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19-1121; Rev 0; 9/96
KIT ATION EVALU ABLE AVAIL
Cost-Saving Multichemistry Battery-Charger System
____________________________Features
o o o o Multichemistry Charger System (Li-Ion, NiMH, NiCd) Independent Voltage and Current Loops 0.5% Internal Reference for Li-Ion Cells Lowers Cost: --Stands Alone or Uses Low-Cost C --Built-In 1% Linear Regulator Powers C --Linear Regulator Provides Reference to C ADCs --Built-In C Reset --Controls Low-Cost External PNP Transistor or P-Channel MOSFET o Space-Saving 16-Pin QSOP o Charging-Current-Monitor Output o <1A Battery Drain when Off
_______________General Description
The MAX846A is a cost-saving multichemistry batterycharger system that comes in a space-saving 16-pin QSOP. This integrated system allows different battery chemistries (Li-Ion, NiMH or NiCd cells) to be charged using one circuit. In its simplest application, the MAX846A is a standalone, current-limited float voltage source that charges Li-Ion cells. It can also be paired up with a low-cost microcontroller (C) to build a universal charger capable of charging Li-Ion, NiMH, and NiCd cells. An internal 0.5%-accurate reference allows safe charging of Li-Ion cells that require tight voltage accuracy. The voltage- and current-regulation loops used to control a low-cost external PNP transistor (or P-channel MOSFET) are independent of each other, allowing more flexibility in the charging algorithms. The MAX846A has a built-in 1%, 3.3V, 20mA linear regulator capable of powering the C and providing a reference for the C's analog-to-digital converters. An on-board reset notifies the controller upon any unexpected loss of power. The C can be inexpensive, since its only functions are to monitor the voltage and current and to change the charging algorithms.
MAX846A
______________Ordering Information
PART MAX846AC/D MAX846AEEE TEMP. RANGE 0C to +70C -40C to +85C PIN-PACKAGE Dice* 16 QSOP
________________________Applications
Li-Ion Battery Packs Desktop Cradle Chargers Li-Ion/NiMH/NiCd Multichemistry Battery Chargers Cellular Phones Notebook Computers Hand-Held Instruments
*Dice are tested at TA = +25C only. Contact factory for details.
__________Typical Operating Circuit
3.5V TO 20V
__________________Pin Configuration
TOP VIEW
DCIN 1 VL 2 CCI 3 GND 4 CCV 5 VSET 6 ISET 7 OFFV 8 16 DRV 15 PGND 14 CSDRV CSCS+ DCIN ISET CELL2 GND PGND BATT Li-ION BATTERY
MAX846A
MAX846A
13 CS+ 12 BATT 11 ON 10 CELL2 9 PWROK
VL CCV CCI PWROK ON
QSOP
________________________________________________________________ Maxim Integrated Products
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Cost-Saving Multichemistry Battery-Charger System MAX846A
ABSOLUTE MAXIMUM RATINGS
DCIN, DRV, CS+, CS-, BATT to GND........................-0.3V, +21V PGND to GND.....................................................................0.3V VL to GND......................................................................-0.3V, 7V IPWROK ................................................................................10mA PWROK, ISET, CCI, CCV, OFFV, VSET, CELL2, ON to GND ............................................-0.3V, VL + 0.3V CS+ to CS-..........................................................................0.3V VL Short to GND.........................................................Continuous IDRV ...................................................................................100mA Continuous Power Dissipation (TA = +70C) QSOP (derate 8.3mW/C above +70C) ........................667mW Operating Temperature Range MAX846AEEE ....................................................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.
