Datasheet

10701fe
3
LT1070/LT1071
ELECTRICAL CHARACTERISTICS
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
FB
Flyback Reference Voltage I
FB
= 50µA 15 16.3 17.6 V
● 14 18.0 V
Change in Flyback Reference Voltage 0.05 ≤ I
FB
≤ 1mA 4.5 6.8 8.5 V
Flyback Reference Voltage Line Regulation I
FB
= 50µA, 3V ≤ V
IN
≤ V
MAX
(Note 3) 0.01 0.03 %/V
Flyback Amplifier Transconductance (g
m
) ∆I
C
= ±10µA 150 300 650 µmho
Flyback Amplifier Source and Sink Current V
C
= 0.6V, I
FB
= 50µA (Source) ● 15 32 70 µA
V
C
= 0.6V, I
FB
= 50µA (Sink) ● 25 40 70 µA
B
V
Output Switch Breakdown Voltage 3V ≤ V
IN
≤ V
MAX
, I
SW
= 1.5mA
(LT1070/LT1071)
● 65 90 V
(LT1070HV/LT1071HV)
● 75 90 V
V
SAT
Output Switch “On” Resistance (Note 4) LT1070 ● 0.15 0.24 Ω
LT1071
● 0.30 0.50 Ω
Control Voltage to Switch Current LT1070 8 A/V
Transconductance LT1071 4 A/V
I
LIM
Switch Current Limit (LT1070) Duty Cycle ≤ 50%, T
J
≥ 25°C ● 510A
Duty Cycle ≤ 50%, T
J
< 25°C ● 511A
Duty Cycle = 80% (Note 5)
● 410A
Switch Current Limit (LT1071) Duty Cycle ≤ 50%, T
J
≥ 25°C ● 2.5 5.0 A
Duty Cycle ≤ 50%, T
J
< 25°C ● 2.5 5.5 A
Duty Cycle = 80% (Note 5)
● 2.0 5.0 A
∆I
IN
Supply Current Increase During 25 35 mA/A
∆I
SW
Switch “On” Time
f Switching Frequency 35 40 45 kHz
● 33 47 kHz
DC (Max) Maximum Switch Duty Cycle 90 92 97 %
Flyback Sense Delay Time 1.5 µs
Shutdown Mode Supply Current 3V ≤ V
IN
≤ V
MAX
, V
C
= 0.05V 100 250 µA
Shutdown Mode Threshold Voltage 3V ≤ V
IN
≤ V
MAX
100 150 250 mV
● 50 300 mV
Note 1: Absolute Maximum Ratings are those values beyond which the life of
a device may be impaired.
Note 2: Minimum switch “on” time for the LT1070/LT1071 in current limit is
≈1µs. This limits the maximum input voltage during short-circuit conditions,
in the buck and inverting modes only , to ≈35V. Normal (unshorted) conditions
are not affected. Mask changes are being implemented which will reduce
minimum “on” time to ≤1µs, increasing maximum short-circuit input voltage
above 40V. If the present LT1070/LT1071 (contact factory for package date
code) is being operated in the buck or inverting mode at high input voltages
and short-circuit conditions are expected, a resistor must be placed in series
with the inductor, as follows:
The value of the resistor is given by:
R = – R
L
t • f • V
IN
– V
F
I
LIMIT
t = Minimum “on” time of LT1070/LT1071 in current limit, ≈1µs
f = Operating frequency (40kHz)
V
F
= Forward voltage of external catch diode at I
LIMIT
I
LIMIT
= Current limit of LT1070 (≈8A), LT1071 (≈4A)
R
L
= Internal series resistance of inductor
Note 3: V
MAX
= 55V for LT1070HV and LT1071HV to avoid switch
breakdown.
Note 4: Measured with V
C
in hi clamp, V
FB
= 0.8V. I
SW
= 4A for LT1070
and 2A for LT1071.
Note 5: For duty cycles (DC) between 50% and 80%, minimum
guaranteed switch current is given by I
LIM
= 3.33 (2 – DC) for the
LT1070 and I
LIM
= 1.67 (2 – DC) for the LT1071.
The ● denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at T
A
= 25°C. V
IN
= 15V, V
C
= 0.5V, V
FB
= V
REF
, output pin open unless otherwise specified.