|
|
PDF LT1939 Data sheet ( Hoja de datos )
| Número de pieza | LT1939 | |
| Descripción | Monolithic 2A Step-Down Regulator Plus Linear Regulator/Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LT1939 (archivo pdf) en la parte inferior de esta página. Total 24 Páginas | ||
|
No Preview Available !
FEATURES
n Wide Input Range: 3V to 25V
n Short-Circuit Protected Over Full Input Range
n 2A Output Current Capability
n Adjustable/Synchronizable Fixed Frequency
Operation from 250kHz to 2.2MHz
n Soft-Start/Tracking Capability
n Output Adjustable Down to 0.8V
n Adjustable Linear Regulator/Driver with 13mA
Output Capability
n Power Good Comparator with Complementary
Outputs
n Low Shutdown Current: 12μA
n Thermally Enhanced 3mm × 3mm DFN Package
APPLICATIONS
n Automotive Battery Regulation
n Industrial Control
n Wall Transformer Regulation
n Distributed Power Regulation
LT1939www.DataSheet4U.com
Monolithic 2A Step-Down
Regulator Plus Linear
Regulator/Controller
DESCRIPTION
The LT®1939 is a current mode PWM step-down DC/DC
converter with an internal 2.3A switch. The wide input
range of 3V to 25V makes the LT1939 suitable for regu-
lating power from a wide variety of sources, including
automotive batteries, industrial supplies and unregulated
wall adapters.
Resistor-programmable 250kHz to 2.2MHz frequency
range and synchronization capability enable optimization
between efficiency and external component size. Cycle-
by-cycle current limit, frequency foldback and thermal
shutdown provide protection against a shorted output.
The soft-start feature controls the ramp rate of the output
voltage, eliminating input current surge during start-up,
and also provides output tracking.
The LT1939 contains an internal NPN transistor with feed-
back control which can be configured as a linear regulator
or as a linear regulator controller.
The LT1939’s low current shutdown mode (<12μA) 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
Dual Step-Down Converters
VIN
6V TO 25V
2.2μF
0.47μF
VIN BST
LT1939
SW
SHDN
SS
FB
PG
PG
BAT54
0.47μF
6.8μH
B240A
42.2k
8.06k
VOUT1
5V
1A
22μF
53.6k
330pF
40.2k
RT/SYNC LDRV
VC
LFB
1k
24.9k
8.06k
VOUT2
3.3V
22μF 1A
1939 TA01a
Switching Converter Efficiency
90
85
80 VOUT1 = 5V AT 1A
AC COUPLED
75 2mV/DIV
70
65
60
55
VIN = 12V
IOUT2 = 0A
FREQUENCY = 800kHz
50
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 TA01b
VOUT2 = 3.3V AT 1A
AC COUPLED
2mV/DIV
Output Voltage Ripple
500ns/DIV
1939 TA01c
1939f
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT1939www.DataSheet4U.com
Power Good Thresholds vs
Temperature
0.75
0.74
0.73
RISING EDGE
0.72
0.71
0.70
FALLING EDGE
0.69
0.68
0.67
0.66
0.65
–50 –25 0 25 50 75 100 125 150
TEMPERATURE (°C)
1939 G10
Peak Switch Current vs
Temperature
3.5
3.4
3.3
3.2
3.1
3.0
2.9
2.8
2.7
2.6
2.5
–50 –25 0 25 50 75 100 125 150
TEMPERATURE (°C)
1939 G13
Power Good Sink Currents vs
Temperature
1000
900
PG
800
700
600
PG
500
400
300
200
100
0
–50 –25 0 25 50 75 100 125 150
TEMPERATURE (°C)
1939 G11
LDRV Short-Circuit Current vs
Temperature
20
19
18
17
16
15
14
13
12
11
10
–50 –25 0 25 50 75 100 125 150
TEMPERATURE (°C)
1939 G14
Minimum Switching Times
300
275
250
225
200
175
150 MINIMUM ON TIME
125
100 MINIMUM OFF TIME
75
50
–50 –25 0 25 50 75 100 125 150
TEMPERATURE (°C)
1939 G16
Frequency vs RRT/SYNC
2500
2250
2000
1750
1500
1250
1000
750
500
250
0
0 20 40 60 80 100 120 140 160 180 200
RRT/SYNC (kΩ)
1939 G17
Frequency vs Temperature
600
RRT/SYNC = 90.9k
580
560
540
520
500
480
460
440
420
400
–50 –25 0 25 50 75 100 125 150
TEMPERATURE (°C)
1939 G12
External Sync Duty Cycle Range
vs External Sync Frequency
100
90
MAXIMUM DUTY CYCLE
80
70
60
50
40
30
20
MINIMUM DUTY CYCLE
10
0
250 750 1250 1750 2250
SYNCHRONIZATION FREQUENCY (kHz)
19939 G15
Switch Saturation Voltage vs
Switch Current
600
500
400
300
–50°C
200
25°C
100
150°C
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 G18
1939f
5
5 Page 
LT1939www.DataSheet4U.com
APPLICATIONS INFORMATION
The following example along with the data in Table 1
illustrates the tradeoffs of switch frequency selection.
