Datasheet

3
LT1767/LT1767-1.8/
LT1767-2.5/LT1767-3.3/LT1767-5
sn1767 1767fas
ELECTRICAL CHARACTERISTICS
FB Input Resistance LT1767-1.8 ● 10.5 15 21 kΩ
LT1767-2.5
● 14.7 21 30 kΩ
LT1767-3.3 ● 19 27.5 39 kΩ
LT1767-5
● 29 42 60 kΩ
Error Amp Voltage Gain 0.4V < V
C
< 0.9V 150 350
Error Amp Transconductance ∆I
VC
= ±10µA ● 500 850 1300 µMho
V
C
Pin Source Current V
FB
= V
NOM
– 17% ● 80 120 160 µA
V
C
Pin Sink Current V
FB
= V
NOM
+ 17% ● 70 110 180 µA
V
C
Pin to Switch Current Transconductance 2.5 A/V
V
C
Pin Minimum Switching Threshold Duty Cycle = 0% 0.35 V
V
C
Pin 1.5A I
SW
Threshold 0.9 V
Maximum Switch Duty Cycle V
C
= 1.2V, I
SW
= 400mA 85 90 %
● 80 %
Minimum Boost Voltage Above Switch I
SW
= –1.5A, 0°C ≤ T
A
≤ 125°C and –1.3A, T
A
< 0°C ● 1.8 2.7 V
Boost Current I
SW
= –0.5A (Note 4) ● 10 15 mA
I
SW
= –1.5A, 0°C ≤ T
A
≤ 125°C and –1.3A, T
A
< 0°C (Note 4) ● 30 45 mA
SHDN Threshold Voltage ● 1.27 1.33 1.40 V
SHDN Input Current (Shutting Down) SHDN = 60mV Above Threshold ● –7 –10 –13 µA
SHDN Threshold Current Hysteresis SHDN = 100mV Below Threshold ● 4710 µA
SYNC Threshold Voltage 1.5 2.2 V
SYNC Input Frequency 1.5 2 MHz
SYNC Pin Resistance I
SYNC
= 1mA 20 kΩ
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
= 0.8V, Boost = V
IN
+ 5V, SHDN, SYNC and switch open unless otherwise noted.
PARAMETER CONDITION MIN TYP MAX UNITS
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LT1767E is guaranteed to meet performance specifications
from 0°C to 125°C. Specifications over the –40°C to 125°C operating
junction temperature range are assured by design, characterization and
correlation with statistical process controls.
Note 3: Minimum input voltage is defined as the voltage where the internal
regulator enters lockout. Actual minimum input voltage to maintain a
regulated output will depend on output voltage and load current. See
Applications Information.
Note 4: Current flows into the BOOST pin only during the on period of the
switch cycle.
TYPICAL PERFORMANCE CHARACTERISTICS
UW
TEMPERATURE (°C)
–50
–25 0 25 50 75 100 125
FB VOLTAGE (V)
1767 G01
1.22
1.21
1.20
1.19
1.18
SWITCH CURRENT (A)
0 0.5
1 1.5
SWITCH VOLTAGE (mV)
1767 G02
400
350
300
250
200
150
100
50
0
125°C
25°C
–40°C
FB vs Temperature (Adj) Switch On Voltage Drop Oscillator Frequency
TEMPERATURE (°C)
–50
–25 0 25 50 75 100 125
FREQUENCY (MHz)
1767 G03
1.50
1.45
1.40
1.35
1.30
1.25
1.20
1.15
1.10