LT1620CGN#TR [Linear]
IC SPECIALTY ANALOG CIRCUIT, PDSO16, 0.150 INCH, PLASTIC, SSOP-16, Analog IC:Other;
| 型号： | LT1620CGN#TR |
| 厂家： | 
Linear |
| 描述： | IC SPECIALTY ANALOG CIRCUIT, PDSO16, 0.150 INCH, PLASTIC, SSOP-16, Analog IC:Other 放大器 |
| 文件： | 总12页 (文件大小：286K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
LT1620/LT1621
Rail-to-Rail Current
Sense Amplifier
U
DESCRIPTIO
EATURE
S
F
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.
■
■
■
Accurate Output Current Programming
Usable in Charging Applications Up to 32V Output
Programmable Load Current Monitor for End-of-
Charging-Cycle Notification (16-Pin Version)
Dual Function IC (LT1621) Allows Convenient
Integration of Load and Input Current Sensing
Level-Shifted Current Sense Output for Current Mode
PWM Controllers
TheLT1620regulatesaverageoutputcurrentindependent
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
voltagerangebecauseofcommonmodelimitationsonthe
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.
Can be Used for NiCd, NiMH, Lead-Acid and Lithium-
Ion Battery Charging
Greater than 96% Efficiency Possible in Charger
Applications
High Output Currents Possible: > 10A
Easily Obtained
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.
O U
PPLICATI
A
S
■
High Current Battery Chargers
High Output Voltage DC/DC Converters
Constant Current Sources
■
The LT1621 incorporates two fully independent current
control circuits for dual loop applications.
■
■
Overcurrent Fault Protectors
, LTC and LT are registered trademarks of Linear Technology Corporation.
U
O
TYPICAL APPLICATI
(V
+ 0.5V) TO 32V
BATT
V
IN
V
IN
+
22µF
LTC1435
Efficiency
35V
SYNCHRONOUS
BUCK
100
95
× 2
V
= 24V
IN
I
TO 4A
V
= 16V
= 12V
BATT
BATT
REGULATOR
V
I
SW
BATT
TH
0.025Ω
–
1.43M
0.1%
27µH
SENSE
V
BATT
+
INTV
FB
CC
22µF
35V
90
V
= 6V
BATT
0.1µF
0.1µF
110k
0.1%
6
3k
1%
85
80
75
V
CC
1
2
8
SENSE
AVG
7
5
I
PROG
LT1620MS8
OUT
15.75k
1%
3
4
GND
–
+
IN
IN
0
1
2
3
4
5
LT1620/21 • F01
BATTERY CHARGE CURRENT (A)
SIMPLIFIED SCHEMATIC. SEE FIGURE 2 FOR COMPLETE SCHEMATIC
1620/21 • TA02
Figure 1. Low Dropout, High Current Li-Ion Battery Charger
1
LT1620/LT1621
W W W
U
(Referenced to Ground) (Note 1)
ABSOLUTE AXI U RATI GS
Sense Amplifier Input Common Mode .......–0.3V to 36V
Operating Ambient Temperature Range
Commercial ............................................ 0°C to 70°C
Industrial ............................................ –40°C to 85°C
Storage Temperature Range ................ –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................. 300°C
Power Supply Voltage: VCC ..........................–0.3V to 7V
Programming Voltage:
PROG, PROG2 ............ –0.3V to VCC + 0.3V (7V Max)
I
OUT, SENSE, AVG, AVG2,
MODE Voltage ................ – 0.3V to VCC + 0.3V (7V Max)
W
U
/O
PACKAGE RDER I FOR ATIO
TOP VIEW
TOP VIEW
TOP VIEW
PROG A
AVG A
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
V
CC A
+
SENSE
NC
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
AVG
SENSE
1
2
3
4
8
7
6
5
AVG
IN
IN
A
A
NC
I
PROG
OUT
–
SENSE A
I
PROG
PROG2
AVG2
OUT
GND
V
CC
I
OUT A
GND A
–
+
NC
GND
MODE
NC
IN
IN
GND B
–
I
OUT B
MS8 PACKAGE
8-LEAD PLASTIC MSOP
S8 PACKAGE
8-LEAD PLASTIC SO
θJA = 250°C/W (MS)
θJA = 120°C/W (S)
IN
IN
V
B
B
SENSE B
AVG B
V
CC
+
NC
–
+
PROG B
CC B
IN
IN
ORDER PART NUMBER
GN PACKAGE
GN PACKAGE
16-LEAD PLASTIC SSOP
16-LEAD PLASTIC SSOP
LT1620CS8
LT1620IS8
LT1620CMS8
θJA = 149°C/W
θJA = 149°C/W
ORDER PART NUMBER
ORDER PART NUMBER
LT1620CGN
LT1620IGN
LT1621CGN
LT1621IGN
MS8 PART MARKING
BC
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
+
VIN = 16.8V, VCC = 5V, VIOUT = 2V, TA = 25°C unless otherwise noted.
