Cirrus Logic CS1616A - Manual (Page 2)

CS1615A/16A
2 DS1033PP2
1. INTRODUCTION
Figure 1. CS1615A/16A Block Diagram
A typical schematic using the CS1615A/16A IC is shown on the
previous 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 V
DD
power is always available
to the IC. During normal operation, an auxiliary winding on the
flyback transformer or buck-boost inductor back-biases the
source-follower circuit and provides steady-state operating
current to the IC to improve system efficiency.
Rectified input voltage V
rect
is sensed as a current into pin IAC
and is used to control the adaptive dimmer-compatibility
algorithm and to extract the phase of the input voltage for output
dimming control. The SOURCE pin is used to provide a control
signal for the high-voltage source-follower circuit during Leading-
edge Mode and Trailing-edge Mode; it also provides the current
during startup.
The digital dual-mode controller is implemented with
peak-current mode primary-side regulation, which eliminates the
need for additional components to provide feedback from the
secondary and reduces system cost and complexity. Voltage
across a user-selected resistor is sensed through pin FBSENSE
to control the peak current of the primary-side inductor. Leading-
edge and trailing-edge blanking on pin FBSENSE prevents false
triggering. The required target LED current and average flyback
transformer and buck-boost inductor input current are set by
attaching resistors R
CTRL1
and R
CTRL2
on pins CTRL1 and
CTRL2, respectively. The controller ensures half line-cycle
averaged constant output current.
Pin FBAUX is used for zero-current detection to ensure
quasi-resonant switching of the single stage output. When an
external negative temperature coefficient (NTC) thermistor is
connected to pin eOTP, the CS1615A/16A monitors the system
temperature, allowing the controller to reduce the output current
of the system. If the temperature reaches a designated high set
point, the IC is shut down and stops switching.
2
IAC
SOURCE
5
SGND
15k
ADC
I
ref
11
FBSENSE
+
-
DAC
+
-
Peak
Control
12
GND
OLP
+
-
OCP
Blank
3 CLAMP
V
OCP (th)
V
OLP (th )
V
P k_Max (th )
I CLA MP
+
- V
S OURCE(th)
MUX
9
+
-
I
CONNE CT
V
CONNE CT(th)
10
CTRL2
8
CTRL1
eOTP
FBAUX
16 +
-
Zero-current
Detect
+
-
Output
Overvoltage
V ZCD(th)
V OV P(th )
t
VAUX
14 VDD
+
-
V DD(on)
V
DD(off )
Voltage
Regulator
V
Z
POR
13 GD
VDD
VDD
VDD
4
+
-
V
FS TA RT(th )
3