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PDF LT1620IGN Data sheet ( Hoja de datos )
| Número de pieza | LT1620IGN | |
| Descripción | Rail-to-Rail Current Sense Amplifier | |
| Fabricantes | Linear Technology | |
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LT1620/LT1621
Rail-to-Rail Current
Sense Amplifier
FEATURES
s Accurate Output Current Programming
s Usable in Charging Applications Up to 32V Output
s Programmable Load Current Monitor for End-of-
Charging-Cycle Notification (16-Pin Version)
s Dual Function IC (LT1621) Allows Convenient
Integration of Load and Input Current Sensing
s Level-Shifted Current Sense Output for Current Mode
PWM Controllers
s Can be Used for NiCd, NiMH, Lead-Acid and Lithium-
Ion Battery Charging
s Greater than 96% Efficiency Possible in Charger
Applications
s High Output Currents Possible: > 10A
Easily Obtained
APPLICATI S
s High Current Battery Chargers
s High Output Voltage DC/DC Converters
s Constant Current Sources
s Overcurrent Fault Protectors
DESCRIPTIO
The LT ®1620 simplifies the design of high performance,
controlled current battery charging circuits when used in
conjunction with a current mode PWM controller IC.
The LT1620 regulates average output current independent
of input and output voltage variations. Output current can
be easily adjusted via a programming voltage applied to
the LT1620’s PROG pin.
Most current mode PWM controllers have limited output
voltage range because of common mode limitations on the
current sense inputs. The LT1620 overcomes this restric-
tion by providing a level-shifted current sense signal,
allowing a 0V to 32V output voltage range.
The 16-pin version of the LT1620 contains a program-
mable low charging current flag output. This output flag
can be used to signal when a Li-Ion battery charging cycle
is nearing completion.
The LT1621 incorporates two fully independent current
control circuits for dual loop applications.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATI
VIN
LTC1435
SYNCHRONOUS
BUCK
REGULATOR
(VBATT + 0.5V) TO 32V
+ 22µF
35V
×2
VIN
IBATT TO 4A
6 0.1µF
1
VCC
SENSE
AVG
8
2 IOUT
PROG 7
LT1620MS8
3
GND
4 IN–
IN+ 5
ITH SW
SENSE–
27µH 0.025Ω
INTVCC
FB
0.1µF
3k
1%
15.75k
1%
1.43M
0.1%
+
110k
0.1%
22µF
35V
SIMPLIFIED SCHEMATIC. SEE FIGURE 2 FOR COMPLETE SCHEMATIC
LT1620/21 • F01
Figure 1. Low Dropout, High Current Li-Ion Battery Charger
VBATT
100
VIN = 24V
95
90
85
Efficiency
VBATT = 16V
VBATT = 12V
VBATT = 6V
80
75
0
1 2 34
BATTERY CHARGE CURRENT (A)
5
1620/21 • TA02
1
1 page  
U
OPERATION (Refer to the Functional Block Diagram)
used as integration nodes to facilitate averaging of the
current sense amplifier signal. (Note: filter capacitors on
these pins should bypass to the VCC supply.) Integration
of these signals enables direct sensing and control of DC
load current, eliminating the inclusion of ripple current in
load determination.
Transconductance Amplifier
The transconductance amplifier converts the difference
between the current programming input voltage (VPROG)
and the average current sense output (VAVG) into a current
at the amplifier output pin (IOUT). The amplifier output is
unidirectional and only sinks current. The amplifier is
designed to operate at a typical output current of 130µA
LT1620/LT1621
with VAVG = VPROG. In typical PWM/charger type applica-
tions, the IOUT current is used to servo the current control
loop on the mated PWM controller IC to maintain a
programmed load current.
Comparator
The comparator circuit (available only in the LT1620GN)
may be used as an end-of-cycle sensor in a Li-Ion battery
charging system. The comparator detects when the charg-
ing current has fallen to a small value (typically 20% of the
maximum charging current). The comparator drives an open
collector output (MODE) that pulls low when the VAVG2
voltage is more positive than VPROG2 (output current below
the programmed threshold).