SYMBOL PARAMETER
Supply
CONDITIONS
MIN
TYP
MAX
UNITS
V
5V Supply Voltage
DC Active Supply Current
LT1620GN
DC Active Supply Current
LT1620S8, LT1620MS8, 1/2 LT1621GN 4.5V ≤ V ≤ 5.5V, IN – IN = 100mV
●
●
●
●
4.5
5.0
2.8
5.5
3.8
4.0
3.3
3.7
1.9
2.1
V
mA
mA
mA
mA
mA
mA
CC
I
SENSE = AVG = PROG = PROG2 = V
CC
CC
+
–
4.5V ≤ V ≤ 5.5V, IN – IN = 100mV
CC
SENSE = AVG = PROG = V
2.3
1.3
CC
–
+
CC
DC Active Supply Current
LT1620S8, LT1620MS8, 1/2 LT1621GN 4.5V ≤ V ≤ 5.5V, IN – IN = 0mV
SENSE = AVG = PROG = V
CC
–
+
CC
Current Sense Amplifier
V
V
Input Common Mode Range
●
●
0
0
32
125
V
mV
CM
ID
Differential Input Voltage Range
0V ≤ V ≤ 32V
CM
+
–
(IN – IN )
V
Input Offset - Measured at ×1 Output
SENSE
V
CC
V
ID
≤ V ≤ 32V
–5
–6
5
6
mV
mV
OSSENSE
CM
= 80mV
(V
)
●
2
LT1620/LT1621
ELECTRICAL CHARACTERISTICS
IN+ = 16.8V, VCC = 5V, VIOUT = 2V, TA = 25°C unless otherwise noted.
SYMBOL PARAMETER
Current Sense Amplifier
CONDITIONS
MIN
TYP
MAX
UNITS
V
Input Offset - Measured at ×10 Output
(V
V
≤ V ≤ 32V
–3
–4
–10
–3
–4
–0.1
3
4
15
3
4
mV
mV
mV
mV
mV
mV
OSAVG
CC
CM
)
35mV ≤ V ≤ 125mV
●
●
AVG
ID
V
V
= 0V, V = 80mV
CM
ID
V
V
Input Offset - Measured at ×20 Output
(V
≤ V ≤ 32V
OSAVG2
CC
CM
)
0V ≤ V ≤ 35mV
0V ≤ V ≤ 32V, V = 0V, Referenced to V
CC
●
●
AVG2
ID
No-Load Output Offset
–3
SENSE
CM
ID
+
–
I
Input Bias Current (Sink)
V
≤ V ≤ 32V (Note 2)
200
185
270
400
430
5.25
5.50
µA
µA
mA
mA
B(IN , IN )
CC
CM
●
●
Input Bias Current (Source)
V
CM
= 0V (Note 2)
4.0
Transconductance Amplifier
g
Amplifier Transconductance
3000
2200
60
3500
80
4000
4800
µmho
µmho
m
●
A
Amplifier Voltage Gain
1V ≤ V
≤ 3V
dB
V
IOUT
V
I
Saturation Limit (Sink)
I
I
I
= 50µA
= 200µA
= 1mA
●
●
●
0.05
0.10
0.35
0.15
0.30
0.65
V
V
V
OLIOUT
OUT
IOUT
IOUT
IOUT
V
PROG Input Range
Input Bias Current
Input Offset Voltage
●
V
– 1.25
V
CC
V
nA
mV
mV
PROG
CC
I
Measured at PROG Pin
= 130µA
20
BPROG
V
I
–7
–8
7
8
OSPROG
IOUT
(V
– V
)
●
●
AVG
PROG
End-of-Cycle Comparator
V
V
PROG2 Input Range
Input Hysteresis
Input Bias Current
V
– 2.5
V – 0.15
CC
V
mV
nA
PROG2
HYST
CC
Measured at AVG2 Pin
Measured at PROG2 Pin
15
20
I
BPROG2
V
Output Logic Low Output (Sink)
I
I
= 0.5mA
= 10mA
●
●
0.1
0.5
0.5
1.2
V
V
OLMODE
MODE
MODE
The
● denotes specifications which apply over the full operating
Note 1: Absolute Maximum Ratings are those values beyond which the
life of a device may be impaired.
