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LT1620/LT1621 Rail-to-Rail Current Sense Amplifier
FEATURES
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DESCRIPTIO
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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
The LT (R)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.
APPLICATI
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High Current Battery Chargers High Output Voltage DC/DC Converters Constant Current Sources Overcurrent Fault Protectors
TYPICAL APPLICATI
(VBATT + 0.5V) TO 32V VIN LTC1435 SYNCHRONOUS BUCK REGULATOR ITH SENSE - INTVCC 0.1F 6 VCC 1 8 SENSE AVG 2 7 IOUT PROG LT1620MS8 3 GND 4 5 IN - IN + 0.1F 3k 1% 15.75k 1% FB SW 27H 0.025
+
VIN
22F 35V x2
IBATT TO 4A VBATT 1.43M 0.1%
22F 35V
EFFICIENCY (%)
+
110k 0.1%
LT1620/21 * F01
SIMPLIFIED SCHEMATIC. SEE FIGURE 2 FOR COMPLETE SCHEMATIC
Figure 1. Low Dropout, High Current Li-Ion Battery Charger
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Efficiency
100 VIN = 24V VBATT = 16V 95 VBATT = 12V 90 VBATT = 6V 85 80 75 0 1 3 4 2 BATTERY CHARGE CURRENT (A) 5
1620/21 * TA02
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LT1620/LT1621 ABSOLUTE AXI U RATI GS (Referenced to Ground) (Note 1)
Sense Amplifier Input Common Mode .......- 0.3V to 36V Operating Ambient Temperature Range Commercial ............................................ 0C to 70C Industrial ............................................ - 40C to 85C Storage Temperature Range ................ - 65C to 150C Lead Temperature (Soldering, 10 sec)................. 300C 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)
PACKAGE/ORDER I FOR ATIO
TOP VIEW SENSE 1 IOUT 2 GND 3 IN - 4 8 7 6 5 AVG PROG VCC IN +
SENSE 1 NC 2 IOUT 3 NC 4 GND 5
MS8 PACKAGE S8 PACKAGE 8-LEAD PLASTIC MSOP 8-LEAD PLASTIC SO JA = 250C/W (MS) JA = 120C/W (S)
MODE 6 NC 7 IN - 8
ORDER PART NUMBER LT1620CS8 LT1620IS8 LT1620CMS8 MS8 PART MARKING BC
Consult factory for Military grade parts.
GN PACKAGE 16-LEAD PLASTIC SSOP JA = 149C/W
ORDER PART NUMBER LT1620CGN LT1620IGN
ELECTRICAL CHARACTERISTICS
VIN+ = 16.8V, VCC = 5V, VIOUT = 2V, TA = 25C 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 x1 Output (VSENSE) CONDITIONS
q
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
0V VCM 32V VCC VCM 32V VID = 80mV
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TOP VIEW 16 AVG 15 NC 14 PROG 13 PROG2 12 AVG2 11 VCC 10 NC 9 IN +
TOP VIEW PROG A 1 AVG A 2 SENSE A 3 IOUT A 4 GND B 5 IN - B IN + B 6 7 16 VCC A 15 IN + A 14 IN - A 13 GND A 12 IOUT B 11 SENSE B 10 AVG B 9 PROG B
VCC B 8
GN PACKAGE 16-LEAD PLASTIC SSOP
JA = 149C/W
ORDER PART NUMBER LT1621CGN LT1621IGN
MIN 4.5
TYP 5.0 2.8 2.3
MAX 5.5 3.8 4.0 3.3 3.7 1.9 2.1 32 125 5 6
UNITS V mA mA mA mA mA mA V mV mV mV
q q
1.3
q q q
0 0 -5 -6
q
LT1620/LT1621
IN+ = 16.8V, VCC = 5V, VIOUT = 2V, TA = 25C unless otherwise noted.