ELECTRICAL CHARACTERISTICS
(VDCIN = 10V, ON = VL, IVL = IVSET = 0mA, VCS- = VCS+ = 10V, VBATT = 4.5V, VOFFV = VCELL2 = 0V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER VL REGULATOR DCIN Supply Current Operating Range Output Voltage Short-Circuit Current Limit PWROK Trip Level VL Undervoltage-Lockout Level REFERENCE Output Voltage Output Resistance CURRENT-SENSE AMPLIFIER Transconductance Output Offset Current Input Common-Mode Range Maximum Differential Input Voltage CS- Lockout Voltage CS+, CS- Input Current CS+, CS- Off Input Current VISET = 1.7V, VCS+ - VCS- = 165mV VCS+ = 4V Measured at VCS-, VCS+ - VCS- = 165mV VCS- = VISET = 2.1V, CSA transconductance >0.9mA/V When VCS- is less than this voltage, DRV is disabled. VCS+ = 20V, VCS+ -VCS- = 165mV DCIN = VL = ON = GND 0.01 2.1 225 1.9 2.1 250 10 0.95 1 1.05 3 20.0 mA/V A V mV V A A Measured at VSET, IVSET = 0mA, VON = 0V -0.5% -2% 1.650 20 +0.5% +2% V k 0mA < IVL < 20mA, 3.7V < VDCIN < 20V VL = GND Rising VL edge, 2% hysteresis 2.9 2.5 VDCIN = 20V, IDRV = IVL = 0mA 3.7 3.267 3.305 50 3.0 3.1 2.9 5 20.0 3.333 mA V V mA V V CONDITIONS MIN TYP MAX UNITS
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Cost-Saving Multichemistry Battery-Charger System
ELECTRICAL CHARACTERISTICS (continued)
(VDCIN = 10V, ON = VL, IVL = IVSET = 0mA, VCS- = VCS+ = 10V, VBATT = 4.5V, VOFFV = VCELL2 = 0V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C.) PARAMETER VOLTAGE LOOP VVSET = 1.650V, VCELL2 = 0V, IDRV = 1mA, VDRV = 10V VVSET = 1.650V, VCELL2 = VL, IDRV = 1mA, MAX846A VDRV = 10V VSET Common-Mode Input Range CCV Output Impedance Voltage-Loop Load Regulation BATT Input Current BATT Off Input Current CURRENT LOOP Current-Loop Set Point CA Voltage Gain CCI Output Impedance Overcurrent Trip Level DRIVER DRV Sink Current DRV Off Current LOGIC INPUTS AND OUTPUTS Input High Level Input Low Level Input Current PWROK Output Low Level PWROK Output High Leakage CELL2, ON, OFFV CELL2, ON, OFFV CELL2, ON, OFFV IPWROK = 1mA, VDCIN = VVL = 2.5V VPWROK = 3.3V 0.01 2.4 0 0.01 VL 0.8 1 0.4 1 V V A V A VDRV = 3V VDRV = 20V, VON = 0V 20 0.1 100 mA A When VISET exceeds this voltage, DRV current is disabled. 1.90 IDRV = 5mA, VDRV = 10V 1.634 1.650 5 50 2.1 1.666 V V/V k V 1mA < IDRV < 5mA VBATT = 10V, CELL2 = GND or VL VBATT = 10V, ON = GND, CELL2 = GND or VL 0.01 -0.25% -0.25% 1.25 150 0.05 225 1 4.2 8.4 +0.25% V +0.25% 2.0 V k CONDITIONS MIN TYP MAX UNITS
MAX846A
Voltage-Loop Set Point
%
A A
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Cost-Saving Multichemistry Battery-Charger System MAX846A
ELECTRICAL CHARACTERISTICS (Note 1)
(VDCIN = 10V, ON = VL, IVL = IVSET = 0mA, VCS- = VCS+ = 10V, VBATT = 4.5V, VOFFV = VCELL2 = 0V, TA = -40C to +85C, unless otherwise noted.) PARAMETER VL REGULATOR DCIN Supply Current Output Voltage PWROK Trip Level VL Undervoltage-Lockout Level REFERENCE Output Voltage Output Resistance CURRENT-SENSE AMPLIFIER Transconductance Output Offset Current CS+, CS- Off Input Current VOLTAGE LOOP VVSET = 1.650V, VCELL2 = 0V, IDRV = 1mA, MAX846A VDRV = 10V VVSET = 1.650V, VCELL2 = VL, IDRV = 1mA, VDRV = 10V BATT Off Input Current CURRENT LOOP Current-Loop Set Point Overcurrent Trip Level DRIVER DRV Sink Current DRV Off Current VDRV = 3V VDRV = 20V, ON = GND 20 100 mA A IDRV = 5mA, VDRV = 10V When VISET exceeds this voltage, DRV current is disabled. 1.625 1.86 1.675 2.14 V V VBATT = 10V, ON = GND, CELL2 = GND or VL -0.35% -0.35% 4.2 8.4 +0.35% V +0.35% 1 A VISET = 1.7V, VCS+ - VCS- = 165mV VCS+ = 4V VON = 0V, VCS+ = VCS- = 10V 0.93 1.07 5 10 mA/V A A Measured at VSET, IVSET = 0mA, VON = 0V -0.7% -2% 1.650 20 +0.7% +2% V k VDCIN = 20V, IDRV = IVL = 0mA 0mA < IVL < 20mA, 3.7V < VDCIN < 20V Rising VL edge, 2% hysteresis 3.259 2.9 2.5 5 3.341 3.1 3.0 mA V V V CONDITIONS MIN TYP MAX UNITS