temperature range.
Note 2: Input bias currents are disabled when V is removed, even
CC
+
–
with common mode voltage present at IN , IN .
U
U
U
PI FU CTIO S
VCC: 5V ±10% Power Supply Input.
ensure continuity around zero inductor current. Typical out-
put is –3mV with differential input voltage (IN+ – IN–) = 0.
IN+: Sense Amplifier Positive Input. Typically connected
to inductor side of current sense resistor. Common mode
voltage range is 0V to 32V.
IN–: Sense Amplifier Negative Input. Typically connected
to load side of current sense resistor. Common mode
voltage range is 0V to 32V.
AVG: Sense Amplifier AV = –10 Output and
Transconductance Amplifier Positive Input. Used as inte-
gration node for average current control. Integration time
constant is calculated using 2.5kΩ typical output imped-
ance.
PROG: Transconductance Amplifier Negative Input. Pro-
gram node for average current delivered to load during
current mode operation. Average current delivered to load
imposes voltage differential at current sense amplifier
SENSE: Sense Amplifier AV = –1 Output. Used as level-
shiftedoutputforPWMcontrollercurrentsenseinput.The
sense output is designed to have an inherent offset to
3
LT1620/LT1621
U
U
U
PI FU CTIO S
input (across external sense resistor) equal to (VCC
–
equals (VCC – VPROG2)/20. Input voltage range is (VCC
0.15V) to (VCC – 2.5V).
–
V
PROG)/10. Input voltage range is VCC to (VCC – 1.25V).
AVG2: Sense Amplifier AV = –20 Output and Comparator
Positive Input. Used as integration node for end-of-cycle
determination flag. Integration time constant is calculated
using 5kΩ typical output impedance.
GND: Ground Reference.
MODE:ComparatorOpenCollectorOutput. Outputislogic
lowwhenmagnitudeofcurrentsenseamplifierdifferential
input voltage is less than (VCC – VPROG2)/20.
PROG2: Comparator Negative Input. Program node for
end-of-cycle determination typically used during voltage
mode operation. The comparator threshold is reached
when the current sense amplifier differential input voltage
IOUT: Transconductance Amplifier Output. In typical appli-
cation, IOUT sinks current from current-setting node on
companion PWM controller IC, facilitating current mode
loop control.
U
U
W
FUNCTIONAL BLOCK DIAGRA
5V
V
CC
INTV
CC
SENSE+
SENSE–
500Ω
SENSE
AVG
(×1 GAIN)
+
+
2.5k
–
–
(×10 GAIN)
(×20 GAIN)
PWM
CONTROLLER
5k
+
AVG2*
IN
+
CURRENT
SENSE
RESISTOR
SENSE
V
ID
AMPLIFIER
–
–
IN
+
–
I
OUT
g
I
m
TH
PROG
MODE*
END-OF-CYCLE
(ACTIVE LOW)
+
–
PROG2*
LT1620/21 • FBD
*AVAILABLE IN THE LT1620GN ONLY
GND
U
(Refer to the Functional Block Diagram)
OPERATION
Current Sense Amplifier
The first output (SENSE) is a unity gain, level-shifted repre-
sentation of the input signal (IN+ – IN–). In typical PWM/
charger type applications, this output is used to drive the
current sense amplifier of the mated PWM controller IC.
