|
|
PDF LT3487 Data sheet ( Hoja de datos )
| Número de pieza | LT3487 | |
| Descripción | Boost and Inverting Switching Regulator | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
|
Hay una vista previa y un enlace de descarga de LT3487 (archivo pdf) en la parte inferior de esta página. Total 16 Páginas | ||
|
No Preview Available !
FEATURES
■ Generates 15V at 45mA, –8V at 90mA from a
Li-Ion Cell
■ Output Disconnect
■ Sequencing: Positive Output Reaches Regulation
Before Negative Channel Begins Switching
■ Internal Schottky Diodes
■ 2MHz Constant Switching Frequency
■ Requires Only One Resistor per Channel to Set
Output Voltages
■ VIN Range: 2.3V to 16V
■ Output Voltage Up to 28V
■ Short-Circuit Robust
■ Capacitor Programmable Soft-Start
■ Separate VBAT Pin Allows Separate Sources for
Power and Control Circuitry
■ Available in 10-Lead (3mm × 3mm) DFN Package
U
APPLICATIO S
■ CCD Bias
■ TFT LCD Bias
■ OLED Bias
■ ±Rail Generation for Op Amps
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
LT3487www.DataSheet4U.com
Boost and Inverting
Switching Regulator
for CCD Bias
DESCRIPTIO
The LT®3487 dual channel switching regulator generates
positive and negative outputs for biasing CCD imagers.
The device delivers up to –8V at 90mA and 15V at 45mA
from a lithium-ion cell, providing bias for many popular
CCD imagers. The boost regulator incorporates output
disconnect technology to eliminate the DC current path
from VIN to the output load that is present in standard
boost configurations. The 2MHz switching frequency
allows CCD solutions using tiny, low profile capacitors
and inductors and generates low noise outputs that are
easy to filter. Schottky diodes are internal and the output
voltages are set with one resistor per channel, reducing
the external component count.
Intelligent soft-start allows sequential soft-start of the two
channels with a single capacitor. The soft-start is sequenced
such that the output ramp of the negative channel begins
after the ramp of the positive channel. Internal sequencing
circuitry also disables the negative channel until the positive
channel has reached 87% of its final value, ensuring that
the sum of the two outputs is always positive.
The LT3487 is available in a 10-pin 3mm × 3mm DFN
package.
TYPICAL APPLICATIO
VIN
3V TO 12V
2.2µF
1µF
15µH
47pF
VNEG
–8V
90mA
324k
RUN/SS
22µF
100nF
15µH
10µH
SWN
VIN
DN
VBAT
LT3487
SWP
CAP
FBP
FBN
RUN/SS
GND
VPOS
549k 100nF
4.7µF
3487 TA01a
VPOS
15V
45mA
Conversion Efficiency
80 POS CHANNEL AT CAP
75
70
POS CHANNEL
65 AT VPOS
60 NEG CHANNEL
55
50
45
40
0
VIN = 3.6V
20 40 60 80
LOAD CURRENT (mA)
100
3487 TA01b
3487f
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LT3487www.DataSheet4U.com
Output Disconnect Current Limit
200
VCAP = 15V
VBAT = 3.6V
VPOS = 0V
175
150
125
100
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3487 G12
Switch Current Limits vs RUN/SS
Voltage (at 55% Duty Cycle)
1000
NEG CHANNEL
800
P0S CHANNEL
600
400
200
Switch Current Limits
1200
1150
1100
NEG CHANNEL
1050
1000
950
POS CHANNEL
900
850
800
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3487 G13
RUN/SS Pin Current in Shutdown
3.0
2.5
2.0
1.5
1.0
0.5
Switch Current Limits
vs Duty Cycle
1200
1000
NEG CHANNEL
800
P0S CHANNEL
600
400
200
0
0 20 40 60 80 100
DUTY CYCLE (%)
3487 G14
RUN/SS Pin Current
vs VIN in Shutdown
2.0
1.5
1.0
0.5
0
0 250 500 750 1000 1250 1500
RUN/SS (mV)
3487 G15
UVLO Voltage
2.5
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3487 G16
0
2 4 6 8 10 12 14 16
VIN (V)
3487 G17
RUN/SS Shutdown Threshold
300
2.4 250
200
2.3
150
2.2
100
2.1 50
2.0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3487 G18
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3487 G19
3487f
5
5 Page 
LT3487www.DataSheet4U.com
APPLICATIO S I FOR ATIO
Choosing a Feedback Node
The positive channel feedback resistor, R1, may be con-
nected to the VPOS pin or to the CAP pin (see Figure 5).
Regulating the VPOS pin eliminates the output offset result-
ing from the voltage drop across the output disconnect.
However, in the case of a short-circuit fault at the VPOS
pin, the LT3487 will switch continuously because the FBP
pin is low. While operating in this open-loop condition, the
rising voltage at the CAP pin is limited only by the current
limit of the output disconnect. Given worst-case parameters
this voltage may reach 18V in a Li-Ion application. Care
must be taken in high VIN applications when regulating
from the VPOS pin. When the short-circuit is removed, the
VPOS pin will bounce up to the voltage on the CAP pin,
potentially exceeding the programmed output voltage until
300
250
200
150
100
50
0
0 20 40 60 80 100
DISCONNECT CURRENT (mA)
2400 G31
Figure 4. VCE vs I of Output Disconnect
the capacitor voltages fall back into regulation. While this
is harmless to the LT3487, this should be considered in
the context of the external circuitry if short-circuit events
are expected. Regulating the CAP pin ensures that the
voltage on the VPOS pin never exceeds the set output volt-
age after a short-circuit event. However, this setup does
not compensate for the voltage drop across the output
disconnect, resulting in an output voltage that is slightly
lower than the voltage set by the feedback resistor. This
voltage drop (VDISC) can be accounted for when using
the CAP pin as the feedback node by setting the output
voltage according to the following formula (using VDISC
from Figure 4):
R1= VPOS + VDISC – 1.23
25µA
VBAT
The VBAT pin is a new innovation in the LT3487 that allows
output disconnect operation in a wide range of applica-
tions. The VBAT pin allows the part to stay on until CAP is
less than 1.2V above VBAT. This ensures that the positive
bias doesn’t fall before the negative bias discharges. In
some applications it may be useful to power the inductors
from a different source than VIN. In this case, connect
VBAT to the source powering the inductors to allow proper
operation of the disconnect. For example, in an automotive
system there may already be a buck regulator producing
3.3V from a 12V battery. The LT3487 enables the user
to power VIN from the 3.3V rail, but power the VBAT pin
SWN
VIN
VBAT
SWP
CAP
LT3487
DN FBP
FBN
RUN/SS
GND
VPOS
VPOS
SWN
VIN
VBAT
SWP
CAP
LT3487
DN FBP
FBN
RUN/SS
GND
VPOS
VPOS
3487 F05
Figure 5. Feedback Connection Using the VPOS and CAP Pins
3487f
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT3487.PDF ] | |
Hoja de datos destacado
| Número de pieza | Descripción | Fabricantes |
| LT3480 | 2.4MHz Step-Down Switching Regulator | Linear Technology |
| LT3481 | 2.2.8MHz Step-Down Switching Regulator | Linear Technology |
| LT3482 | 90V Boost DC/DC Converter | Linear Technology |
| LT3483 | Inverting Micropower 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 |