LT1186 Linear Technology, LT1186 Datasheet - Page 8

• Manufacturer Part Number: LT1186
• Description: DAC Programmable CCFL Switching Regulator(Bits-to-NitsTM)
• Manufacturer: Linear Technology

PIN
LT1186F
AGND (Pin 5): This is the low current analog ground. It is
the negative sense terminal for the internal 1.24V refer-
ence and the I
Connect low current signal paths that terminate to ground
and frequency compensation components that terminate
to ground directly to this pin for best regulation and
performance.
SHDN (Pin 6): Pulling this pin low causes complete
regulator shutdown with quiescent current typically re-
duced to 35 A. If the pin is not used, use a pull-up resistor
to force a logic high level (maximum of 6V) or tie directly
to V
output current setting and returns to this level when the
logic-low signal at the shutdown pin is removed.
CLK (Pin 7): This pin is the shift clock for the DAC. This
clock synchronizes the serial data and is a Schmitt
trigger input. In standard SPI mode, the clock shifts data
into D
of the clock respectively. In pulse mode, the rising edge
of the clock either increments or decrements the counter.
This action depends on the choice of a 1-wire interface
(increment only) or a 2-wire interface (increment/decre-
ment).
CS (Pin 8): This pin is the chip select input for the DAC. In
SPI mode, a logic low on the CS pin enables the DAC to
receive and transfer 8-bit serial data. After the serial input
data is shifted in, a rising edge of CS transfers the data into
the counter, the DAC assumes the new I
D
up, a logic high places the DAC into pulse mode. Pulling CS
low after this places the DAC into SPI mode until V
resets.
D
DAC. In SPI mode, the 8-bit serial data is shifted into the
D
mode, on power up, a logic high at D
function from D
ment-only mode and the pin function shifts to up or down
increment control of DAC output current. If UP/DN re-
ceives a logic-low signal, the counter configures to incre-
ment/decrement mode until V
8
OUT
IN
IN
U
input on each rising edge of the clock signal. In pulse
or UP/DN (Pin 9): This pin is the digital input for the
CC
pin returns to the high impedance state. On power
IN
. In a shutdown condition, the DAC retains its last
FUNCTIONS
and out of D
U
CCFL
IN
to UP/DN, puts the counter into incre-
summing voltage in the LT1186F.
U
OUT
on the rising and falling edges
CC
resets.
IN
OUT
transfers the pin
value and the
CC
D
SPI mode, D
D
every falling edge of the clock. When CS rises high again,
D
D
I
DAC and provides an output current of 50 3 A over
temperature. This pin can be biased from – 20V to 2V for
a 3.3V V
V
and provides the programming current which sets operat-
ing lamp current. The I
change when it is tied to the I
The programming current is sourced from the I
sunk by the I
V
IC accepts an input voltage range of 3V minimum to 6.5V
maximum with little change in quiescent current (zero
switch current). An internal, low-dropout regulator pro-
vides a 2.4V supply for most of the internal circuitry.
Supply current increases as switch current increases at a
rate approximately 1/50 of switch current. This corre-
sponds to a forced Beta of 50 for the power switch. The IC
incorporates undervoltage lockout by sensing regulator
dropout and locking out switching for input voltages
below 2.5V. Hysteresis is not used to maximize the useful
range of input voltage. The typical input voltage is a 3.3V
or 5V logic supply.
ROYER (Pin 13): This pin connects to the center-tapped
primary of the Royer converter and is used with the BAT
pin in a floating-lamp configuration where lamp current is
controlled by sensing Royer primary-side converter cur-
rent. This pin is the inverting terminal of a high-side
current sense amplifier. The typical quiescent current is
50 A into the pin. If the CCFL regulator is not used in a
floating-lamp configuration, tie the Royer and BAT pins
together.
OUT
OUT
OUT
OUT
OUT
CC
CC
supply voltage. However, this pin is tied to the I
(Pin 12): This is the supply pin for the LT1186F. The
(Pin 11): This pin is the analog current output for the
(Pin 10): This pin is the digital output for the DAC. In
pin then serially transfers the previous 8-bit data on
is always three-stated.
returns to a three-state condition. In pulse mode,
CC
supply voltage or from – 20V to 2.5V for a 5V
CCFL
OUT
is in three-state until CS falls low. The
pin.
OUT
pin has very little bias voltage
CCFL
pin as I
CCFL
is regulated.
OUT
CCFL
pin and
pin