The current sense amplifier is a multiple output voltage
amplifier with an operational input common mode range
from 0V to 32V. The amplifier generates scaled output
voltages at the SENSE, AVG and AVG2 (available in
LT1620GN) pins. These output signal voltages are refer-
enced to the VCC supply by pulling signal current through
internal VCC referred resistors.
The other two outputs (AVG and AVG2) are internally
connected to a transconductance amplifier and compara-
tor, respectively. The AVG output yields a gain of 10, and
the AVG2 output provides a gain of 20. These pins are
4
LT1620/LT1621
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.
with VAVG = VPROG. In typical PWM/charger type applica-
tions, the I
current is used to servo the current control
OUT
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
chargingsystem.Thecomparatordetectswhenthecharg-
ing current has fallen to a small value (typically 20% of the
maximumchargingcurrent). Thecomparatordrivesanopen
collector output (MODE) that pulls low when the VAVG2
voltageis more positive thanVPROG2 (output current below
the programmed threshold).
Transconductance Amplifier
The transconductance amplifier converts the difference
between the current programming input voltage (VPROG
and theaveragecurrentsenseoutput(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
)
U
W U U
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.
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
This LT1620/LTC1435 battery charger is designed to yield
a 16.8V float voltage with a battery charge current of 3.2A.
TheVIN supplycanrangefrom17.3Vto28V(limitedbythe
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.
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
LT1620/LT1621
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APPLICATIONS INFORMATION
V
IN
17.3V TO 28V
+
+
C1
22µF
35V
C2
22µF
35V
R2
1.5M
C4
0.1µF
RUN
C11, 56pF
C
OSC
TG
Si4412DY
C5, 0.1µF
C13
0.033µF
X7R
C12, 0.1µF
RUN/SS
BOOST
L1
27µH
R
SENSE
D1*
0.025Ω
V
BATT
16.8V
I
SW
TH
R1
1k
C14
1nF
LTC1435
+
C3
22µF
35V
SFB
V
Li-ION
IN
D2*
C6
0.1µF
SGND
INTV
CC
V
Si4412DY
BG
OSENSE
C9, 100pF
–
SENSE
PGND
C17, 0.01µF
C7
4.7µF
+
EXTV
CC
SENSE
+
C10
100pF
5
6
4
3
+
–
IN
IN
*
D1, D2: CENTRAL
SEMICONDUCTOR CMDSH-3
V
GND
LT1620MS8
CC
C18
0.1µF
7
8
2
1
I
PROG
AVG
OUT
SENSE
R
P1
3k
C16
0.1µF
C15
0.1µF
1%
C8, 100pF
R
P2
15.75k
1%
R
F1
1.44M
0.1%
R
110k
0.1%
F2
LT1620/21 • F02
Figure 2. LT1620/LTC1435 Battery Charger
Charge Current Programming
Output Float Voltage
Output current delivered during current mode operation is
determinedthroughprogrammingthevoltageatthePROG
pin (VPROG). As mentioned above, optimum performance
is obtained with (VCC – VPROG) = 0.8V. The LT1620 is
biasedwithaprecision5VsupplyproducedbytheLTC1435,
enabling use of a simple resistor divider from VCC to
ground for a VPROG reference. Using the desired 2.5kΩ
Thevenin impedance at the PROG pin, values of RP1 = 3k
and RP2 = 15.75k are readily calculated. The PROG pin
should be decoupled to the VCC supply.
The 3.2A charger circuit is designed for a 4-cell Li-Ion
battery, or a battery float voltage of 16.8V. This voltage is
programmed through a resistor divider feedback to the
LTC1435 VOSENSE pin, referencing its 1.19V bandgap
voltage. Resistor values are determined through the rela-
tion: RF1 = (VBATT – 1.19)/(1.19/RF2). Setting RF2 = 110k
yields RF1 = 1.44M.
Other Decoupling Concerns
The application schematic shown in Figure 2 employs
severaladditionaldecouplingcapacitors. Duetotheinher-
entlynoisyenvironmentcreatedinswitchingapplications,
decoupling of sensitive nodes is prudent. As noted in the
schematic, decoupling capacitors are included on the
current programming pin (PROG) to the VCC rail and
Different values of charging current can be obtained by
changing the values of the resistors in the VPROG setting
divider to raise or lower the value of the programming
voltage, or by changing the sense resistor to an appropri-
ate value as described above.
