Datasheet LT1977 (Analog Devices) - 3

LT1977
ELECTRICAL CHARACTERISTICS The
●
denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TJ = 25
°
C. VIN = 12V, SHDN = 12V, BIAS = 5V, FB/PGFB = 1.25V, CSS/SYNC = 0V unless otherwise noted. SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Switch On Resistance (Note 9) ● 0.2 0.4 Ω Switching Frequency ● 425 500 575 kHz Maximum Duty Cycle 86 92 % Minimum SYNC Amplitude 1.5 2.0 V SYNC Frequency Range 575 700 kHz SYNC Input Impedance 85 kΩ ICSS CSS Current Threshold (Note 10) FB = 0V 7 13 20 µA IPGFB PGFB Input Current 25 100 nA VPGFB PGFB Voltage Threshold (Note 11) ● 88 90 92 % ICT CT Source Current (Note 11) 2 3.6 5.5 µA CT Sink Current (Note 11) 1 2 mA VCT CT Voltage Threshold (Note 11) 1.16 1.2 1.26 V PG Leakage (Note 11) VPG = 12V 0.1 1 µA PG Sink Current (Note 11) PGFB = 1V, PG = 400mV 100 200 µA
Note 1:
Absolute Maximum Ratings are those values beyond which the life
Note 5:
Minimum BIAS voltage is the voltage on the BIAS pin when IBIAS is of a device may be impaired. sourced into the pin.
Note 2:
The LT1977EFE is guaranteed to meet performance specifications
Note 6:
This is the minimum voltage across the boost capacitor needed to from 0°C to 125°C junction temperature. Specifications over the –40°C to guarantee full saturation of the internal power switch. 125°C operating junction temperature range are assured by design,
Note 7:
Boost current is the current flowing into the BOOST pin with the pin characterization and correlation with statistical process controls. The held 3.3V above input voltage. It flows only during switch on time. LT1977IFE is guaranteed and tested over the full –40°C to 125°C
Note 8:
Gain is measured with a VC swing from 1.15V to 750mV. operating junction temperature range.
Note 9:
Switch on resistance is calculated by dividing VIN to SW voltage by the
Note 3:
Minimum input voltage is defined as the voltage where switching forced current (1.5A). See Typical Performance Characteristics for the graph starts. Actual minimum input voltage to maintain a regulated output will of switch voltage at other currents. depend upon output voltage and load current. See Applications
Note 10:
The C Information. SS threshold is defined as the value of current sourced into the CSS pin which results in an increase in sink current from the VC pin. See the
Note 4:
Supply input current is the quiescent current drawn by the input Soft-Start section in Applications Information. pin. Its typical value depends on the voltage on the BIAS pin and operating
Note 11:
The PGFB threshold is defined as the percentage of V state of the LT1977. With the BIAS pin at 0V, all of the quiescent current REF voltage which causes the current source output of the C required to operate the LT1977 will be provided by the V T pin to change from IN pin. With the sinking (below threshold) to sourcing current (above threshold). When BIAS voltage above its minimum input voltage, a portion of the total sourcing current, the voltage on the C quiescent current will be supplied by the BIAS pin. Supply sleep current is T pin rises until it is clamped internally. When the clamp is activated, the output of the PG pin will be set defined as the quiescent current during the “sleep” portion of Burst Mode to a high impedance state. When the C operation. See Applications Information for determining application supply T clamp is inactive the PG pin will be set active low with a current sink capability of 200µA. currents. 1977fa 3