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PDF LT1501IS8 Data sheet ( Hoja de datos )
| Número de pieza | LT1501IS8 | |
| Descripción | Adaptive-Frequency Current Mode Switching Regulators | |
| Fabricantes | Linear Technology | |
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LT1500/LT1501
Adaptive-Frequency
Current Mode Switching Regulators
FEATURES
s Low Noise Adaptive-Frequency Current Mode
Operation Avoids Low Frequency Noise at
Most Load Currents
s Can Be Externally Synchronized (LT1500)
s Micropower Quiescent Current: 200µA
s Shutdown Current: 8µA Typ
s Internal Loop Compensation
s Low-Battery Comparator Active in Shutdown
s Minimum Input Voltage: 1.8V Typ
s Additional Negative Voltage Feedback Pin (LT1500)
s Up to 500kHz Switching Frequency
s Uses Low Profile, Low Cost Surface Mount Inductors
U
APPLICATIONS
s Portable Instrumentation
s Battery Operated Systems
s PDA’s
s Standby Power
DESCRIPTION
The LT®1500 is an adaptive-frequency current mode step-
up switching regulator with an internal power switch that
is rated up to 700mA. In contrast to pulse skipping
switching regulators, the LT1500 uses a current mode
topology that provides lower noise operation and im-
proved efficiency. Only at very light loads is Burst ModeTM
activated to give high efficiency and micropower opera-
tion. High switching frequency (up to 500kHz) allows very
small inductors to be used, along with ceramic capacitors
if desired.
The LT1500 operates with input voltages from 1.8V to 15V
and has only 200µA operating current dropping to 8µA in
shutdown. A low-battery comparator is included which
stays alive in shutdown. A second output feedback pin
with negative polarity allows negative output voltages to
be regulated when the switcher is connected up as a Cuk
or a flyback converter.
Two package types are available. The LT1500 comes in a
14-pin SO package, with two options available for fixed
output (3.3V or 5V) or adjustable operation. A reduced
feature part, the LT1501, comes in the smaller 8-pin SO
package with internal frequency compensation. It is also
available in adjustable and fixed output voltage versions.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
TYPICAL APPLICATION
2-Cell to 5V Converter
D1
22µH† MBR0520L
5V, 200mA
2 EACH
NiCd OR
ALKALINE
CELLS
301k
1%
+ 33µF*
6V
VIN ISENSE
SHDN
LT1501-5
LBI
SW
OUT
301k
1% LBO GND
1nF
+ 220µF**
10V
TANT
* AVX, TPSC107M006R0150
** AVX, TPSD107M010 R0100
† SUMIDA CD73-220, CD54-220
OR CD43-220. SELECT ACCORDING
TO MAXIMUM LOAD CURRENT
LOW-BATTERY FLAG
(USE EXTERNAL PULL-UP)
LT1500/01 • TA01
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LT1500/LT1501
Efficiency (3.3V Output)
100
90
ILOAD = 100mA
80 ILOAD = 10mA
70
60
50 TJ = 25°C
L = 33µH
LOW LOSS INDUCTOR
40
1.75 2.00 2.25 2.50 2.75 3.00 3.25
INPUT VOLTAGE (V)
LT1500/01 • TPC11
Inductor Copper Loss
(3.3V Output)
10
R = 1Ω
R = 0.5Ω
R = 0.2Ω
1 R = 0.1Ω
Efficiency (5V Output)
100
90 ILOAD = 10mA
ILOAD = 100mA
80
70
60
50 TJ = 25°C
L = 33µH
LOW LOSS INDUCTOR
40
2.0 2.5 3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
LT1500/01 • TPC12
Inductor Copper Loss (5V Output)
10
VIN = 3V
R = 1Ω
R = 0.5Ω
R = 0.2Ω
1 R = 0.1Ω
Efficiency (12V Output)
100
90 ILOAD = 50mA
80 ILOAD = 10mA
70
60
50 TJ = 25°C
L = 33µH
LOW LOSS INDUCTOR
40
0 2 4 6 8 10 12
INPUT VOLTAGE (V)
LT1500/01 • TPC13
Inductor Copper Loss
(12V Output)
10
VIN = 5V
R = 1Ω
R = 0.5Ω
1 R = 0.2Ω
