LT1620/LT1621
Rail-to-Rail Current
Sense Amplifier
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DESCRIPTIO
FEATURES
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■
■
■
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Accurate Output Current Programming
Usable in Charging Applications Up to 32V Output
Programmable Load Current Monitor for End-ofCharging-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
Can be Used for NiCd, NiMH, Lead-Acid and LithiumIon Battery Charging
Greater than 96% Efficiency Possible in Charger
Applications
High Output Currents Possible: > 10A
Easily Obtained
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APPLICATI
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S
High Current Battery Chargers
High Output Voltage DC/DC Converters
Constant Current Sources
Overcurrent Fault Protectors
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 restriction 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 programmable 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.
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TYPICAL APPLICATI
(VBATT + 0.5V) TO 32V
VIN
LTC1435
SYNCHRONOUS
BUCK
REGULATOR
0.1µF
6
VCC
1
8
SENSE
AVG
2
7
IOUT
PROG
LT1620MS8
3
GND
4
5
IN –
IN +
Efficiency
100
VBATT
27µH
VIN = 24V
IBATT TO 4A
SW
SENSE –
INTVCC
VIN
22µF
35V
×2
0.025Ω
1.43M
0.1%
FB
0.1µF
110k
0.1%
3k
1%
VBATT = 16V
95
VBATT = 12V
+
22µF
35V
EFFICIENCY (%)
ITH
+
90
VBATT = 6V
85
80
15.75k
1%
75
LT1620/21 • F01
SIMPLIFIED SCHEMATIC. SEE FIGURE 2 FOR COMPLETE SCHEMATIC
Figure 1. Low Dropout, High Current Li-Ion Battery Charger
0
1
3
4
2
BATTERY CHARGE CURRENT (A)
5
1620/21 • TA02
1
LT1620/LT1621
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ABSOLUTE
RATI GS (Referenced to Ground) (Note 1)
Power Supply Voltage: VCC ..........................– 0.3V to 7V
Programming Voltage:
PROG, PROG2 ............ – 0.3V to VCC + 0.3V (7V Max)
IOUT, SENSE, AVG, AVG2,
MODE Voltage ................ – 0.3V to VCC + 0.3V (7V Max)
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
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PACKAGE/ORDER I FOR ATIO
TOP VIEW
TOP VIEW
TOP VIEW
16 AVG
SENSE 1
PROG A 1
16 VCC A
AVG A 2
15 IN + A
SENSE A 3
14 IN – A
SENSE 1
8
AVG
IOUT 2
7
PROG
GND 3
6
VCC
IOUT 3
14 PROG
IN – 4
5
IN +
NC 4
13 PROG2
IOUT A 4
13 GND A
12 AVG2
GND B 5
12 IOUT B
15 NC
NC 2
GND 5
MS8 PACKAGE
S8 PACKAGE
8-LEAD PLASTIC MSOP
8-LEAD PLASTIC SO
θJA = 250°C/W (MS)
θJA = 120°C/W (S)
MODE 6
NC 7
IN –
ORDER PART NUMBER
LT1620CS8
LT1620IS8
LT1620CMS8
11 VCC
IN – B
6
11 SENSE B
10 NC
IN + B
7
10 AVG B
9
8
9
VCC B 8
IN +
PROG B
GN PACKAGE
16-LEAD PLASTIC SSOP
θJA = 149°C/W
GN PACKAGE
16-LEAD PLASTIC SSOP
ORDER PART NUMBER
ORDER PART NUMBER
LT1620CGN
LT1620IGN
LT1621CGN
LT1621IGN
MS8 PART MARKING
BC
θJA = 149°C/W
Consult factory for Military grade parts.
ELECTRICAL CHARACTERISTICS
VIN+ = 16.8V, VCC = 5V, VIOUT = 2V, TA = 25°C unless otherwise noted.