SYMBOL PARAMETER Current Sense Amplifier Input Offset - Measured at x10 Output VOSAVG (VAVG) Input Offset - Measured at x 20 Output (VAVG2) VSENSE No-Load Output Offset + - IB(IN , IN ) Input Bias Current (Sink) VOSAVG2 Input Bias Current (Source) Transconductance Amplifier Amplifier Transconductance gm
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ELECTRICAL CHARACTERISTICS
CONDITIONS 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) VCM = 0V (Note 2)
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MIN -3 -4 - 10 -3 -4 - 0.1 200 185
TYP
MAX 3 4 15 3 4
UNITS mV mV mV mV mV mV A A mA mA mho mho dB V V V V nA mV mV V mV nA V V
q q q q q
-3 270 4.0
400 430 5.25 5.50 4000 4800 0.15 0.30 0.65 VCC 7 8 VCC - 0.15
AV VOLIOUT
Amplifier Voltage Gain IOUT Saturation Limit (Sink)
1V VIOUT 3V IIOUT = 50A IIOUT = 200A IIOUT = 1mA Measured at PROG Pin IIOUT = 130A
3000 2200 60
3500 80 0.05 0.10 0.35 20
q q q q
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)
VCC - 1.25 -7 -8 VCC - 2.5 15 20 0.1 0.5
q q
Measured at AVG2 Pin Measured at PROG2 Pin IMODE = 0.5mA IMODE = 10mA
q q
0.5 1.2
The q denotes specifications which apply over the full operating temperature range.
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-.
PI FU CTIO S
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 2.5k 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
PI FU CTIO S
input (across external sense resistor) equal to (VCC - VPROG)/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 5k typical output impedance. 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 equals (VCC - VPROG2)/20. Input voltage range is (VCC - 0.15V) to (VCC - 2.5V). GND: Ground Reference. MODE: Comparator Open Collector Output. Output is logic low when magnitude of current sense amplifier differential input voltage is less than (VCC - VPROG2)/20. IOUT: Transconductance Amplifier Output. In typical application, IOUT sinks current from current-setting node on companion PWM controller IC, facilitating current mode loop control.
FUNCTIONAL BLOCK DIAGRA
VCC
500
+ -
+ -
IN+
CURRENT SENSE RESISTOR
+
SENSE AMPLIFIER
VID
IN-
-
PROG
PROG2* *AVAILABLE IN THE LT1620GN ONLY
OPERATION
(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.
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5V
(x1 GAIN) SENSE 2.5k (x10 GAIN) 5k AVG
INTVCC SENSE + SENSE -
(x20 GAIN) AVG2*
PWM CONTROLLER
+
gm IOUT ITH
- + -
GND
LT1620/21 * FBD
MODE*
END-OF-CYCLE (ACTIVE LOW)
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
OPERATION
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 130A
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 0.025 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.
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(Refer to the Functional Block Diagram)
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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LT1620/LT1621
APPLICATIONS INFORMATION
R2 1.5M RUN C11, 56pF C13 0.033F X7R C12, 0.1F COSC RUN/SS ITH C14 1nF R1 1k SFB SGND C9, 100pF C17, 0.01F VOSENSE SENSE - SENSE + 5 6 C18 0.1F 7 8 RP1 3k 1% C16 0.1F C15 0.1F C8, 100pF RP2 15.75k 1% RF2 110k 0.1% IN+ VCC IN- GND LT1620MS8 IOUT SENSE 4 3 C10 100pF LTC1435 TG BOOST D1* SW VIN
* D1, D2: CENTRAL SEMICONDUCTOR CMDSH-3
PROG AVG
2 1
RF1 1.44M 0.1%
Figure 2. LT1620/LTC1435 Battery Charger
Charge Current Programming 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 2.5k 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. 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.