6
LT1620/LT1621
U
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APPLICATIONS INFORMATION
between the IN+ and IN– inputs. Effective decoupling of
supply rails is also imperative in these types of circuits, as
large current transients are the norm. Power supply
decoupling should be placed as close as possible to the
ICs, and each IC should have a dedicated capacitor.
As mentioned in the previous circuit discussion, the
charging current level is set to correspond to a sense
voltage of 80mV. The circuit in Figure 3 uses a resistor
divider to create a programming voltage (VCC –VPROG2)of
0.5V. The MODE flag will therefore trip when the charging
current sense voltage has fallen to 0.5V/20 or 0.025V.
Thus, the end-of-cycle flag will trip when the charging
current has been reduced to about 30% of the maximum
value.
Design Equations
Sense resistor: RSENSE = VID/IMAX
Current limit programming voltage:
VPROG = VCC –[(10)(VID)]
Input Current Sensing Application
Voltage feedback resistors:
RF1/RF2 = (VBATT(FLOAT) – 1.19)/1.19
Monitoring the load placed on the VIN supply of a charging
system is achieved by placing a second current sense
resistor in front of the charger VIN input. This function is
useful for systems that will overstress the input supply
(wall adapter, etc.) if both battery charging and other
system functions simultaneously require high currents.
This allows use of input supply systems that are capable
of driving full-load battery charging and full-load system
requirements, but not simultaneously. If the input supply
current exceeds a predetermined value due to a combina-
tion of high battery charge current and external system
demand, the input current sense function automatically
End-of-Cycle Flag Application
Figure 3 illustrates additional connections using the
LT1620GN, including the end-of-cycle (EOC) flag feature.
The EOC threshold is used to notify the user when the
required load current has fallen to a programmed value,
usually a given percentage of maximum load.
Theend-of-cycleoutput(MODE)isanopen-collectorpull-
down; the circuit in Figure 3 uses a 10k pull-up resistor on
the MODE pin, connected to VCC.
5V
+
C1
1µF
The EOC flag threshold is determined through program-
ming VPROG2. The magnitude of this threshold corre-
sponds to 20 times the voltage across the sense amplifier
inputs.
22µF
R
P1
C2
1µF
3k
1
2
8
7
SENSE
AVG
PROG
LT1620MS8
1%
I
OUT
R
12k
1%
P2
6
5
3
4
V
GND
CC
+
–
IN
IN
R1
0.033Ω
CONNECTED AS IN FIGURE 2
LT1620GN
TO
+
SYSTEM LOAD
22µF
L1B
10µH
SENSE
AVG
MBRS340
I
OUT
V
= 12.3V
BATT
7
5
V
SW
V
IN
V
PROG
PROG2
AVG2
EE
4.7µF
24Ω
L1A
10µH
57k
+
LT1513
C1, 3.3µF
22µF
× 2
6
4
2
3
Li-ION
MODE
V
I
RUN
S/S
FB
–
IN
V
CC
6.4k
GND
FB
+
C2
3.3µF
R1
5.5k
GND
TAB
+
IN
V
C
R3
10k
R
SENSE
0.1Ω
0.22µF
8
1
R2
50k
0.1µF
X7R
END-OF-CYCLE
(ACTIVE LOW)
LT1620/21 • F03
1620/21 • F04
Figure 3. End-of-Cycle Flag Implementation with LT1620GN
Figure 4. Input Current Sensing Application
7
LT1620/LT1621
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APPLICATIONS INFORMATION
voltage VPROG. A plot of typical VPROG offset voltage vs
IN+ – IN– is pictured in Figure 5b. For example, if the
desired load current corresponds to 100mV across the
sense resistor, the typical offset, at VPROG is 7.5mV (the
absolute voltage at the PROG pin must be 7.5mV higher).
This error term should be taken into consideration when
using VID values significantly away from 80mV.
reduces battery charging current until the external load
subsides.
In Figure 4 the LT1620 is coupled with an LT1513 SEPIC
batterychargerICtocreateaninputovercurrentprotected
charger circuit.