SYMBOL PARAMETER
Supply
VCC
5V Supply Voltage
ICC
DC Active Supply Current
LT1620GN
DC Active Supply Current
LT1620S8, LT1620MS8, 1/2 LT1621GN
DC Active Supply Current
LT1620S8, LT1620MS8, 1/2 LT1621GN
Current Sense Amplifier
VCM
Input Common Mode Range
Differential Input Voltage Range
VID
(IN+ – IN –)
VOSSENSE Input Offset - Measured at ×1 Output
(VSENSE)
2
CONDITIONS
●
SENSE = AVG = PROG = PROG2 = VCC
4.5V ≤ VCC ≤ 5.5V, IN+ – IN – = 100mV
SENSE = AVG = PROG = VCC
4.5V ≤ VCC ≤ 5.5V, IN+ – IN – = 100mV
SENSE = AVG = PROG = VCC
4.5V ≤ VCC ≤ 5.5V, IN+ – IN – = 0mV
MIN
TYP
MAX
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
●
2.3
●
1.3
●
UNITS
0V ≤ VCM ≤ 32V
●
0
0
32
125
V
mV
VCC ≤ VCM ≤ 32V
VID = 80mV
●
–5
–6
5
6
mV
mV
●
LT1620/LT1621
ELECTRICAL CHARACTERISTICS
IN+ = 16.8V, VCC = 5V, VIOUT = 2V, TA = 25°C unless otherwise noted.
SYMBOL PARAMETER
Current Sense Amplifier
Input Offset - Measured at ×10 Output
VOSAVG
(VAVG)
Input Offset - Measured at × 20 Output
(VAVG2)
VSENSE
No-Load Output Offset
+
–
IB(IN , IN ) Input Bias Current (Sink)
VOSAVG2
CONDITIONS
MIN
VCC ≤ VCM ≤ 32V
35mV ≤ VID ≤ 125mV
VCM = 0V, VID = 80mV
VCC ≤ VCM ≤ 32V
0V ≤ VID ≤ 35mV
0V ≤ VCM ≤ 32V, VID = 0V, Referenced to VCC
VCC ≤ VCM ≤ 32V (Note 2)
●
●
●
●
●
Input Bias Current (Source)
–3
–4
– 10
–3
–4
– 0.1
200
185
VCM = 0V (Note 2)
TYP
3
4
15
3
4
–3
270
4.0
●
Transconductance Amplifier
Amplifier Transconductance
gm
●
AV
VOLIOUT
Amplifier Voltage Gain
IOUT Saturation Limit (Sink)
VPROG
IBPROG
VOSPROG
PROG Input Range
Input Bias Current
Input Offset Voltage
(VAVG – VPROG)
End-of-Cycle Comparator
VPROG2
PROG2 Input Range
VHYST
Input Hysteresis
IBPROG2 Input Bias Current
VOLMODE Output Logic Low Output (Sink)
1V ≤ VIOUT ≤ 3V
IIOUT = 50µA
IIOUT = 200µA
IIOUT = 1mA
●
●
●
●
VCC – 1.25
●
–7
–8
●
VCC – 2.5
Measured at PROG Pin
IIOUT = 130µA
Measured at AVG2 Pin
Measured at PROG2 Pin
IMODE = 0.5mA
IMODE = 10mA
The ● denotes specifications which apply over the full operating
temperature range.
3000
2200
60
MAX
3500
80
0.05
0.10
0.35
400
430
5.25
5.50
4000
4800
0.15
0.30
0.65
VCC
20
●
●
7
8
VCC – 0.15
15
20
0.1
0.5
0.5
1.2
UNITS
mV
mV
mV
mV
mV
mV
µA
µA
mA
mA
µmho
µmho
dB
V
V
V
V
nA
mV
mV
V
mV
nA
V
V
Note 1: Absolute Maximum Ratings are those values beyond which the
life of a device may be impaired.
Note 2: Input bias currents are disabled when VCC is removed, even
with common mode voltage present at IN+, IN–.