Output Float Voltage 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. 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
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+
C4 0.1F C5, 0.1F Si4412DY L1 27H
C1 22F 35V
+
C2 22F 35V
VIN 17.3V TO 28V
RSENSE 0.025
VBATT 16.8V
+
D2* C6 0.1F Si4412DY
INTVCC BG PGND EXTVCC C7 4.7F
C3 22F 35V
Li-ION
LT1620/21 * F02
LT1620/LT1621
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)] 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. 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. 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 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 22F 1 2 SENSE IOUT
CONNECTED AS IN FIGURE 2 LT1620GN SENSE IOUT VEE PROG PROG2 MODE IN- AVG2 VCC IN+ R3 10k C1, 3.3F AVG
+
C2 3.3F
R1 5.5k R2 50k
END-OF-CYCLE (ACTIVE LOW)
Figure 3. End-of-Cycle Flag Implementation with LT1620GN
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C1 1F AVG 8
RP1 3k 1% RP2 12k 1%
C2 1F
7 PROG LT1620MS8 6 3 VCC GND 4 IN- IN+ 5
R1 0.033
+
22F L1B 10H
TO SYSTEM LOAD
MBRS340 7 VIN LT1513 RUN 6 4 S/S GND GND TAB 8 VFB IFB VC 1 0.1F X7R 0.22F RSENSE 0.1 2 3 24 6.4k VSW 5 4.7F L1A 10H 57k
VBATT = 12.3V
+
22F x2
Li-ION
+
LT1620/21 * F03
1620/21 * F04
Figure 4. Input Current Sensing Application
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LT1620/LT1621
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 130A 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 75A. 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 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.
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LT1620/LT1621
APPLICATIONS INFORMATION
40 30 VCC = 5V VID = 80mV VCM = 16.8V
VPROG OFFSET (mV)
VPROG OFFSET (mV)
20 10 0 -10 -20 -30 -40 0
50
200 150 IOUT SINK CURRENT (A)
100
250
LT1620/21 * F05a
Figure 5a. Typical Setpoint Voltage (VPROG) Changes Slightly Depending Upon the Amount of Current Sinked by the IOUT Pin
40 20
VPROG2 OFFSET (mV)
ADDITIONAL INPUT REFERRED OFFSET (mV)
VCC = 5V VCM = 16.8V IOUT = 130A
0 -20 -40 -60 -80
0
20
80 100 120 60 40 IN+ - IN- (VID) INPUT (mV)
140
LT1620/21 * F05c
Figure 5c. Typical Comparator Threshold Voltage (VPROG2) Changes Slightly Depending Upon the Programmed Differential Input Voltage (VID)
10
PROGRAMMING OFFSET (mV)
5 VPROG2 0 VPROG
-5
-10 4.50
Figure 5e. Typical Setpoint Voltages for VPROG and VPROG2 Change Slightly Depending Upon the Supply Voltage (VCC)
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20 10 0 -10 -20 -30 -40 VCC = 5V VCM = 16.8V IOUT = 130A
0
20
80 100 120 60 40 IN+ - IN- (VID) INPUT (mV)
140
LT1620/21 * F05b
Figure 5b. Typical Setpoint Voltage (VPROG) Changes Slightly Depending Upon the Programmed Differential Input Voltage (VID)
14 12 10 8 6 4 2 0 0 4 36 3 5 1 2 IN+, IN- COMMON MODE VOLTAGE (VCM) (V)
LT1620/21 * F05d
VCC = 5V VID = 80mV IOUT = 130A
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
VID = 80mV VCM = 16.8mV IOUT = 130A
4.75
5.00 VCC (V)
5.25
5.50
LT1620/21 * F05e
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LT1620/LT1621
TYPICAL APPLICATIONS
Programmable Constant Current Source
6V TO 28V LT1121CS8-5 8 IN SHDN 5 OUT GND 3 1 D45VH10 0.1 0.1F 470 IOUT 0A TO 1A
0.1F
SHUTDOWN
6V TO 15V
+
22F 25V TPS
4.7k 2N4401 10k 2N4403
5V 0.1F 2N7002 1F 5 6 8 GND AVG2 MODE -IN VCC +IN 820 10k 0.047 F 1 3 4.7k SENSE IOUT AVG 16 14 PROG LT1620GN 13 PROG2 12 11 9 47k IPROG RPROG 20k 0.1F 10k 1%
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1F 18k VN2222LM 2N3904 22 1 2 SENSE IOUT
0.1F AVG 7 PROG LT1620MS8 3 6 VCC GND 4 -IN +IN 5 8 0.1F 10k 1%
IPROG
RPROG
IOUT = (IPROG)(10,000) RPROG = 40k FOR 1A OUTPUT
LT1620/21 * TA01
High Efficiency Buck Constant Current Source
Si9405 50H CTX50-4 0.05 IOUT 0A TO 1A 22F 25V TPS
+
MBRS130T3
2N7002 IOUT = (IPROG)(20,000) RPROG = 90k FOR 1A OUTPUT
LT1620/21 * TA04
33k
LT1620/LT1621
PACKAGE DESCRIPTIO
0.015 0.004 x 45 (0.38 0.10) 0.0075 - 0.0098 (0.191 - 0.249) 0.016 - 0.050 (0.406 - 1.270) 0 - 8 TYP
* 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
0.007 (0.18) 0.021 0.004 (0.53 0.01)
0 - 6 TYP SEATING PLANE
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
0.010 - 0.020 x 45 (0.254 - 0.508) 0.008 - 0.010 (0.203 - 0.254)
0.053 - 0.069 (1.346 - 1.752) 0- 8 TYP
0.014 - 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
0.016 - 0.050 0.406 - 1.270
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.
