LT1768
3
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
PWM
PWM Input Bias Current ● 0.6 4 µA
PWM Duty Cycle V
PROG
= 1.75 45 50 55 %
PWM Frequency C
T
= 0.22µF (Note 7) 90 110 130 Hz
V
DIO1/2
DIO1/2 Positive Voltage I
DIO
= 14mA 1.7 1.9 V
DIO1/2 Negative Voltage I
DIO
= –14mA –1.1 –1.3 V
V
VCCLAMP
VC High Clamp Voltage V
PROG
= 4.5V (Note 8) 3.6 3.7 3.9 V
VC Switching Threshold V
PROG
= 4.5V (Note 8) 0.5 0.7 0.95 V
I
SENSE
SENSE Input Bias Current V
SENSE
= 0V –25 –30 µA
V
SENSE
SENSE Threshold for Current Limit V
VC
= V
VCCLAMP
, Duty Cycle <50%, V
PROG
= 1V 85 100 115 mV
V
VC
= V
VCCLAMP
, Duty Cycle 80%, V
PROG
= 1V 90 mV
I
DIO1/2
to I
RMAX
Ratio V
PROG
= 4.5V (Note 5) ● 94 98 104 A/A
V
PROG
= 4.5V, I
DIO1
or I
DIO2
= 0, V
VC
= 2.5V,
(Note 5) 45 49 55 A/A
I
DIO1/2
to I
RMIN
Ratio V
PROG
< 0.75V (Note 6) ● 9 10 11 A/A
V
PROG
< 0.75V, I
DIO1
or I
DIO2
= 0, V
VC
= 2.5V,
(Note 6) 9 10 11 A/A
I
GATE
GATE Drive Peak Source Current 1.5 A
GATE Drive Peak Sink Current 1.5 A
GATE Drive Saturation Voltage V
VIN
= 12V, I
GATE
= –100mA, V
PROG
= 4.5V ● 9.8 10.2 V
GATE Drive Clamp Voltage V
VIN
= 24V, I
GATE
= –10mA, V
PROG
= 4.5V ● 12.5 14 V
GATE Drive Low Saturation Voltage I
GATE
= 100mA ● 0.4 0.6 V
Open LAMP Threshold (Note 9) 100 125 150 µA
FAULT Pin Saturation Voltage I
FAULT
= 1mA, I
DI01
, I
DI02
= 0µA, V
PROG
= 4.5V 0.2 0.3 V
FAULT Pin Leakage Current V
FAULT
= 5V 20 100 nA
Thermal ShutdownTemperature 160 °C
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: This is the threshold voltage where the lamp current switches
from zero current to minimum lamp current. For V
PROG
less than the
threshold voltage, lamp current will be at zero. For V
PROG
greater than the
threshold voltage, lamp current will be equal to the minimum lamp
current. Minimum lamp current is set by the value of the resistor from the
R
MIN
pin to ground. See Applications Information for more details.
Note 3: This is the threshold voltage where the device starts to pulse width
modulate the lamp current. For V
PROG
less than the threshold voltage,
lamp current will be equal to the minimum lamp current. For V
PROG
greater than the threshold voltage, lamp current will be pulse width
modulated between the minimum lamp current and some higher value.
Minimum lamp current is set by the value of the resistor from the R
MIN
pin
to ground. The higher value lamp current is a function of the R
MAX
resistor
to ground value, and the voltages on the PWM and PROG pins. See
Applications Information for more details.
Note 4: This is the threshold voltage where the lamp current reaches its
maximum value. For V
PROG
greater than the threshold voltage, there will
be no increase in lamp current. For V
PROG
less than the threshold voltage,
lamp current will be at some lower value. Maximum lamp current is set by
The ● denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
VIN
= 12V, I
DIO1/2
= 250µA, V
PROG
= 0V, V
PWM
= 2.5V, I
RMAX
= –100µA,
I
RMIN
= –100µA, unless otherwise specified.
the value of the resistor from the R
MAX
pin to ground. The lower value
lamp current is a function of the R
MIN
and R
MAX
resistors, and the
voltages on the PWM and PROG pins. See Applications Information for
more details.
Note 5: I
DIO1/2
to I
RMAX
ratio is determined by setting I
RMAX
to –100µA,
V
PROG
to 4.5V, V
VC
to 2.5V, and then ramping a DC current out of the
DIO1/2 pins from zero until the DC current in the VC voltage source
current equals zero. The I
DIO1/2
to I
RMAX
ratio is then defined as (I
DIO1
+
I
DIO2
)/I
RMAX
. See Applications Information for more details.
Note 6: I
DIO1/2
to I
RMIN
ratio is determined by setting I
RMIN
to –100µA,
V
PROG
to 0.75V, V
VC
to 2.5V, and then ramping a DC current out of the
DIO1/2 pins from zero until the DC current in the VC voltage source
current equals zero. The I
DIO1/2
to I
RMIN
ratio is then defined as (I
DIO1
+
I
DIO2
)/I
RMIN
. See Applications Information for more details.
Note 7: The PWM frequency is set by the equation PWMFREQ = 22Hz/
C
T
(µF).
Note 8: For VC voltages less than the switching threshold, GATE switching
is disabled.
Note 9: An open lamp will be detected if either I
DIO1
or I
DIO2
is less than
the threshold current for at least 1 full PWM cycle.
