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PDF ( 数据手册 , 数据表 ) 317B

零件编号 317B
描述 Micropower/ 600kHz PWM DC/DC Converters
制造商 Linear Technology
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317B 数据手册, 描述, 功能
LT1317/LT1317B
Micropower, 600kHz PWM
DC/DC Converters
FEATURES
s 100µA Quiescent Current
s Operates with VIN as Low as 1.5V
s 600kHz Fixed Frequency Operation
s Starts into Full Load
s Low-Battery Detector Active in Shutdown
s Automatic Burst Mode Operation at
Light Load (LT1317)
s Continuous Switching at Light Loads (LT1317B)
s Low VCESAT Switch: 300mV at 500mA
s Pin for Pin Compatible with the LT1307/LT1307B
U
APPLICATIONS
s Cellular Telephones
s Cordless Telephones
s Pagers
s GPS Receivers
s Battery Backup
s Portable Electronic Equipment
s Glucose Meters
s Diagnostic Medical Instrumentation
TYPICAL APPLICATION
L1
10µH
D1
+
C1
47µF
2 SHUTDOWN
CELLS
VIN SW
LBI FB
LT1317
SHDN
VC
LBO
GND
RC
33k
CC
3.3nF
R1
1M
1% +
R2*
604k
1%
3.3V
200mA
C2
47µF
D1: MBR0520
L1: SUMIDA CD43-100
* FOR 5V OUTPUT, R2 = 332k, 1%
1317 F01
Figure 1. 2-Cell to 3.3V Boost Converter
DESCRIPTION
The LT®1317/LT1317B are micropower, fixed frequency
step-up DC/DC converters that operate over a wide input
voltage range of 1.5V to 12V. The LT1317 features auto-
matic shifting to power saving Burst ModeTM operation at
light loads. High efficiency is maintained over a broad
300µA to 200mA load range. Peak switch current during
Burst Mode operation is kept below 250mA for most
operating conditions which results in low output ripple
voltage, even at high input voltages. The LT1317B does
not shift into Burst Mode operation at light loads, eliminat-
ing low frequency output ripple at the expense of light load
efficiency.
The LT1317/LT1317B contain an internal low-battery de-
tector with a 200mV reference that stays alive when the
device goes into shutdown.
No-load quiescent current of the LT1317 is 100µA and
shuts down to 30µA. The internal NPN power switch
handles a 500mA current with a voltage drop of just
300mV.
The LT1317/LT1317B are available in MS8 and SO-8
packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
2-Cell to 3.3V Converter Efficiency
90
2.2VIN 3VIN
80
1.65VIN
70
60
50
40
0.3 1
10 100
LOAD CURRENT (mA)
1000
1317 TA01
1