Voltage-Loop Set Point
Note 1: Specifications to -40C are guaranteed by design and not production tested.
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Cost-Saving Multichemistry Battery-Charger System
__________________________________________Typical Operating Characteristics
(TA = +25C, unless otherwise noted.) CURRENT-SENSE AMPLIFIER TRANSCONDUCTANCE vs. ISET VOLTAGE
1.030 1.025 CSA GM (mA/V) 1.020 1.015 1.010 1.005 1.000 0.995 0.990 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 ISET VOLTAGE (V) V = 200mV V = 250mV 0 0 1 2 3 4 5 6 7 8 9 10 BATT VOLTAGE (V) V = 100mV V = 165mV V = VCS+ - VCSMAX846-01
MAX846A
BATTERY INPUT CURRENT vs. BATTERY VOLTAGE
CELL2 = VL 70 BATT INPUT CURRENT (A) CELL2 = GND 60 50 40 30 20 10 OFF ON 128k 82k
MAX846-02
1.035
80
CURRENT-LOOP GAIN
80 70 60 50 GAIN (dB) 40 30 20 10 0 -10 -20 10 100 1k 10k 100k FREQUENCY (Hz) PHASE GAIN CCCI = 10nF
MAX846-03
VOLTAGE-LOOP GAIN
180 150 120 PHASE (DEGREES) 90 60 30 0 -30 -60 -90 -120 1M GAIN (dB) 40 30 20 10 0 -10 -20 -30 -40 -50 -60 10 100 1k 10k 100k FREQUENCY (Hz) = - Charging at 100mA = -Charging at 200mA 2 Li-Ion Cells CCCV = 10nF COUT = 4.7F TIP2955 PNP PASS TRANSISTOR GAIN PHASE
MAX846-04
180 150 120 PHASE (DEGREES) 90 60 30 0 -30 -60 -90
--120 1M
Li-ION CHARGING PROFILE
900 800 CHARGING CURRENT (mA) 700 600 500 400 300 200 100 0 0 60 120 TIME (MINUTES) 180 240 CHARGING CURRENT BATTERY VOLTAGE
MAX846-04
9.0 8.8 8.6 8.4 8.2 8.0 7.8 7.6 7.4 7.2 7.0 BATTERY VOLTAGE (V)
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Cost-Saving Multichemistry Battery-Charger System MAX846A
______________________________________________________________Pin Description
PIN 1 2 3 4 5 6 NAME DCIN VL CCI GND CCV VSET FUNCTION Supply Input from External DC Source. 3.7V VDCIN 20V. 3.3V, 20mA, 1% Linear-Regulator Output. VL powers the system C and other components. Bypass to GND with a 4.7F tantalum or ceramic capacitor. Current-Regulation-Loop Compensation Pin. Connect a compensation capacitor (typically 10nF) from CCI to VL. Ground Voltage-Regulation-Loop Compensation Pin. Connect a compensation capacitor (typically 10nF) from CCV to VL. Float-Voltage Reference-Adjust Input. Leave VSET open for a 4.2V default. See the Applications Information section for adjustment information. Current-Set Input/Current-Monitor Output. ISET sets the current-regulation point. Connect a resistor from ISET to GND to monitor the charging current. ISET voltage is regulated at 1.65V by the currentregulation loop. To adjust the current-regulation point, either modify the resistance from ISET to ground or connect a fixed resistor and adjust the voltage on the other side of the resistor (Figure 5). The transconductance of the current-sense amplifier is 1mA/V. Logic Input that disables the voltage-regulation loop. Set OFFV high for NiCd or NiMH batteries. Open-Drain, Power-Good Output to C. PWROK is low when VL is less than 3V. The reset timeout period can be set externally using an RC circuit (Figure 3). Digital Input. CELL2 programs the number of Li-Ion cells to be charged. A high level equals two cells; a low level equals one cell. Charger ON/OFF Input. When low, the driver section is turned off and IBATT <1A. The VL regulator is always active. Battery Input. Connect BATT to positive battery terminal. Current-Sense Amplifier High-Side Input. Connect CS+ to the sense resistor's power-source side. The sense resistor may be placed on either side of the pass transistor. Current-Sense Amplifier Low-Side Input. Connect CS- to the sense resistor's battery side. Power Ground External Pass Transistor (P-channel MOSFET or PNP) Base/Gate Drive Output. DRV sinks current only.