The programming voltage (VCC – VPROG) is set to 1.0V
througharesistordivider(RP1 and RP2)fromthe5Vinput
supplytoground. Inthisconfiguration, iftheinputcurrent
drawn by the battery charger combined with the system
loadrequirementsexceedsacurrentlimitthresholdof3A,
the battery charger current will be reduced by the LT1620
such that the total input supply current is limited to 3A.
Refer to the LT1513 data sheet for additional information.
VCC – VPROG2 Programmed Voltage ≠ 1.6V
(LT1620GN Only)
The offset term described above for VPROG also affects the
VPROG2 programming voltage proportionally (times an addi-
tional factor of 2). However, VPROG2 voltage is typically set
wellbelowthezerooffsetpointof1.6V,soadjustmentforthis
term is usually required. A plot of typical VPROG2 offset
voltage vs IN+ – IN– is pictured in Figure 5c. For example,
settingtheVPROG2 voltagetocorrespondtoIN+ –IN–=15mV
typically requires an additional –50mV offset (the absolute
voltage at the PROG2 pin must be 50mV lower).
PROGRAMMING ACCURACY CONSIDERATIONS
PWM Controller Error Amp Maximum Source Current
In a typical battery charger application, the LT1620 con-
trols charge current by servoing the error amplifier output
pin of the associated PWM controller IC. Current mode
control is achieved when the LT1620 sinks all of the
currentavailablefromtheerroramplifier.SincetheLT1620
has finite transconductance, the voltage required to gen-
erate its necessary output current translates to input
offset error. The LT1620 is designed for a typical IOUT sink
current of 130µA to help reduce this term. Knowing the
current source capability of the associated PWM control-
ler in a given application will enable adjustment of the
required programming voltage to accommodate the de-
sired charge current. A plot of typical VPROG voltage offset
vs PWM source capability is shown in Figure 5a. For
example, the LTC1435 has a current source capability of
about 75µA. This translates to about –15mV of induced
programming offset at VPROG (the absolute voltage at the
PROG pin must be 15mV lower).
Sense Amplifier Input Common Mode < (VCC – 0.5V)
The LT1620 sense amplifier has additional input offset
tolerance when the inputs are pulled significantly below
the VCC supply. The amplifier can induce additional input
referred offset of up to 11mV when the inputs are at 0V
common-mode.Thisadditionaloffsettermreducesroughly
linearly to zero when VCM is about VCC – 0.5V. In typical
applications, this offset increases the charge current tol-
erance for “cold start” conditions until VBAT moves away
from ground. The resulting output current shift is generally
negative; however, this offset is not precisely controlled.
Precision operation should not be attempted with sense
amplifier common mode inputs below VCC – 0.5V. Input
referred offset tolerance vs VCM is shown in Figure 5d.
VCC ≠ 5V
The LT1620 sense amplifier induces a small additional
offset when VCC moves away from 5V. This offset follows
a linear characteristic and amounts to about ±0.33mV
(input-referred) over the recommended operating range
of VCC, centered at 5V. This offset is translated to the AVG
and AVG2 outputs (times factors of 10 and 20), and thus
to the programming voltages. A plot of programming
offsets vs VCC is shown in Figure 5e.
