3
LT1956/LT1956-5
1956f
PARAMETER CONDITIONS MIN TYP MAX UNITS
Switch Current Limit V
C
Open, Boost = V
IN
+ 5V, FB = 1V or V
SENSE
= 4.1V ● 1.5 2 3 A
Switch On Resistance I
SW
= 1.5A, Boost = V
IN
+ 5V (Note 7) 0.2 0.3 Ω
● 0.4 Ω
Maximum Switch Duty Cycle FB = 1V or V
SENSE
= 4.1V 82 90 %
● 75 90 %
Switch Frequency V
C
Set to Give DC = 50% 460 500 540 kHz
● 430 570 kHz
f
SW
Line Regulation 5.5V ≤ V
IN
≤ 60V ● 0.05 0.15 %/V
f
SW
Shifting Threshold Df = 10kHz 0.8 V
Minimum Input Voltage (Note 3) ● 4.6 5.5 V
Minimum Boost Voltage (Note 4) I
SW
≤ 1.5A ● 23 V
Boost Current (Note 5) Boost = V
IN
+ 5V, I
SW
= 0.5A ● 12 25 mA
Boost = V
IN
+ 5V, I
SW
= 1.5A ● 42 70 mA
Input Supply Current (I
VIN
) (Note 6) V
BIAS
= 5V 1.4 2.2 mA
Output Supply Current (I
BIAS
) (Note 6) V
BIAS
= 5V 2.9 4.2 mA
Shutdown Supply Current SHDN = 0V, V
IN
≤ 60V, SW = 0V, V
C
Open 25 75 µA
● 200 µA
Lockout Threshold V
C
Open ● 2.30 2.42 2.53 V
Shutdown Thresholds V
C
Open, Shutting Down ● 0.15 0.37 0.6 V
V
C
Open, Starting Up ● 0.25 0.45 0.6 V
Minimum SYNC Amplitude ● 1.5 2.2 V
SYNC Frequency Range 580 700 kHz
SYNC Input Resistance 20 kΩ
The ● denotes specifications which apply over the full operating temperature range, otherwise specifications are at T
J
= 25°C.
V
IN
= 15V, V
C
= 1.5V, SHDN = 1V, Boost o/c, SW o/c, unless otherwise noted.
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: Gain is measured with a V
C
swing equal to 200mV above the low
clamp level to 200mV below the upper clamp level.
Note 3: Minimum input voltage is not measured directly, but is guaranteed
by other tests. It is defined as the voltage where internal bias lines are still
regulated so that the reference voltage and oscillator remain constant.
Actual minimum input voltage to maintain a regulated output will depend
upon output voltage and load current. See Applications Information.
Note 4: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the internal power switch.
Note 5: Boost current is the current flowing into the BOOST pin with the
pin held 5V above input voltage. It flows only during switch on time.
Note 6: Input supply current is the quiescent current drawn by the input
pin when the BIAS pin is held at 5V with switching disabled. Bias supply
current is the current drawn by the BIAS pin when the BIAS pin is held at
5V. Total input referred supply current is calculated by summing input
supply current (I
VIN
) with a fraction of supply current (I
BIAS
):
I
TOTAL
= I
VIN
+ (I
BIAS
)(V
OUT
/V
IN
)
with V
IN
= 15V, V
OUT
= 5V, I
VIN
= 1.4mA, I
BIAS
= 2.9mA, I
TOTAL
= 2.4mA.
Note 7: Switch on resistance is calculated by dividing V
IN
to SW voltage by
the forced current (1.5A). See Typical Performance Characteristics for the
graph of switch voltage at other currents.
Note 8: The LT1956EFE/LT1956EFE-5/LT1956EGN/LT1956EGN-5 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 LT1956IFE/LT1956IFE-5/
LT1956IGN/LT1956IGN-5 are guaranteed over the full –40°C to 125°C
operating junction temperature range.
Note 9: Transconductance and voltage gain refer to the internal amplifier
exclusive of the voltage divider. To calculate gain and transconductance,
refer to the SENSE pin on fixed voltage parts. Divide values shown by the
ratio V
OUT
/1.219.
Note 10: This IC includes overtemperature protection that is intended to
protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation above the specified maximum operating junction
temperature may impair device reliability.
