Datasheet

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MAX14920/MAX14921

High-Accuracy 12-/16-Cell Measurement AFEs

19-6496; Rev 0; 10/12

Ordering Information appears at end of data sheet.

For related parts and recommended products to use with this part,

refer to www.maximintegrated.com/MAX14920.related.

Functional Diagram appears at end of data sheet.

EVALUATION KIT AVAILABLE

General Description

The MAX14920/MAX14921 battery measurement analog

front-end devices accurately sample cell voltages and

provide level shifting for primary/secondary battery packs

up to 16 cells/+65V (max). The MAX14920 monitors up

to 12 cells, while the MAX14921 monitors up to 16 cells.

Both devices simultaneously sample all cell voltages,

allowing accurate state-of-charge and source-resistance

determination. All cell voltages are level shifted to ground

reference with unity gain, simplifying external ADC data

conversion.

The devices have a low-noise, low-offset amplifier that

buffers differential voltages of up to +5V, allowing moni-

toring of all common lithium-ion (Li+) cell technologies.

The resulting cell voltage error is Q0.5mV.

The devices’ high accuracy make them ideal for monitoring

cell chemistries with very flat discharge curves, such as

lithium-metal phosphate.

Passive-cell balancing is supported by external FET

drivers. Integrated diagnostics in the devices allow

open-wire detection and undervoltage/overvoltage

alarms. The devices are controlled by a daisy-chainable

SPI interface.

The MAX14920 is available in a 64-pin (10mm x 10mm)

TQFP package with an exposed pad. The MAX14921 is

available in an 80-pin (12mm x 12mm) TQFP package.

Both devices are specified over the -40°C to +85°C

extended temperature range.

Applications

Industrial Battery Backup Systems

Telecom Battery Backup Systems

Energy Storage Packs

e-Transportation Energy Packs

Benefits and Features

S High Accuracy

 ±0.5mV (max) Cell Voltage

Simultaneous Cell Voltage Sampling

Self-Calibration

S Integrated Diagnostics

 Open-Wire and Short Fault Detection

 Undervoltage/Overvoltage Warning

 Thermal Shutdown

S High Flexibility

 SPI Interface

 12-Cell and 16-Cell Versions

 +6V Minimum (3 Cells) Operation

 +0.5V to +4.5V Cell Voltage Range

 Integrated Cell-Balancing FET Drivers

 Integrated 5V LDO

S Low Power

 1µA

Shutdown Mode

 1µA/10µA Cell Current Draw

For pricing, delivery, and ordering information, please contact Maxim Direct

at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com.

Summary of content (29 pages)