VCC – VPROG Programmed Voltage ≠ 0.8V
The LT1620 sense amplifier circuit has an inherent input
referred 3mV offset when IN+ – IN– = 0V to insure closed-
loop operation during light load conditions. This offset vs
input voltage has a linear characteristic, crossing 0V as
IN+ – IN– = 80mV. The offset is translated to the AVG
output(timesafactorof10),andthustotheprogramming
8
LT1620/LT1621
U
W U U
APPLICATIONS INFORMATION
40
20
10
V
V
V
= 5V
= 80mV
= 16.8V
V
V
I
= 5V
CC
ID
CM
CC
CM
30
20
= 16.8V
= 130µA
OUT
0
10
0
–10
–20
–30
–40
–10
–20
–30
–40
50
100
200
0
250
150
80
120 140
0
20
40
+
60
100
–
I
SINK CURRENT (µA)
IN – IN (V ) INPUT (mV)
OUT
ID
LT1620/21 • F05a
LT1620/21 • F05b
Figure 5a. Typical Setpoint Voltage (VPROG) Changes Slightly
Depending Upon the Amount of Current Sinked by the IOUT Pin
Figure 5b. Typical Setpoint Voltage (VPROG) Changes Slightly
Depending Upon the Programmed Differential Input Voltage (VID)
40
±14
V
V
I
= 5V
V
V
I
= 5V
CC
ID
CC
CM
= 80mV
= 130µA
= 16.8V
= 130µA
±12
±10
±8
±6
±4
±2
0
20
0
OUT
OUT
–20
–40
–60
–80
4
36
80
120 140
0
1
–
2
3
5
0
20
40
+
60
–
100
+
IN , IN COMMON MODE VOLTAGE (V ) (V)
CM
IN – IN (V ) INPUT (mV)
ID
LT1620/21 • F05d
LT1620/21 • F05c
Figure 5c. Typical Comparator Threshold Voltage (VPROG2
)
Figure 5d. Sense Amplifier Input Offset Tolerence Degrades for
Input Common Mode Voltage (VCM) Below (VCC – 0.5V). This
Affects the SENSE, AVG and AVG2 Amplifier Outputs
Changes Slightly Depending Upon the Programmed Differential
Input Voltage (VID)
10
V
V
= 80mV
ID
= 16.8mV
CM
OUT
I
= 130µA
5
V
PROG2
V
PROG
0
–5
–10
5.00
(V)
5.25
4.50
5.50
4.75
V
CC
LT1620/21 • F05e
Figure 5e. Typical Setpoint Voltages for VPROG and VPROG2
Change Slightly Depending Upon the Supply Voltage (VCC
)
9
LT1620/LT1621
U
TYPICAL APPLICATIONS
Programmable Constant Current Source
D45VH10
0.1Ω
6V
TO 28V
I
OUT
0A TO 1A
0.1µF
470Ω
LT1121CS8-5
8
1
IN
OUT
+
0.1µF
SHDN GND
1µF
10k
1%
0.1µF
5
3
18k
0.1µF
1
2
8
7
SENSE
AVG
SHUTDOWN
I
PROG
VN2222LM
OUT
LT1620MS8
3
4
6
5
V
2N3904
GND
CC
I
PROG
R
PROG
22Ω
+IN
–IN
I
= (I
PROG
)(10,000)
OUT
PROG
R
= 40k FOR 1A OUTPUT
LT1620/21 • TA01
High Efficiency Buck Constant Current Source
50µH
CTX50-4
Si9405
0.05Ω
I
6V TO
15V
OUT
0A TO 1A
22µF
25V
TPS
+
25V
TPS
+
4.7k
10k
22µF
MBRS130T3
2N4401
2N4403
5V
0.04µ7F
10k
1%
0.1µF
820Ω
20k
0.1µF
10k
1
3
16
14
SENSE
AVG
2N7002
I
PROG
OUT
LT1620GN
1µF
13
PROG2
4.7k
5
GND
12
11
9
AVG2
6
8
I
R
PROG
PROG
MODE
–IN
V
CC
47k
+IN
2N7002
I
= (I
PROG
)(20,000)
OUT
PROG
33k
R
= 90k FOR 1A OUTPUT
LT1620/21 • TA04
10
LT1620/LT1621
U
Dimensions in inches (millimeters) unless otherwise noted.
PACKAGE DESCRIPTIO
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
0.229 – 0.244
(5.817 – 6.198)
0.015 ± 0.004
(0.38 ± 0.10)
0.150 – 0.157**
(3.810 – 3.988)
× 45° 0.053 – 0.069
0.004 – 0.009
(0.102 – 0.249)
(1.351 – 1.748)
0.0075 – 0.0098
(0.191 – 0.249)
0° – 8° TYP
0.016 – 0.050
(0.406 – 1.270)
0.008 – 0.012
(0.203 – 0.305)
0.025
(0.635)
BSC
1
2
3
4
5
6
7
8
*
DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
GN16 (SSOP) 0895
** DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
MS8 Package
8-Lead MSOP
(LTC DWG # 05-08-1660)
0.118 ± 0.004*
(3.00 ± 0.10)
8
7
6
5
0.040 ± 0.006
(1.02 ± 0.15)
0.006 ± 0.004
(0.15 ± 0.10)
0.007
(0.18)
0° – 6° TYP
0.118 ± 0.004**
(3.00 ± 0.10)
0.192 ± 0.004
(4.88 ± 0.10)
SEATING
PLANE
0.021 ± 0.004
(0.53 ± 0.01)
0.012
(0.30)
0.025
(0.65)
TYP
1
2
3
4
*
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.