Example.
VIN = 25V, VOUT1 = 3.3V, IOUT1 = 2A,
Temperature = 0°C to 85°C
tON(MIN) = 185ns (85°C from Typical Characteris-
tics graph), VD = 0.6V, VSW = 0.4V (85°C)
Max
Frequency =
3.3 + 0.6
25 0.4 + 0.6
•
1
185ns
~ 835kHz
RT/SYNC ~ 49.9k
Frequency ≅ 820kHz
Input Voltage Range
Once the switching frequency has been determined, the
input voltage range of the regulator can be determined.
The minimum input voltage is determined by either the
LT1939’s minimum operating voltage of ~2.8V or by its
maximum duty cycle. The duty cycle is the fraction of time
that the internal switch is on during a clock cycle. The
maximum duty cycle can be determined from the clock
frequency and the minimum off time from the typical
characteristics graph.
This leads to a minimum input voltage of:
VIN(MIN)
=
VOUT1 + VD
DCMAX
VD
+
VSW
where VSW is the voltage drop of the internal switch,
and
DCMAX = 1 – tOFF(MIN) • Frequency.
Figure 3 shows a typical graph of minimum input voltage
vs load current for 3.3V and 5V applications.
The maximum input voltage is determined by the absolute
maximum ratings of the VIN and BST pins and by the
frequency and minimum duty cycle.
The minimum duty cycle is defined as:
DCMIN = tON(MIN) • Frequency
Maximum input voltage as:
VIN(MAX)
=
VOUT1 + VD
DCMIN
VD
+
VSW
8
FSW = 1MHz
L = 3.3μH
7
6
5
4
VOUT1 = 5V START-UP
3 VOUT1 = 5V RUNNING
VOUT1 = 3.3V START-UP
VOUT1 = 3.3V RUNNING
2
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 F03
Figure 3. Minimum Input Voltage vs Load Current
Table 1. Efficiency and Size Comparisons for Different RRT/SYNC Values, 3.3V Output
FREQUENCY
RT/SYNC
EFFICIENCY
VIN(MAX)
L
2.5MHz
15k
73.6
12
1μ
2.0MHz
20k
81.5
14
1.5μ
1.5MHz
24.9k
84.5
18
2.2μ
1.0MHz
40.2k
87.3
25
3.3μ
500kHz
90.9k
88.9
25
4.7μ
C C + L AREA
(mm2)
10μ 24
10μ 24
10μ 24
22μ 34
47μ 40
1939f
11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LT1939.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LT1930 | 1A/ 1.2MHz/2.2MHz/ Step-Up DC/DC Converters | Linear Technology |
| LT1930 | Constant-Current/ Constant-Voltage 1.4MHz Step-Up DC/DC Converter | Linear Technology |
| LT1930A | 1A/ 1.2MHz/2.2MHz/ Step-Up DC/DC Converters | Linear Technology |
| LT1930A | Constant-Current/ Constant-Voltage 1.4MHz Step-Up DC/DC Converter | Linear Technology |
| Número de pieza | Descripción | Fabricantes |
| SLA6805M | High Voltage 3 phase Motor Driver IC. |
 Sanken |
| SDC1742 | 12- and 14-Bit Hybrid Synchro / Resolver-to-Digital Converters. |
 Analog Devices |
|
DataSheet.es es una pagina web que funciona como un repositorio de manuales o hoja de datos de muchos de los productos más populares, |
| DataSheet.es | 2020 | Privacy Policy | Contacto | Buscar |