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VCC: 5V ±10% Power Supply Input.
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.
SENSE: Sense Amplifier AV = – 1 Output. Used as levelshifted output for PWM controller current sense input. The
sense output is designed to have an inherent offset to
ensure continuity around zero inductor current. Typical output is –3mV with differential input voltage (IN+ – IN–) = 0.
AVG: Sense Amplifier A V = –10 Output and
Transconductance Amplifier Positive Input. Used as integration node for average current control. Integration time
constant is calculated using 2.5kΩ typical output impedance.
PROG: Transconductance Amplifier Negative Input. Program node for average current delivered to load during
current mode operation. Average current delivered to load
imposes voltage differential at current sense amplifier
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LT1620/LT1621
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PI FU CTIO S
input (across external sense resistor) equal to (VCC –
VPROG)/10. Input voltage range is VCC to (VCC – 1.25V).
equals (VCC – VPROG2)/20. Input voltage range is (VCC –
0.15V) to (VCC – 2.5V).
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.
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 application, IOUT sinks current from current-setting node on
companion PWM controller IC, facilitating current mode
loop control.
MODE: Comparator Open Collector Output. Output is logic
low when magnitude of current sense amplifier differential
input voltage is less than (VCC – VPROG2)/20.
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FUNCTIONAL BLOCK DIAGRA
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5V
VCC
500Ω
+
–
+
–
(×1 GAIN) SENSE
2.5k
(×10 GAIN)
5k
IN+
CURRENT
SENSE
RESISTOR
VID
IN–
+
SENSE
AMPLIFIER
PROG
IOUT
ITH
–
+
PROG2*
MODE*
END-OF-CYCLE
(ACTIVE LOW)
–
GND
LT1620/21 • FBD
(Refer to the Functional Block Diagram)
Current Sense Amplifier
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 referenced to the VCC supply by pulling signal current through
internal VCC referred resistors.
4
PWM
CONTROLLER
+
–
*AVAILABLE IN THE LT1620GN ONLY
AVG
(×20 GAIN) AVG2*
gm
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OPERATION
INTVCC
SENSE +
SENSE –
The first output (SENSE) is a unity gain, level-shifted representation 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 other two outputs (AVG and AVG2) are internally
connected to a transconductance amplifier and comparator, respectively. The AVG output yields a gain of 10, and
the AVG2 output provides a gain of 20. These pins are
LT1620/LT1621
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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
with VAVG = VPROG. In typical PWM/charger type applications, 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 charging 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).
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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 regulator 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 functionality, 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 programmed 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 programming 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 resistor 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
LT1620/LT1621
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APPLICATIONS INFORMATION
+
R2
1.5M
C4
0.1µF
RUN
C11, 56pF
C13
0.033µF
X7R
C12, 0.1µF
COSC
TG
RUN/SS
BOOST
R1
1k
SFB
C9, 100pF
5
6
C18
0.1µF
7
8
RP1
3k
1%
C16
0.1µF
IN+
IN–
VCC
GND
LT1620MS8
IOUT
PROG
AVG
SENSE
4
C2
22µF
35V
VIN
17.3V TO 28V
RSENSE
0.025Ω
VBATT
16.8V
SW
LTC1435
SGND
C17, 0.01µF
+
Si4412DY
L1
27µH
D1*
ITH
C14
1nF
C5, 0.1µF
C1
22µF
35V
VIN
+
D2*
C6
0.1µF
INTVCC
VOSENSE
BG
SENSE –
PGND
SENSE +
EXTVCC
C3
22µF
35V
Li-ION
Si4412DY
+
C7
4.7µF
C10
100pF
* D1, D2: CENTRAL
SEMICONDUCTOR CMDSH-3
3
2
1
C15
0.1µF
C8, 100pF
RP2
15.75k
1%
RF2
110k
0.1%
RF1
1.44M
0.1%
LT1620/21 • F02
Figure 2. LT1620/LTC1435 Battery Charger
Charge Current Programming
Output Float Voltage
Output current delivered during current mode operation is
determined through programming the voltage at the PROG
pin (VPROG). As mentioned above, optimum performance
is obtained with (VCC – VPROG) = 0.8V. The LT1620 is
biased with a precision 5V supply produced by the LTC1435,
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 relation: RF1 = (VBATT – 1.19)/(1.19/RF2). Setting RF2 = 110k
yields RF1 = 1.44M.