MSOP08 0596
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
S8 Package
8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
0.189 – 0.197*
(4.801 – 5.004)
7
5
8
6
0.228 – 0.244
(5.791 – 6.197)
0.010 – 0.020
(0.254 – 0.508)
× 45°
0.053 – 0.069
(1.346 – 1.752)
0.004 – 0.010
(0.101 – 0.254)
0.150 – 0.157**
(3.810 – 3.988)
0.008 – 0.010
(0.203 – 0.254)
0°– 8° TYP
0.016 – 0.050
0.406 – 1.270
0.050
(1.270)
TYP
0.014 – 0.019
(0.355 – 0.483)
1
3
4
2
*DIMENSION DOES NOT INCLUDE MOLD FLASH. MOLD FLASH
SHALL NOT EXCEED 0.006" (0.152mm) PER SIDE
SO8 0996
**DIMENSION DOES NOT INCLUDE INTERLEAD FLASH. INTERLEAD
FLASH SHALL NOT EXCEED 0.010" (0.254mm) PER SIDE
InformationfurnishedbyLinearTechnologyCorporationisbelievedtobeaccurateandreliable.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
LT1620/LT1621
TYPICAL APPLICATION
U
Electronic Circuit Breaker
Si9434DY
0.033Ω
5V AT 1A
PROTECTED
5V
0.1µF
1k
FAULT
C
DELAY
100Ω
1N4148
1
2
8
7
33k
SENSE
AVG
100k
I
PROG
2N3904
OUT
LT1620MS8
4.7k
3
4
6
5
33k
V
GND
CC
+IN
–IN
2N3904
TYPICAL DC TRIP AT 1.6A
3A FAULT TRIPS
LT1620/21 • TA03
IN 2ms WITH C
= 1.0µF
DELAY
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
®
LTC 1435
High Efficiency Low Noise Synchronous Step-Down
Switching Regulator
16-Pin Narrow SO and SSOP, V ≤ 36V, Programmable
Constant Frequency
IN
LTC1436/LTC1436-PPL/ High Efficiency Low Noise Synchronous Step-Down
Full-Featured Single Controller, V ≤ 36V, Programmable
Constant Frequency
IN
LTC1437
Switching Regulator Controllers
LTC1438/LTC1439
Dual High Efficiency Low Noise Synchronous Step-Down Full-Featured Dual Controllers, V ≤ 36V, Programmable
IN
Switching Regulators
Constant Frequency
LT1510
LT1511
1.5A Constant-Current/Constant-Voltage Battery Charger Step-Down Charger for Li-Ion, NiCd and NiMH
3.0A Constant-Current/Constant-Voltage Battery Charger Step-Down Charger that Allows Charging During Computer
with Input Current Limiting
Operation and Prevents Wall-Adapter Overload
LT1512
SEPIC Constant-Current/Constant-Voltage Battery Charger Step-Up/Step-Down Charger for up to 1A Charging Current
SEPIC Constant-Current/Constant-Voltage Battery Charger Step-Up/Step-Down Charger for up to 2A Charging Current
LT1513
LTC1538-AUX
Dual High Efficiency Low Noise Synchronous Step-Down 5V Standby in Shutdown, V ≤ 36V, Programmable
IN
Switching Regulator
Constant Frequency
LTC1539
Dual High Efficiency Low Noise Synchronous Step-Down 5V Standby in Shutdown, V ≤ 36V, Programmable
IN
Switching Regulator
Constant Frequency
16201f LT/GP 0197 7K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1996
12 Linear Technology Corporation
●
1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408)432-1900
●
●
FAX: (408) 434-0507 TELEX: 499-3977 www.linear-tech.com
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