Specifications
Rev. 1.0 January 2012
www.aosmd.com
Page 5 of 5
AOZ197
8
Pin 12: FB2
This is the feedback input for boost controller for CH2.
This pin should connect to a resistor that senses the
LED current. The FB2 voltage will be regulated to Pin
10 (ISET) voltage. If the voltage at FB2 pin exceeds
1V due to a fault condition CH2 will shut down for
40ms and will try again every 40ms until the fault
condition is removed. Note that this is the only fault
condition that will not assert a FLAG.
Pin 13: CS2
This is the input for peak current sense for CH2. This
pin serves the functions of current feedback, peak
current limit detection and fault current detection. The
pin current limit is internally set to 0.4V for peak
current limit and 0.48V for fault current detection,
under fault current detection, CH2 controller will assert
FLAG, shutdown and reset every 40ms.
Pin 14: DBRT2
This is the input for digital brightness control for CH2.
A PWM logic signal is applied to this pin to vary the
brightness of the LED. The brightness of the LED is
proportional to the duty cycle of the PWM logic signal.
The input signal will control the output driver at
DPWM2 pin. This input pin cannot be left floating.
Pin 15: OVP2
This is the input for LED Over-Voltage Protection.
OVP2 monitors Channel 2 LED output voltage through
a resistor divider. When the voltage at this pin is
higher than 1V, Channel 2 will immediately stop
switching for 40ms and Pin 20 (FLAG) is instantly
asserted HIGH, indicating a Fault condition, CH2
controller will reset and restart again after 40ms. If
fault condition persists it will repeat until fault condition
is removed.
Pin 16: COMP2
This is for feedback loop compensation for Channel 2.
It is the output of the transconductance error amplifier
that controls PWM logic for the boost controller. An
RC network should be connected from COMP2 to
GND to generate the compensation for boost 2
feedback loop.
Pin 18: GATE2
This is the driver output for the gate of boost NMOS
switch for Channel 2. The GATE = HIGH voltage is
equal to VIN voltage. It is recommended to add a 1Ω
resistor between this pin and the NMOS gate. The
resistor value can be optimized depending on the
selection of NMOS switch. To reduce system noise
and input ripple current, GATE2 is 180⁰ out phase
from GATE1.
PIN 19: DPWM2
This is the driver outputs for the gate of the LED
current control NMOS switch for channel 2. DPWM2 =
LOW if Pin 14 DBRT2 signal is low or fault condition is
triggered. The DPWM2 = HIGH if DBRT2 is high
under normal operating conditions. The high gate
voltage at DPWM2 equals Pin1 VIN voltage. It is
recommended to add 1Ω resistor between this pin and
NMOS gate. The resistor value can be optimized
depending on the LED current and selection of
NMOS. DPWM2 can be driven simultaneously with
DPWM1 or independently from DPWM1.
PIN 20: FLAG
This is an open drain output that is asserted HIGH any
time a fault condition is detected on either or both
CH1 or CH2. Whenever FLAG is asserted high the
controller shuts down and resets every 40ms until
fault condition is removed. FLAG is also asserted at
start-up, if Pin1 VIN voltage is present before boost
input voltage is applied, FLAG will clear when input
boost voltage becomes present and SCP Pin 11
reaches 1.14V. To avoid a FLAG at power-up, follow
proper power up sequence, Pin 1 VIN voltage should
be applied after boost input voltage PVIN has reached
operating level. The Only Fault condition when FLAG
will not be asserted but controller will still shutdown
and reset every 40ms is when either or both FB1 or
FB2 exceed 1V due to system noise or Shorted LED
string.