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 appropriate value as described above.
6
Other Decoupling Concerns
The application schematic shown in Figure 2 employs
several additional decoupling capacitors. Due to the inherently noisy environment created in switching applications,
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
LT1620/LT1621
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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.
Design Equations
Sense resistor: RSENSE = VID /IMAX
Current limit programming voltage:
VPROG = VCC – [(10)(VID)]
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.
Input Current Sensing Application
Voltage feedback resistors:
RF1/RF2 = (VBATT(FLOAT) – 1.19)/1.19
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.
The end-of-cycle output (MODE) is an open-collector pulldown; the circuit in Figure 3 uses a 10k pull-up resistor on
the MODE pin, connected to VCC.
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 combination of high battery charge current and external system
demand, the input current sense function automatically
5V
The EOC flag threshold is determined through programming VPROG2. The magnitude of this threshold corresponds to 20 times the voltage across the sense amplifier
inputs.
+
C1
1µF
22µF
1
2
SENSE
AVG
7
PROG
LT1620MS8
6
3
VCC
GND
4
IOUT
IN+
IN–
22µF
L1B
10µH
AVG
MBRS340
7
PROG
4.7µF
+
RUN
+
IN+
R3
10k
6
4
C2
3.3µF
R1
5.5k
R2
50k
END-OF-CYCLE
(ACTIVE LOW)
LT1620/21 • F03
Figure 3. End-of-Cycle Flag Implementation with LT1620GN
S/S
VFB
GND
GND
TAB
IFB
8
VBATT = 12.3V
5
LT1513
C1, 3.3µF
AVG2
VCC
VSW
VIN
PROG2
IN–
TO
SYSTEM LOAD
+
IOUT
MODE
RP2
12k
1%
R1
0.033Ω
LT1620GN
VEE
C2
1µF
5
CONNECTED AS IN FIGURE 2
SENSE
RP1
3k
1%
8
L1A
10µH
57k
+
2
3
22µF
×2
Li-ION
24Ω
6.4k
VC
0.22µF
1
RSENSE
0.1Ω
0.1µF
X7R
1620/21 • F04
Figure 4. Input Current Sensing Application
7
LT1620/LT1621
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APPLICATIONS INFORMATION
reduces battery charging current until the external load
subsides.
In Figure 4 the LT1620 is coupled with an LT1513 SEPIC
battery charger IC to create an input overcurrent protected
charger circuit.
The programming voltage (VCC – VPROG) is set to 1.0V
through a resistor divider (RP1 and RP2) from the 5V input
supply to ground. In this configuration, if the input current
drawn by the battery charger combined with the system
load requirements exceeds a current limit threshold of 3A,
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.
PROGRAMMING ACCURACY CONSIDERATIONS
PWM Controller Error Amp Maximum Source Current
In a typical battery charger application, the LT1620 controls 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
current available from the error amplifier. Since the LT1620
has finite transconductance, the voltage required to generate 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 controller in a given application will enable adjustment of the
required programming voltage to accommodate the desired 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).
VCC – VPROG Programmed Voltage ≠ 0.8V
The LT1620 sense amplifier circuit has an inherent input
referred 3mV offset when IN+ – IN– = 0V to insure closedloop 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 (times a factor of 10), and thus to the programming
8
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.