PAGE 1
EVALUATION KIT AVAILABLE MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs General Description The MAX14920/MAX14921 battery measurement analog front-end devices accurately sample cell voltages and provide level shifting for primary/secondary battery packs up to 16 cells/+65V (max). The MAX14920 monitors up to 12 cells, while the MAX14921 monitors up to 16 cells. Both devices simultaneously sample all cell voltages, allowing accurate state-of-charge and source-resistance determination.
PAGE 2
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs ABSOLUTE MAXIMUM RATINGS (All voltages referenced to AGND.) VP to AGND ...........................................................-0.3V to +70V LDOIN to AGND ................................ (VA - 0.3V) to (VP + 0.3V) VA to AGND ............................................................-0.3V to +6V CV0, DGND to AGND...........................................-0.3V to +0.3V SCLK, SDI, CS, EN...................................................-0.
PAGE 3
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs DC ELECTRICAL CHARACTERISTICS (continued) (VP = +65V, DGND = AGND, VL = VEN = +3.3V, VA = +5V, CSAMPLE = 1FF, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2) PARAMETER VP UVLO UVLO Hysteresis LDOIN UVLO SYMBOL UV_VPVTH CONDITIONS MIN VP rising UV_VPHYST UV_LDOINVT TYP MAX UNITS +6 V 200 VLDOIN rising +5.25 mV +6 V VA UVLO UV_VAVTH VA rising +4.7 V VL UVLO UV_VLVTH VL rising +1.
PAGE 4
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs DC ELECTRICAL CHARACTERISTICS (continued) (VP = +65V, DGND = AGND, VL = VEN = +3.3V, VA = +5V, CSAMPLE = 1FF, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS VA - 0.3 V Q100 FV ANALOG OUTPUT (AOUT) Output Signal Range Amplifier Offset Voltage VAOUT VOFFSET Temperature Offset Drift Gain Output Error A_V VO_ERR Reference to AGND +0.3 VAOUT = +3.
PAGE 5
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs DC ELECTRICAL CHARACTERISTICS (continued) (VP = +65V, DGND = AGND, VL = VEN = +3.3V, VA = +5V, CSAMPLE = 1FF, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 6
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Timing Diagrams tSET CS SCLK SDI C1 C2 C3 C4 C16 T1 T2 T3 OT AOUT 0V *n = 1–12 (MAX14920) AND n = 1–16 (MAX14921) Figure 1. AOUT Delay from SPI Select tDROOP tSAMPL SAMPL VCVn* 1mV AOUT *n = 1–12 (MAX14920) and n = 1–16 (MAX14921) Figure 2. AOUT Voltage-Droop Time CS tCH tCSS tCSH tCL SCLK tDS tDH SDI tDV tDO tTR SDO Figure 3.
PAGE 7
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Typical Operating Characteristics (VCVn - VCV(n - 1) = +3.3V (where n = 1–12 (MAX14920) and n = 1–16 (MAX14921)), TA = +25°C, unless otherwise noted.) 40 TA = +25°C 30 IP (µA) TA = +85°C TA = -40°C VP = 65V 30 20 20 10 10 0 0 VP = 24V VP = 6V 0.5 VP = 10V 0.4 CHANGE IN OUTPUT VOLTAGE (%) SAMPLE MODE LDO DISABLED 50 40 IP (µA) MAX14920 toc02 SAMPLE MODE LDO DISABLED 50 60 MAX14920 toc01 60 LDO OUTPUT VOLTAGE CHANGE vs.
PAGE 8
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Pin Configurations CT8 CB8 CV7 CT7 BA7 CB7 CV6 BA6 CT6 CB6 CV5 BA5 CT5 CB5 BA4 CV4 TOP VIEW 48 47 46 45 44 43 42 41 40 39 38 37 36 35 34 33 CT4 49 32 BA8 CB4 50 31 CV8 CV3 51 30 CB9 BA3 52 29 CT9 CT3 53 28 BA9 CB3 54 27 CV9 CV2 55 26 CB10 BA2 56 25 CT10 MAX14920 CT2 57 24 BA10 CB2 58 23 CV10 CV1 59 22 CB11 BA1 60 21 CT11 20 BA11 CT1 61 *EP CV0 62 EN 63 19 CV11 18 CB12 + BA12 VP CV12 LDOIN 10 11 1
PAGE 9
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Pin Configurations (continued) CT10 CB10 CV9 BA9 CT9 CB9 CV8 BA8 CT8 CB8 CV7 BA7 CT7 CB7 CV6 59 58 57 56 55 54 53 52 51 50 49 48 47 46 45 44 43 42 41 BA6 CV5 60 CT6 BA5 CB6 TOP VIEW CT5 61 40 BA10 CB5 62 39 CV10 CV4 63 38 CB11 BA4 64 37 CT11 CT4 65 36 BA11 CB4 66 35 CV11 CV3 67 34 CB12 BA3 68 33 CT12 CT3 69 CB3 70 32 BA12 31 CV12 MAX14921 CV2 71 30 CB13 BA2 72 29 CT13 CT2 73 28 BA13 CB2
PAGE 10
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Pin Description PIN MAX14920 (64 TQFP-EP) MAX14921 (80 TQFP) NAME 1 1 SCLK 2 2 SDI 3 3 SDO FUNCTION SPI Clock Input SPI Data Line Input SPI Data Line Output Sample Control Input. Voltages at CV_ inputs are tracked when SAMPL is logichigh. When SAMPL transitions from high to low, the differential voltages on CV_ are held internally and made ready for readout at the AOUT output.
PAGE 11
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Pin Description (continued) PIN MAX14920 (64 TQFP-EP) MAX14921 (80 TQFP) NAME 21 37 CT11 Sampling Capacitor 11 High Terminal. CT11 internally connects to CV11 when SAMPL is logic-high. Connect a 1FF capacitor between CT11 and CB11. Leave CT11 unconnected if not used. 22 38 CB11 Sampling Capacitor 11 Low Terminal. CB11 internally connects to CV10 when SAMPL is logic-high. Connect a 1FF capacitor between CT11 and CB11.
PAGE 12
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Pin Description (continued) PIN MAX14920 (64 TQFP-EP) MAX14921 (80 TQFP) NAME 36 52 BA7 Cell-Balancing Gate Driver Output 7. Connect BA7 to the gate of the external n-channel FET. Leave BA7 unconnected if not used. 37 53 CT7 Sampling Capacitor 7 High Terminal. CT7 internally connects to CV7 when SAMPL is logic-high. Connect a 1FF capacitor between CT7 and CB7. Leave CT7 unconnected if not used.
PAGE 13