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ISET
8 9 10 11 12 13 14 15 16
OFFV PWROK CELL2 ON BATT CS+ CSPGND DRV
_______________Detailed Description
The MAX846A battery-charging controller combines three functional blocks: a 3.3V precision, low-dropout linear regulator (LDO), a precision voltage reference, and a voltage/current regulator (Figure 1).
Voltage Reference
The precision internal reference provides a voltage to accurately set the float voltage for lithium-ion (Li-Ion) battery charging. The reference output connects in series with an internal, 2%-accurate, 20k resistor. This allows the float voltage to be adjusted using one external 1% resistor (R VSET ) to form a voltage divider (Figure 4). The float-voltage accuracy is important for battery life and to ensure full capacity in Li-Ion batteries. Table 1 shows the accuracies attainable using the MAX846A.
Linear Regulator
The LDO regulator output voltage (VL) is two times the internal reference voltage; therefore, the reference and LDO track. VL delivers up to 20mA to an external load and is short-circuit protected. The power-good output (PWROK) provides microcontroller (C) reset and charge-current inhibition.
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Cost-Saving Multichemistry Battery-Charger System
Voltage/Current Regulator
The voltage/current regulator consists of a precision attenuator, voltage loop, current-sense amplifier, and current loop. The attenuator can be pin programmed to set the regulation voltage for one or two Li-Ion cells (4.2V and 8.4V, respectively). The current-sense amplifier is configured to sense the battery current on the high side. It is, in essence, a transconductance amplifier converting the voltage across an external sense resistor (RCS) to a current, and applying this current to an external load resistor (RISET). Set the charge current by selecting RCS and RISET. The charge current can also be adjusted by varying the voltage at the low side of RISET or by summing/subtracting current from the ISET node (Figure 5). The voltage and current loops are individually compensated using external capacitors at CCV and CCI, respectively. The outputs of these two loops are OR'ed together and drive an open-drain, internal N-channel MOSFET transistor sinking current to ground. An external P-channel MOSFET or PNP transistor pass element completes the loop. PNP to prevent self-oscillation (due to the high-impedance base drive). Similarly, the CCV output impedance (150k) and the CCV capacitor set the voltage-loop dominant pole. In Figure 2, the compensation capacitance is 10nF, which places a dominant pole at 200Hz. The battery impedance directly affects the voltage-loop DC and high-frequency gain. At DC, the loop gain is proportional to the battery resistance. At higher frequencies, the AC impedance of the battery and its connections introduces an additional high-frequency zero. A 4.7F output capacitor in parallel with the battery, mounted close to BATT, minimizes the impact of this impedance. The effect of the battery impedance on DC gain is noticeable in the Voltage-Loop-Gain graph (see Typical Operating Characteristics). The solid line represents voltage-loop gain versus frequency for a fully charged battery, when the battery energy level is high and the ESR is low. The charging current is 100mA. The dashed line shows the loop gain with a 200mA charging current, a lower amount of stored energy in the battery, and a higher battery ESR.
