LT1976/LT1976B
4
1976bfg
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LT1976EFE/LT1976BEFE are guaranteed to meet performance
specifications from 0°C to 125°C junction temperature. Specifications over
the –40°C to 125°C operating junction temperature range are assured by
design, characterization and correlation with statistical process controls.
The LT1976IFE/LT1976BIFE/LT1976HFE are guaranteed and tested over
the full –40°C to 125°C operating junction temperature range. The
LT1976HFE is also tested to the LT1976HFE electrical characteristics table
at 140°C operating junction temperature. High junction temperatures
degrade operating lifetimes.
Note 3: Minimum input voltage is defined as the voltage where switching
starts. Actual minimum input voltage to maintain a regulated output will
depend upon output voltage and load current. See Applications
Information.
Note 4: Supply input current is the quiescent current drawn by the input
pin. Its typical value depends on the voltage on the BIAS pin and operating
state of the LT1976. With the BIAS pin at 0V, all of the quiescent current
required to operate the LT1976 will be provided by the V
IN
pin. With the
BIAS voltage above its minimum input voltage, a portion of the total
quiescent current will be supplied by the BIAS pin. Supply sleep current
for the LT1976 is defined as the quiescent current during the “sleep”
portion of Burst Mode operation. See Applications Information for
determining application supply currents.
Note 5: Minimum BIAS voltage is the voltage on the BIAS pin when I
BIAS
is
sourced into the pin.
Note 6: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the internal power switch.
Note 7: Boost current is the current flowing into the BOOST pin with the
pin held 3.3V above input voltage. It flows only during switch on time.
Note 8: Gain is measured with a V
C
swing from 1.15V to 750mV.
Note 9: Switch on resistance is calculated by dividing V
IN
to SW voltage by
the forced current (1.5A LT1976, 1.2A LT1976B). See Typical Performance
Characteristics for the graph of switch voltage at other currents.
Note 10: The C
SS
threshold is defined as the value of current sourced into
the C
SS
pin which results in an increase in sink current from the V
C
pin.
See the Soft-Start section in Applications Information.
Note 11: The PGFB threshold is defined as the percentage of V
REF
voltage
which causes the current source output of the C
T
pin to change from
sinking (below threshold) to sourcing current (above threshold). When
sourcing current, the voltage on the C
T
pin rises until it is clamped
internally. When the clamp is activated, the output of the PG pin will be set
to a high impedance state. When the C
T
clamp is inactive the PG pin will
be set active low with a current sink capability of 200μA.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
I
PK
SW Current Limit 2.4 A
Switch On Resistance (Note 9) ● 0.2 0.6 Ω
Switching Frequency BOOST = OPEN ● 150 200 260 kHz
Maximum Duty Cycle 90 92 %
Minimum SYNC Amplitude 1.5 2.0 V
SYNC Frequency Range 230 600 kHz
SYNC Input Impedance SYNC = 0.5V 85 kΩ
I
CSS
C
SS
Current Threshold (Note 10) 7 13 20 μA
I
PGFB
PGFB Input Current 25 100 nA
V
PGFB
PGFB Voltage Threshold (Note 11) ● 87 90 93 %
I
CT
C
T
Source Current (Note 11) ● 1.5 3.6 5.5 μA
C
T
Sink Current (Note 11) 1 2 mA
V
CT
C
T
Voltage Threshold (Note 11) 1.16 1.2 1.26 V
PG Leakage (Note 11) PG = 12V 0.1 1 μA
PG Sink Current (Note 11) PGFB = 1V, PG = 400mV 120 200 μA
ELECTRICAL CHARACTERISTICS
The ● denotes the specifications which apply over the full –40°C to 140°C
operating temperature range, otherwise specifications are at T
J
= 25°C. V
IN
= 12V, SHDN = 12V, BOOST = 15.3V, BIAS = 5V,
FB/PGFB = 1.25V, C
SS
/SYNC = 0V unless otherwise noted.