317B pdf, 数据表
LT1317/LT1317B
APPLICATIONS INFORMATION
The LT1317B differs from the LT1317 in that the bias point
on A1 is set lower than on the LT1317 so that minimum
switch current can drop below 50mA. Because A1’s bias
point is set lower, there is no Burst Mode operation at light
loads and the device continues switching at constant
frequency. This results in the absence of low frequency
output voltage ripple at the expense of light load efficiency.
The difference between the two devices is clearly illus-
trated in Figure 2. The top two traces in Figure 2 show an
LT1317/LT1317B circuit, using the components indicated
in Figure 1, set to a 3.3V output. Input voltage is 2V. Load
current is stepped from 2mA to 200mA for both circuits.
Low frequency Burst Mode operation voltage ripple is
observed on Trace A, while none is observed on Trace B.
TRACE A
TRACE B
LT1317
VOUT
100mV/DIV
AC COUPLED
LT1317B
VOUT
100mV/DIV
AC COUPLED
ILOAD
200mA
2mA
1ms/DIV
1317 F02
Figure 2. LT1317 Exhibits Ripple at 2mA Load
During Burst Mode Operation, the LT1317B Does Not
LAYOUT HINTS
The LT1317 switches current at high speed, mandating
careful attention to layout for proper performance. You
will not get advertised performance with careless layouts.
Figure 3 shows recommended component placement.
Follow this closely in your PC layout. Note the direct path
of the switching loops. Input capacitor CIN must be placed
close (< 5mm) to the IC package. As little as 10mm of wire
or PC trace from CIN to VIN will cause problems such as
inability to regulate or oscillation.
GROUND PLANE
18
2 LT1317 7
36
45
L
VIN
MULTIPLE
VIAs
CIN
COUT
D
GND
VOUT
1317 F03
Figure 3. Recommended Component Placement. Traces Carrying
High Current Are Direct. Trace Area at FB Pin and VC Pin is Kept
Low. Lead Length to Battery Should be Kept Short.
COMPONENT SELECTION
Inductors
Inductors appropriate for use with the LT1317 must
possess three attributes. First, they must have low core
loss at 600kHz. Most ferrite core units have acceptable
losses at this switching frequency. Inexpensive iron pow-
der cores should be viewed suspiciously, as core losses
can cause significant efficiency penalties at 600kHz. Sec-
ond, the inductor must be able to handle peak switch
current of the LT1317 without saturating. This places a
lower limit on the physical size of the unit. Molded chokes
or chip inductors usually do not have enough core to
support the LT1317 maximum peak switch current and are
unsuitable for the application. Lastly, the inductor should
have low DCR (copper wire resistance) to prevent effi-
ciency-killing I2R losses. Linear Technology has identified
several inductors suitable for use with the LT1317. This is
not an exclusive list. There are many magnetics vendors
whose components are suitable for use. A few vendor’s
components are listed in Table 1.
8







317B equivalent, schematic
LT1317/LT1317B
TYPICAL APPLICATION
Digital Camera Power Supply
10k
4 AA
CELLS
(3.2V TO
6.5V)
SHUTDOWN
24V
+ C1
22µF
10V
T1 7
LC
8
5
LPRI:15µH 2
LB
6
3
LA
14
D3
D2
D1
+
+ C5
10µF
35V
18V
3mA
+ C4
22µF
10V
5V
20mA
C2
100µF
6V
3.3V
150mA
C3
1µF, 16V
VIN SW
LT1317
1M
SHDN
FB
VC GND
10k
3300pF
604k
1317 TA10
C1, C4: AVX TPSC226M016
C2: AVX TPSC106M006
C3: CERAMIC (i.e. AVX, MANY OTHERS)
C5: SANYO 35CV10GX
D1, D2: MBR0520LT1 (MOTOROLA) OR EQUIVALENT
D3: MMBD914LT1 (MOTOROLA) OR EQUIVALENT
T1: COILTRONICS CTX02-14272-X1
RELATED PARTS
PART NUMBER
LTC®1163
LTC1174
LT1302
LT1304
LT1307
LTC1440/1/2
LTC1516
LT1521
DESCRIPTION
Triple High Side Driver for 2-Cell Inputs
Micropower Step-Down DC/DC Converter
High Output Current Micropower DC/DC Converter
2-Cell Micropower DC/DC Converter
Single Cell Micropower 600kHz PWM DC/DC Converter
Ultralow Power Single/Dual Comparators with Reference
2-Cell to 5V Regulated Charge Pump
Micropower Low Dropout Linear Regulator
COMMENTS
1.8V Minimum Input, Drives N-Channel MOSFETs
94% Efficiency, 130µA IQ, 9V to 5V at 300mA
5V/600mA from 2V, 2A Internal Switch, 200µA IQ
Low-Battery Detector Active in Shutdown
3.3V at 75mA from 1 Cell, MSOP Package
2.8µA IQ, Adjustable Hysteresis
12µA IQ, No Inductors, 5V at 50mA from 3V Input
500mV Dropout, 300mA Current, 12µA IQ
16 Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 q FAX:(408)434-0507 q www.linear-tech.com
13177bf LT/TP 1198 4K • PRINTED IN THE USA
© LINEAR TECHNOLOGY CORPORATION 1998










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