MAX846A
Stability
The Typical Operating Characteristics show the loop gains for the current loop and voltage loop. The dominant pole for each loop is set by the compensation capacitor connected to each capacitive compensation pin (CCI, CCV). The DC loop gains are about 50dB for the current loop and about 33dB for the voltage loop, for a battery impedance of 250m. The CCI output impedance (50k) and the CCI capacitor determine the current-loop dominant pole. In Figure 2, the recommended CCCV is 10nF, which places a dominant pole at 300Hz. There is a high-frequency pole, due to the external PNP, at approximately fT/. This pole frequency (on the order of a few hundred kilohertz) will vary with the type of PNP used. Connect a 10nF capacitor between the base and emitter of the
__________Applications Information
Stand-Alone Li-Ion Charger
Figure 2 shows the stand-alone configuration of the MAX846A. Select the external components and pin configurations as follows: * Program the number of cells: Connect CELL2 to GND for one-cell operation, or to VL for two-cell operation. * Program the float voltage: Connect a 1% resistor from VSET to GND to adjust the float voltage down, or to VL to adjust it up. If VSET is unconnected, the float voltage will be 4.2V per cell. Let the desired float voltage per cell be VF, and calculate the resistor value as follows:
Table 1. Float-Voltage Accuracy
ERROR SOURCE Internal-reference accuracy VSET error due to external divider. Calculated from a 2% internal 20k resistor tolerance and a 1% external RVSET resistor tolerance. The total error is 3% x (adjustment). Assume max adjustment range of 5%. VSET amplifier and divider accuracy TOTAL ERROR 0.5% 0.15% 0.25% 0.9%
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Cost-Saving Multichemistry Battery-Charger System MAX846A
DC INPUT 3.5V TO 20V 0.01F RDRV 660 (OR P-CHANNEL)
DCIN 3.3V TO C VL 4.7F PGND GND OR DAC TO ADC 3.3V, 1% LDO BST
DRV CS+ 1k N CSA RCS 165m IBATT CS-
ISET 10k VL 2V CL VL 5nF CCI
1.65V VL CA 5nF CCV BATT VA VA 4.7F 2 Li 1 Li OFF ON OPEN OR DAC RVSET VSET 400k, 1% (5% ADJ) 20k, 2% 1.65V, 0.5% REF REFOK CS- > 2V DRV ENABLE PWROK TO C N VL Li OR Ni
CELL2 OFFV
N
GND
MAX846A
VL > 3V
ON ON OFF
Figure 1. Functional Diagram
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Cost-Saving Multichemistry Battery-Charger System MAX846A
(0.165V) I
BATT
EXTERNAL PASS TRANSISTOR CAN BE EITHER PNP OR PMOS FET.
DCIN 3.7V TO 20V
RCS
10nF RDRV 660
4.7F
CS+ DCIN
CS-
DRV
BATT RVSET VSET
VL ADJUST (UP) (DOWN)
VL
MAX846A
100k 10k PWROK ON 0.01F CCI VL CCV 0.01F OFFV 4.7F GND PGND CELL2 (1 CELL) (2 CELLS) ISET RISET
Figure 2. Stand-Alone Li-Ion Charger
4.2 VX - VF 1.65 VF - 4.2
RVSET = 20k
* Calculate RCS and RISET as follows: RCS = VCS / IBATT RISET (in k) = 1.65V / VCS where the recommended value for VCS is 165mV. * Connect ON to PWROK to prevent the charge current from turning on until the voltages have settled. Minimize power dissipation in the external pass transistor. Power dissipation can be controlled by setting the DCIN input supply as low as possible, or by making VDCIN track the battery voltage.