VCC – VPROG2 Programmed Voltage ≠ 1.6V
(LT1620GN Only)
The offset term described above for VPROG also affects the
VPROG2 programming voltage proportionally (times an additional factor of 2). However, VPROG2 voltage is typically set
well below the zero offset point of 1.6V, so adjustment for this
term is usually required. A plot of typical VPROG2 offset
voltage vs IN+ – IN– is pictured in Figure 5c. For example,
setting the VPROG2 voltage to correspond to IN+ – IN– = 15mV
typically requires an additional –50mV offset (the absolute
voltage at the PROG2 pin must be 50mV 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. This additional offset term reduces roughly
linearly to zero when VCM is about VCC – 0.5V. In typical
applications, this offset increases the charge current tolerance 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.
LT1620/LT1621
U
W
U
U
APPLICATIONS INFORMATION
40
20
VCC = 5V
VID = 80mV
VCM = 16.8V
20
VCC = 5V
VCM = 16.8V
IOUT = 130µA
10
VPROG OFFSET (mV)
VPROG OFFSET (mV)
30
10
0
–10
0
–10
–20
–20
–30
–30
–40
50
0
100
200
150
IOUT SINK CURRENT (µA)
–40
250
0
20
80 100 120
60
40
IN+ – IN– (VID) INPUT (mV)
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)
VPROG2 OFFSET (mV)
ADDITIONAL INPUT REFERRED OFFSET (mV)
40
VCC = 5V
VCM = 16.8V
IOUT = 130µA
20
0
–20
–40
–60
–80
0
20
80 100 120
60
40
IN+ – IN– (VID) INPUT (mV)
140
±14
VCC = 5V
VID = 80mV
IOUT = 130µA
±12
±10
±8
±6
±4
±2
0
0
140
4
36
3
5
1
2
IN+, IN– COMMON MODE VOLTAGE (VCM) (V)
LT1620/21 • F05d
LT1620/21 • F05c
Figure 5c. Typical Comparator Threshold Voltage (VPROG2)
Changes Slightly Depending Upon the Programmed Differential
Input Voltage (VID)
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
PROGRAMMING OFFSET (mV)
10
VID = 80mV
VCM = 16.8mV
IOUT = 130µA
5
VPROG2
0
VPROG
–5
–10
4.50
4.75
5.00
5.25
5.50
VCC (V)
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
6V
TO 28V
0.1Ω
IOUT
0A TO 1A
0.1µF
470Ω
LT1121CS8-5
8
IN
0.1µF
OUT
SHDN
5
1
GND
3
SHUTDOWN
+
0.1µF
1µF
18k
1
SENSE
AVG
7
PROG
LT1620MS8
3
6
VCC
GND
2
VN2222LM
2N3904
22Ω
4
10k
1%
0.1µF
8
IOUT
+IN
–IN
IPROG
RPROG
5
IOUT = (IPROG)(10,000)
RPROG = 40k FOR 1A OUTPUT
LT1620/21 • TA01
High Efficiency Buck Constant Current Source
6V TO
15V
50µH
CTX50-4
Si9405
+
22µF
25V
TPS
0.05Ω
+
4.7k
MBRS130T3
2N4401
IOUT
0A TO 1A
22µF
25V
TPS
10k
2N4403
5V
0.1µF
820Ω
10k
2N7002
0.047 µF
1
3
4.7k
SENSE
IOUT
1µF
5
6
8
AVG
20k
0.1µF
10k
1%
14
PROG
LT1620GN
13
PROG2
GND
AVG2
MODE
–IN
16
VCC
+IN
12
IPROG
11
9
RPROG
47k
2N7002
33k
IOUT = (IPROG)(20,000)
RPROG = 90k FOR 1A OUTPUT
LT1620/21 • TA04
10
LT1620/LT1621
U
PACKAGE DESCRIPTIO
Dimensions in inches (millimeters) unless otherwise noted.
