LT1939IDD Ver la hoja de datos (PDF) - Linear Technology
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LT1939IDD Datasheet PDF : 24 Pages
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LT1939
TYPICAL PERFORMANCE CHARACTERISTICS
Boost Current vs Switch Current
50
45
40
150°C
35
–50°C
30
25
20
25°C
15
10
5
0
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
SWITCH CURRENT (A)
1939 G19
LDRV Dropout Voltage vs
Temperature
1.50
ILDRV = 5mA
1.45
1.40
1.35
1.30
1.25
1.20
1.15
1.10
1.05
1.00
–50 –25 0 25 50 75 100 125 150
TEMPERATURE (°C)
1939 G22
Minimum Boost Voltages vs
Temperature
2.7
2.5
2.3
2.1
MINIMUM BOOST FOR
SWITCH SATURATION
1.9
1.7
1.5
–50 –25 0 25 50 75 100 125 150
TEMPERATURE (°C)
1939 G20
Switcher Dropout Operation
6
IOUT1 = 1A
5
VOUT1 = 5V
4
VOUT1 = 3.3V
3
2
1
0
2.5 3.0 3.5 4.0 4.5 5.0 5.5
INPUT VOLTAGE (V)
1939 G23
Minimum Input Voltage
8
7
6
VOUT1 = 5V
5
4
VOUT1 = 3.3V
3
2
1 FSW = 1MHz
0 L = 3.3μH
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
LOAD CURRENT (A)
1939 G21
Inductor Value for 2A Maximum
Load Current (VOUT = 3.3V,
IRIPPLE = 250mA)
2500
L = 1μH
2250
L = 1.5μH
2000
1750
L = 2.2μH
1500
1250
L = 3.3μH
1000
750
500
250
5
L = 4.7μH
L = 6.8μH
L = 10μH
10
15
20
INPUT VOLTAGE (V)
25
1939 G24
PIN FUNCTIONS
VIN (Pin 1): The VIN pin powers the internal control circuitry
and is monitored by an undervoltage comparator. The VIN
pin is also connected to the collectors of the internal power
NPN switch and linear output NPN. The VIN pin has high
dI/dt edges and must be decoupled to ground close to
the pin of the device.
SHDN (Pin 2): The SHDN pin is used to shut down the
LT1939 and reduce quiescent current to a typical value
of 12μA. The accurate 0.76V threshold and input current
hysteresis can be used as an undervoltage lockout, prevent-
ing the regulator from operating until the input voltage has
reached a predetermined level. Force the SHDN pin above
its threshold or let it float for normal operation.
SS (Pin 3): The SS pin is used to control the slew rate
of the output of both the switching and linear regulators.
A single capacitor from the SS pin to ground determines
the regulators’ ramp rate. For soft-start details see the
Applications Information section.
1939f
6
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