APPLICATIONS INFORMATION
In Figure 2, an LT1620MS8 is coupled with an LTC1435
switching regulator in a high performance lithium-ion
battery charger application. The LTC1435 switching regu-
lator delivers extremely low dropout as it is capable of
approximately 99% duty cycle operation. No additional
power supply voltage is required for the LT1620 in this
application; it is powered directly from a 5V local supply
generated by the LTC1435. The DC charge current control
and high common mode current sense range of the
LT1620 combine with the low dropout capabilities of the
LTC1435 to make a 4-cell Li-Ion battery charger with over
96% efficiency, and only 0.5V input-to-output drop at 3A
charging current. Refer to the LTC1435 data sheet (available
from the LTC factory) for additional information on IC func-
tionality, performance and associated component selection.
This LT1620/LTC1435 battery charger is designed to yield
a 16.8V float voltage with a battery charge current of 3.2A.
The VIN supply can range from 17.3V to 28V (limited by the
switch MOSFETs). The charger provides a constant 3.2A
charge current until the battery voltage reaches the pro-
grammed float voltage. Once the float voltage is achieved,
a precision voltage regulation loop takes control, allowing
the charge current to fall as required to complete the
battery charge cycle.
RSENSE Selection
The LT1620 will operate throughout a current program-
ming voltage (VPROG) range of 0V to – 1.25V (relative to
VCC), however, optimum accuracy will be obtained with a
current setting program voltage of – 0.8V, corresponding
to 80mV differential voltage across the current sense
amplifier inputs. Given the desired current requirement,
selection of the load current sense resistor RSENSE is
possible. For the desired 3.2A charge current;
RSENSE = 80mV/3.2A or 0.025Ω
At the programmed 3.2A charge current, the sense resis-
tor will dissipate (0.08V)(3.20A) = 0.256W, and must be
rated accordingly.
Current Sense
The current sense inputs are connected on either side of
the sense resistor with IN+ at the more positive potential,
given average charging current flow. The sense resistor to
IN+, IN– input paths should be connected using twisted
pair or minimum PC trace spacing for noise immunity.
Keep lead lengths short and away from noise sources for
best performance.
5
5 Page 
LT1620/LT1621
U
PACKAGE DESCRIPTIO Dimensions in inches (millimeters) unless otherwise noted.
GN Package
16-Lead Plastic SSOP (Narrow 0.150)
(LTC DWG # 05-08-1641)
0.189 – 0.196*
(4.801 – 4.978)
16 15 14 13 12 11 10 9
0.0075 – 0.0098
(0.191 – 0.249)
0.015
(0.38
±
±
0.004
0.10)
×
45°
0.053 – 0.069
(1.351 – 1.748)
0° – 8° TYP
0.016 – 0.050
(0.406 – 1.270)
0.008 – 0.012
(0.203 – 0.305)
* DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.229 – 0.244
(5.817 – 6.198)
0.004 – 0.009
(0.102 – 0.249)
0.150 – 0.157**
(3.810 – 3.988)
0.025
(0.635)
BSC
1 234 5678
GN16 (SSOP) 0895
MS8 Package
8-Lead MSOP
(LTC DWG # 05-08-1660)
0.118 ± 0.004*
(3.00 ± 0.10)
0.007
(0.18)
0° – 6° TYP
0.040 ± 0.006
(1.02 ± 0.15)
0.006 ± 0.004
(0.15 ± 0.10)
SEATING
0.021 ± 0.004
(0.53 ± 0.01)
PLANE 0.012
(0.30)
0.025
(0.65)
TYP
* DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. MOLD FLASH,
PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
0.192 ± 0.004
(4.88 ± 0.10)
8 76 5
1 234
0.118 ± 0.004**
(3.00 ± 0.10)
MSOP08 0596
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
8 765
0.010
(0.254
–
–
0.020
0.508)
×
45°
0.008 – 0.010
(0.203 – 0.254)
0.053 – 0.069
(1.346 – 1.752)
0°– 8° TYP
0.228 – 0.244
(5.791 – 6.197)
0.004 – 0.010
(0.101 – 0.254)
0.150 – 0.157**
(3.810 – 3.988)
0.016 – 0.050
0.406 – 1.270
0.014 – 0.019
(0.355 – 0.483)
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
0.050
(1.270)
TYP
1 2 34
SO8 0996
Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However,
no responsibility is assumed for its use. Linear Technology Corporation makes no representation that
the interconnection of its circuits as described herein will not infringe on existing patent rights.
11
11 Page | ||
| Páginas | Total 12 Páginas | |
| PDF Descargar | [ Datasheet LT1620IGN.PDF ] | |
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