NC ⁸
eOTP ¹⁰
VDD
ICONNE CT
-
V CONNE CT(th) ₊
Voltage
Regulator
POR
+
-
V S T(th )
VS TP(th )
VZ
Blank
3
OLP
OCP
Peak
Control
DAC
-
+ VOLP (th)
+
- VOCP (th )
+
-
V P k_Max(th)
Output Open
tFB ZCD
Flyback ZCD
+
- VOV P (th )
+
- V_{FB ZCD(th)}
VDD
I_{CLA MP}
14 _VDD
13 _GD
12 _GND
11 _FBSENSE
15 _FBAUX
3 _CLAMP
Figure 1. CS1630/31 Block Diagram
A typical schematic using the CS1630/31 IC is shown on the
front page.
Startup current is provided from a patent-pending, external
high-voltage source-follower network. In addition to providing
startup current, this unique topology is integral in providing
compatibility with digital dimmers by ensuring VDD power is
always available to the IC. During steady-state operation, an
auxiliary winding on the boost inductor back-biases the
source-follower circuit and provides steady-state operating
current to the IC to improve system efficiency.
The rectified input voltage is sensed as a current into pin IAC
and is used to control the adaptive dimmer compatibility
algorithm and extract the phase of the input voltage for output
dimming control. During steady-state operation, the external
high-voltage, source-follower circuit is source-switched in
critical conduction mode (CRM) to boost the input voltage.
This allows the boost stage to maintain good power factor,
provide dimmer compatibility, reduce bulk capacitor ripple
current, and provide a regulated input voltage to the second
stage.
The current into the boost output voltage sense pin (BSTOUT)
senses the output voltage of the CRM boost front-end.
The quasi-resonant second stage is implemented with peak-
current mode primary-side control, which eliminates the need
for additional components to provide feedback from the
secondary and reduces system cost and complexity.
Voltage across an external user-selected resistor is sensed
through pin FBSENSE to control the peak current through the
second stage inductor. Leading-edge and trailing-edge
blanking on pin FBSENSE prevents false triggering.
Pin FBAUX is used to sense the second stage inductor
demagnetization to ensure quasi-resonant switching of the
output stage.
An internal current source is adjusted by a feedback loop to
regulate a constant reference voltage on pin eOTP for external
negative temperature coefficient (NTC) thermistor
measurements. An external NTC is connected to pin eOTP to
provide thermal protection of the system and LED temperature
compensation. The output current of the system is steadily
reduced when the system temperature exceeds a
programmable temperature set point. If the temperature
reaches a designated high set point, the IC is shutdown and
stops switching.
4
DS954F2