where VX is either GND or VL, and VF is the per-cell float voltage. In the circuit of Figure 1, R VSET is 400k. RVSET and the internal 20k resistor form a divider, resulting in an adjustment range of approximately 5%. The current-regulation loop attempts to maintain the voltage on ISET at 1.65V. Selecting resistor RISET determines the reflected voltage required at the currentsense amplifier input.
Microprocessor-Controlled Multichemistry Operation
The MAX846A is highly adjustable, allowing for simple interfacing with a low-cost C to charge Ni-based and Li-Ion batteries using one application circuit (Figure 3).
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Cost-Saving Multichemistry Battery-Charger System MAX846A
P DCIN 3.7V TO 20V
Li OR Ni
CS+ DCIN
CS-
DRV BATT
ADC (MEASURE V(BATT)) CCI CCV
MAX846A
ON CELL2 OFFV VSET ISET GND PGND PWROK
I/O (LOW = TURN OFF CHARGE) I/O (HIGH = 2 Li CELLS) I/O (HIGH = DISABLE FLOAT V) PWM/DAC (CONTROL FLOAT V) PWM/DAC (CONTROL CHARGE I) ADC (MEASURE IBATT)
VL
VDD MICROCONTROLLER RST
Figure 3. Desktop Multichemistry Charger Concept
Component selection is similar to that of stand-alone operation. By using DACs or C PWM outputs, the float voltage and charging current can be adjusted by the C. When a Ni-based battery is being charged, disable the float-voltage regulation using the OFFV input. The C can also monitor the charge current through the battery by reading the ISET output's voltage using its ADC. Similarly, the battery voltage can be measured using a voltage divider from the battery. Note that the C only needs to configure the system for correct voltage and current levels for the battery being charged, and for Ni-based batteries to detect end-ofcharge and adjust the current level to trickle. The controller is not burdened with the regulation task.
Float-voltage accuracy is important for battery life and for reaching full capacity for Li-Ion batteries. Table 1 shows the accuracy attainable using the MAX846A. For best float-voltage accuracy, set the DRV current to 1mA (RDRV = 660 for a PNP pass transistor).
High-Power Multichemistry Offline Charger
The circuit in Figure 6 minimizes power dissipation in the pass transistor by providing optical feedback to the input power source. The offline AC/DC converter maintains 1.2V across the PNP. This allows much higher charging currents than can be used with conventional power sources.
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Cost-Saving Multichemistry Battery-Charger System MAX846A
MAX846A
20k 1.65V 2% VSET 400k 1% n 0 TO VL DAC 1.65V 2%
MAX846A
20k VSET 400k 1%
0
100% C PWM OUTPUT
WITH VOLTAGE OUTPUT DAC
WITH PWM FROM MICROCONTROLLER
Figure 4. VSET Adjustment Methods
MAX846A
ISET 20k DAC 20k n
MAX846A
ISET 10k 10k
0
100% C PWM OUTPUT
20k
WITH VOLTAGE OUTPUT DAC
WITH PWM FROM MICROCONTROLLER
Figure 5. ISET Adjustment Methods
OPTO-COUPLER
FEEDBACK
AC/DC CONVERTER
MAX846
MICRO CONTROLLER
Figure 6. Low-Cost Desktop Multichemistry Charger Concept
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Cost-Saving Multichemistry Battery-Charger System MAX846A
___________________Chip Topography
VL DCIN DRV PGND
CCI
CS-
CS+ GND BATT CCV 0.105" (2.67mm)
VSET
ON
ISET OFFV
PWROK CELL2
0.085" (2.165mm)
SUBSTRATE CONNECTED TO GND TRANSISTOR COUNT: 349
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
12 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 (c) 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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