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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
0.229 - 0.244 (5.817 - 6.198) 0.053 - 0.069 (1.351 - 1.748) 0.004 - 0.009 (0.102 - 0.249) 0.150 - 0.157** (3.810 - 3.988)
0.008 - 0.012 (0.203 - 0.305)
0.025 (0.635) BSC
1
23
4
56
7
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) 0.006 0.004 (0.15 0.10) 0.192 0.004 (4.88 0.10) 0.012 (0.30) 0.118 0.004** (3.00 0.10) 76 5
1
23
4
MSOP08 0596
S8 Package 8-Lead Plastic Small Outline (Narrow 0.150)
(LTC DWG # 05-08-1610)
8 0.189 - 0.197* (4.801 - 5.004) 7 6 5
0.228 - 0.244 (5.791 - 6.197) 0.004 - 0.010 (0.101 - 0.254) 0.150 - 0.157** (3.810 - 3.988)
0.050 (1.270) TYP
1
2
3
4
SO8 0996
11
LT1620/LT1621
TYPICAL APPLICATION
Electronic Circuit Breaker
0.033 5V 0.1F 1k FAULT CDELAY 100 33k 2N3904 1 2 SENSE IOUT AVG 8 1N4148 100k 4.7k 33k 7 PROG LT1620MS8 6 3 VCC GND 4 -IN +IN 5 Si9434DY 5V AT 1A PROTECTED
TYPICAL DC TRIP AT 1.6A 3A FAULT TRIPS IN 2ms WITH CDELAY = 1.0F
RELATED PARTS
PART NUMBER LTC(R)1435 DESCRIPTION High Efficiency Low Noise Synchronous Step-Down Switching Regulator COMMENTS 16-Pin Narrow SO and SSOP, VIN 36V, Programmable Constant Frequency Full-Featured Single Controller, VIN 36V, Programmable Constant Frequency Full-Featured Dual Controllers, VIN 36V, Programmable Constant Frequency Step-Down Charger for Li-Ion, NiCd and NiMH Step-Down Charger that Allows Charging During Computer Operation and Prevents Wall-Adapter Overload
LTC1436/LTC1436-PPL/ High Efficiency Low Noise Synchronous Step-Down LTC1437 Switching Regulator Controllers LTC1438/LTC1439 LT1510 LT1511 LT1512 LT1513 LTC1538-AUX LTC1539 Dual High Efficiency Low Noise Synchronous Step-Down Switching Regulators 1.5A Constant-Current/Constant-Voltage Battery Charger 3.0A Constant-Current/Constant-Voltage Battery Charger with Input Current Limiting
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 Dual High Efficiency Low Noise Synchronous Step-Down Switching Regulator Dual High Efficiency Low Noise Synchronous Step-Down Switching Regulator 5V Standby in Shutdown, VIN 36V, Programmable Constant Frequency 5V Standby in Shutdown, VIN 36V, Programmable Constant Frequency
12
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417 q (408) 432-1900 FAX: (408) 434-0507q TELEX: 499-3977 q www.linear-tech.com
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2N3904
LT1620/21 * TA03
16201f LT/GP 0197 7K * PRINTED IN USA
(c) LINEAR TECHNOLOGY CORPORATION 1996

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