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PDF LT1936 Data sheet ( Hoja de datos )
| Número de pieza | LT1936 | |
| Descripción | 1.4A 500kHz Step-Down Switching Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LT1936 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
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FEATURES
■ Wide Input Range: 3.6V to 36V
■ Short-Circuit Protected Over Full Input Range
■ 1.9A Guaranteed Minimum Switch Current
■ 5V at 1.4A from 10V to 36V Input
■ 3.3V at 1.4A from 7V to 36V Input
■ 5V at 1.2A from 6.3V to 36V Input
■ 3.3V at 1.2A from 4.5V to 36V Input
■ Output Adjustable Down to 1.20V
■ 500kHz Fixed Frequency Operation
■ Soft-Start
■ Uses Small Ceramic Capacitors
■ Internal or External Compensation
■ Low Shutdown Current: <2μA
■ Thermally Enhanced 8-Lead MSOP Package
APPLICATIONS
■ Automotive Battery Regulation
■ Industrial Control Supplies
■ Unregulated Wall Adapters
LT1936www.DataSheet4U.com
1.4A, 500kHz Step-Down
Switching Regulator
DESCRIPTION
The LT®1936 is a current mode PWM step-down DC/DC
converter with an internal 1.9A power switch, packaged
in a tiny, thermally enhanced 8-lead MSOP. The wide in-
put range of 3.6V to 36V makes the LT1936 suitable for
regulating power from a wide variety of sources, including
automotive batteries, 24V industrial supplies and unregu-
lated wall adapters. Its high operating frequency allows the
use of small, low cost inductors and ceramic capacitors,
resulting in low, predictable output ripple.
Cycle-by-cycle current limit, frequency foldback and
thermal shutdown provide protection against shorted
outputs, and soft-start eliminates input current surge
during start-up. Transient response can be optimized by
using external compensation components, or board space
can be minimized by using internal compensation. The
low current (<2μA) shutdown mode enables easy power
management in battery-powered systems.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other
trademarks are the property of their respective owners.
TYPICAL APPLICATION
VIN
4.5V TO 36V
ON OFF
3.3V Step-Down Converter
VIN BOOST 0.22μF
SHDN
SW
4.7μF
LT1936
COMP
FB
VC GND
10k
10μH
17.4k
VOUT
3.3V
1.2A
22μF
1936 TA01a
95
VIN = 12V
90
Efficiency
VOUT = 5V
85
VOUT = 3.3V
80
75
70
65
0
0.5 1
LOAD CURRENT (A)
1.5
1936 TA01b
1936fd
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT1936www.DataSheet4U.com
Minimum Input Voltage
7.0
VOUT = 5V
TA = 25°C
6.5 L = 15μH
6.0
5.5
5.0
4.5
4.0
1
10 100
LOAD CURRENT (mA)
1000
1936 G13
Minimum Input Voltage
5.0
VOUT = 3.3V
TA = 25°C
L = 10μH
4.5
4.0
3.5
3.0
1
10 100
LOAD CURRENT (mA)
1000
1936 G14
Switch Current Limit
3.0
2.5
2.0
1.5
1.0
0.5
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
1936 G15
Switching Waveforms
VSW
10V/DIV
IL
500mA/DIV
VOUT
20mV/DIV
VIN = 12V
VOUT = 3.3V
IOUT = 1A
L = 10μH
COUT = 22μF
1μs/DIV
1936 G16
Switching Waveforms,
Discontinuous Mode
VSW
10V/DIV
IL
500mA/DIV
VOUT
20mV/DIV
VIN = 12V
VOUT = 3.3V
IOUT = 50mA
L = 10μH
COUT = 22μF
1μs/DIV
1936 G17
VC Voltages
2.5
2.0
CURRENT LIMIT CLAMP
1.5
1.0
SWITCHING THRESHOLD
0.5
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
1936 G18
Error Amp Output Current
60
TA = 25°C
VC = 0.5V
40
20
0
–20
–40
–60
0
1
FB PIN VOLTAGE (V)
2
1936 G19
1936fd
5
5 Page 
LT1936www.DataSheet4U.com
APPLICATIONS INFORMATION
complicated and the best values depend on the application
and in particular the type of output capacitor. A practical
approach is to start with one of the circuits in this data
sheet that is similar to your application and tune the com-
pensation network to optimize the performance. Stability
should then be checked across all operating conditions,
including load current, input voltage and temperature. The
LT1375 data sheet contains a more thorough discussion of
loop compensation and describes how to test the stability
using a transient load.
Figure 1 shows an equivalent circuit for the LT1936 control
loop. The error amplifier is a transconductance amplifier
with finite output impedance. The power section, consisting
of the modulator, power switch and inductor, is modeled
as a transconductance amplifier generating an output
current proportional to the voltage at the VC pin. Note that
the output capacitor integrates this current, and that the
capacitor on the VC pin (CC) integrates the error amplifier
output current, resulting in two poles in the loop. In most
cases a zero is required and comes from either the output
capacitor ESR or from a resistor RC in series with CC.
This simple model works well as long as the value of the
inductor is not too high and the loop crossover frequency
is much lower than the switching frequency. A phase lead
capacitor (CPL) across the feedback divider may improve
the transient response.
Figure 2 compares the transient response across several
output capacitor choices and compensation schemes.
In each case the load current is stepped from 200mA to
800mA and back to 200mA.
COUT = 22μF
(AVX 1210ZD226MAT)
(2a) COMP
VC
VOUT
100mV/DIV
COUT = 22μF ×2
(2b) COMP
VC
COUT = 150μF
(4TPC150M)
(2c) COMP
VC
VOUT
100mV/DIV
VOUT
100mV/DIV
(2d)
COUT = 150μF
(4TPC150M)
COMP
VC
220k
100pF
VOUT
100mV/DIV
800mA
IOUT
500mA/DIV 200mA
50μs/DIV
1936 F02
Figure 2. Transient Load Response of the LT1936 with Different Output
Capacitors as the Load Current is Stepped from 200mA to 800mA. VOUT = 3.3V
1936fd
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LT1936.PDF ] | |
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