GN Package
16-Lead Plastic SSOP (Narrow 0.150)
0.189 – 0.196*
(4.801 – 4.978)
(LTC DWG # 05-08-1641)
16 15 14 13 12 11 10 9
0.015 ± 0.004
× 45°
(0.38 ± 0.10)
0.0075 – 0.0098
(0.191 – 0.249)
0.229 – 0.244
(5.817 – 6.198)
0.053 – 0.069
(1.351 – 1.748)
0.150 – 0.157**
(3.810 – 3.988)
0.004 – 0.009
(0.102 – 0.249)
0° – 8° TYP
0.016 – 0.050
(0.406 – 1.270)
0.025
(0.635)
BSC
0.008 – 0.012
(0.203 – 0.305)
1
2 3
5 6
4
7
* 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
8
GN16 (SSOP) 0895
MS8 Package
8-Lead MSOP
(LTC DWG # 05-08-1660)
0.118 ± 0.004*
(3.00 ± 0.10)
8
0.040 ± 0.006
(1.02 ± 0.15)
0.007
(0.18)
0° – 6° TYP
SEATING
PLANE
0.021 ± 0.004
(0.53 ± 0.01)
7 6
5
0.006 ± 0.004
(0.15 ± 0.10)
0.118 ± 0.004**
(3.00 ± 0.10)
0.192 ± 0.004
(4.88 ± 0.10)
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
1
2 3
4
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
0.010 – 0.020
× 45°
(0.254 – 0.508)
0.008 – 0.010
(0.203 – 0.254)
0.053 – 0.069
(1.346 – 1.752)
0°– 8° TYP
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
7
6
5
0.228 – 0.244
(5.791 – 6.197)
0.150 – 0.157**
(3.810 – 3.988)
0.004 – 0.010
(0.101 – 0.254)
0.050
(1.270)
TYP
1
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.
2
3
4
SO8 0996
11
LT1620/LT1621
U
TYPICAL APPLICATION
Electronic Circuit Breaker
Si9434DY
0.033Ω
5V AT 1A
PROTECTED
5V
0.1µF
1k
FAULT
CDELAY
100Ω
33k
2N3904
1
2
SENSE
AVG
1N4148
8
7
PROG
LT1620MS8
6
3
VCC
GND
4
100k
IOUT
–IN
+IN
4.7k
33k
5
TYPICAL DC TRIP AT 1.6A
3A FAULT TRIPS
IN 2ms WITH CDELAY = 1.0µF
2N3904
LT1620/21 • TA03
RELATED PARTS
PART NUMBER
DESCRIPTION
COMMENTS
LTC®1435
High Efficiency Low Noise Synchronous Step-Down
Switching Regulator
16-Pin Narrow SO and SSOP, VIN ≤ 36V, Programmable
Constant Frequency
LTC1436/LTC1436-PPL/ High Efficiency Low Noise Synchronous Step-Down
LTC1437
Switching Regulator Controllers
Full-Featured Single Controller, VIN ≤ 36V, Programmable
Constant Frequency
LTC1438/LTC1439
Dual High Efficiency Low Noise Synchronous Step-Down
Switching Regulators
Full-Featured Dual Controllers, VIN ≤ 36V, Programmable
Constant Frequency
LT1510
1.5A Constant-Current/Constant-Voltage Battery Charger
Step-Down Charger for Li-Ion, NiCd and NiMH
LT1511
3.0A Constant-Current/Constant-Voltage Battery Charger
with Input Current Limiting
Step-Down Charger that Allows Charging During Computer
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
LT1513
SEPIC Constant-Current/Constant-Voltage Battery Charger Step-Up/Step-Down Charger for up to 2A Charging Current
LTC1538-AUX
Dual High Efficiency Low Noise Synchronous Step-Down
Switching Regulator
5V Standby in Shutdown, VIN ≤ 36V, Programmable
Constant Frequency
LTC1539
Dual High Efficiency Low Noise Synchronous Step-Down
Switching Regulator
5V Standby in Shutdown, VIN ≤ 36V, Programmable
Constant Frequency
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
16201f LT/GP 0197 7K • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1996
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