VIN = 2.3V
0.1
0
50 100 150 200
LOAD CURRENT (mA)
250
300
LT1500/01 • TPC14
Maximum Load Current
(3.3V Output)
600
500
400
L ≥ 33µH
300 L = 10µH
200
100
0
1.50 1.75 2.00 2.25 2.50
INPUT VOLTAGE (V)
2.75 3.00
LT1500/01 • TPC08
0.1
0
50 100 150 200 250 300
LOAD CURRENT (mA)
LT1500/01 • TPC15
Maximum Load Current
(5V Output)
600
500
400
L ≥ 33µH
300
L = 10µH
200
100
0
2.0
2.5 3.0 3.5 4.0 4.5 5.0
INPUT VOLTAGE (V)
LT1500/01 • TPC09
0.1
0 25 50 75 100 125 150 175 200
LOAD CURRENT (mA)
LTC1500/01 • TPC16
Maximum Load Current
(12V Output)
600
500
L = 33µH
400
300 L = 100µH
200 L = 10µH
100
0
0 2 4 6 8 10 12
INPUT VOLTAGE (V)
LT1500/01 • TPC10
5
5 Page 
LT1500/LT1501
APPLICATIONS INFORMATION
type TPS from AVX, or type 595D from Sprague. These
have an ESR of 0.06Ω in a “E” case size. At lower output
current levels, a 100µF unit in a “D” case size may be
sufficient. Output ripple voltage can be calculated from:
VRIPPLE
=
ESR
0.1+
1.2(IOUT )(VOUT
VIN
)
Loop frequency stability is affected by the characteristics
of the output capacitor. The ESR of the capacitor should be
very low, and the capacitance must be large (> 200µF) to
ensure good loop stability under worst-case conditions of
low input voltage, higher output voltages, and high load
currents. The 14-pin LT1500 can use external frequency
compensation on the VC pin to give good loop stability with
smaller output capacitors. See Loop Stability section for
details.
Precautions regarding solid tantalum capacitors for input
bypassing do not apply to the output capacitor because
turn-on surges are limited by the inductor and discharge
surges do not harm the capacitors.
Setting Output Voltage
Preset 3.3V and 5V parts are available. For other voltage
applications the adjustable part uses an external resistor
divider to set output voltage. Bias current for the feedback
(FB) pin is typically ±30nA (it is internally compensated).
Thevenin divider resistance should be 100kΩ or less to
keep bias current errors to a minimum. This leads to a
value for R1 and R2 (see Figure 1) of:
R1= 100kΩ(VOUT )
1.265V
R2 = R1(1.265)
VOUT – 1.265
Example: VOUT = xxV
R1
=
100kΩ(12)
1.265
= 949k
(use 1M)
R2 = 1M(1.265) = 118k
12 – 1.265
Note that there is an internal switch that disconnects the
internal divider for fixed 3.3V and 5V parts in shutdown.
This prevents the divider from adding to shutdown cur-
rent. Without this switch, shutdown current increases
because of the divider current directly, but even more so
if the FB pin is held above 0.6V by the divider. See graphs
in Typical Performance Characteristics.
VOUT = 12V
R1
1M
FB 1%
ERROR
AMPLIFIER
1.265V
R2
118K
1%
LTC1500/01 • F01
Figure 1. External Voltage Divider
Selectable Output (Fixed Voltage Parts)
The Select pin (available only on LT1500-3/5) allows the
user to select either a 3.3V or 5V output. Floating the pin
sets output voltage at 3.3V and grounding the pin sets
output voltage at 5V. The equivalent circuit of the Select
pin function is shown in Figure 2.
VOUT
204k
ERROR
AMPLIFIER
69k
SELECT
1.265V
58k
GND
LTC1500/01 • F02
Figure 2. Schematic of Select Pin Function
Note that there is a switch in series with the VOUT pin. This
switch is turned off in shutdown to eliminate shutdown
current drawn by the voltage divider. For adjustable parts
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LT1501IS8.PDF ] | |
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