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Pin Description (continued) PIN MAX14920 (64 TQFP-EP) MAX14921 (80 TQFP) NAME 51 67 CV3 Cell Voltage Input 3. Connect CV3 to cell anode/cathode. Connect CV3 to the highest voltage of the battery cell stack if not used. 52 68 BA3 Cell-Balancing Gate Driver Output 3. Connect BA3 to the gate of the external n-channel FET. Leave BA3 unconnected if not used. 53 69 CT3 Sampling Capacitor 3 High Terminal.
PAGE 14
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Pin Description (continued) PIN MAX14920 (64 TQFP-EP) MAX14921 (80 TQFP) NAME FUNCTION — 18 CB16 Sampling Capacitor Connection 16 Low Terminal. CB16 internally connects to CV15 when SAMPL is logic-high. Connect a 1FF capacitor between CT16 and CB16. Leave CB16 unconnected if not used. — 19 CV15 Cell Voltage Input 15. Connect CV15 to cell anode/cathode. Connect CV15 to the highest voltage of the battery cell stack if not used.
PAGE 15
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Detailed Description The MAX14920/MAX14921 analog front-end devices are used in multicell battery measurement systems to monitor primary/secondary battery packs up to 16 cells/+65V (max). The devices perform the signal conditioning required for enabling accurate cell voltage measurement.
PAGE 16
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs SAMPLE PHASE HOLD PHASE tSAMPL HOLD DELAY LEVEL SHIFT tD_H tD_LS SETTLING SELECT CELL a tSET CONVERT SELECT CELL a CELL b tSET CONVERT SELECT CELL b CELL c CONVERT SELECT CELL m CELL n tSET CONVERT CELL n = VOLTAGE READY = SPI ACTIVITY = ADC CONVERSION Figure 5. SPI Control Cells Voltage Readout Measurement Accuracy The accuracy of cell voltage monitoring (i.e.
PAGE 17
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs each of the 12/16 cells at AOUT, multiplied by 128. If VERR__CHARGE_INJECTION is large enough to affect the required 1mV accuracy, this calibration method provides a measurement of the parasitic capacitance on each CT_ pin so the microcontroller can use this to correct VERR_INJECTION in its readings. OUTPUT ERROR vs. SAMPLING TIME OUTPUT ERROR (mV) 100.0 VCn = 65V VC = 4.5V CSAMPL = 1µF CPAR = 1pF 10.
PAGE 18
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs read out the total cell stack voltage, set the [ECS, SC0, SC1, SC2, SC3] bits to [0, 0, 0, 1, 1]. The total cell stack voltage can be read during the sample or hold phase. SPI Serial Interface Control of the devices is done through a 24-bit SPI interface. The controller sends the serial data to the devices through the SDI input. The devices simultaneously send out monitoring data at the SDO output.
PAGE 19
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Table 1.
PAGE 20
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Table 2. Cell Selection CELL SC0 SC1 SC2 SC3 1 0 0 0 0 2 1 0 0 0 3 0 1 0 0 4 1 1 0 0 5 0 0 1 0 6 1 0 1 0 7 0 1 1 0 8 1 1 1 0 9 0 0 0 1 10 1 0 0 1 11 0 1 0 1 12 1 1 0 1 13* 0 0 1 1 14* 1 0 1 1 15* 0 1 1 1 16* 1 1 1 1 *For MAX14921 only. Table 3.
PAGE 21
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs SPI Monitoring Bits The monitoring bits provide feedback of undervoltage conditions and thermal shutdown, as well as indication when the devices are ready for operation after power-up. Table 4 describes the diagnostics/monitoring bits that the devices send back to the host controller through the SDO output. Flexible Logic Interface The serial/parallel logic control interface logic levels can be defined to be in a range between +1.
PAGE 22
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Linear Regulator The internal linear regulator has LDOIN as its input voltage and regulates this down to +5V Q5% at the VA output with a load current of 10mA (max). The LDO is automatically enabled when LDOIN is above +5.5V. The internal LDO is short-circuit protected with a current limit higher than 14mA (22mA, typ). An external +5V regulator can be used instead of the internal one.
PAGE 23
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Shorts between cell connections can be detected during normal operation. The cell readout voltage results in ~0V or ~VA depending on where the short happens. In the case of shorts, the maximum currents flowing in/out of the pins must be limited and overvoltages avoided, including the external components (balancing FETs and sampling capacitors).
PAGE 24
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Applications Information Sampling Speed and CapacitorSelection Considerations Capacitor values of 1FF are recommended for achieving low errors and at high sampling rates, with sample and hold times in the order of 5ms. With 1FF capacitors and good PCB layout, charge injection-error correction is normally not required.
PAGE 25
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs 1µF CT16 1µF CB16 CT15 1µF CB15 CT14 CB14 LDOIN T_ VP CV16 POWERSUPPLY UNIT VA BA16 1µF CV15 VA VL MAX14920 MAX14921 1µF BA15 AOUT CV14 MAX11163 16-BIT ADC MAX6126 EXTERNAL REFERENCE SAMPL CV1 SCLK SDO SDI BA1 CS CV0 DGND µC EN AGND CT1 CB2 1µF CT2 1µF CB3 CT3 1µF Figure 11.
PAGE 26
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs COMn SDO CS CLK SDI VCCn GND MAX17501 VP VA SPI2 MAX14920 MAX14921 ADC SDO SPI1 CONTROLLER GND SDI MAX14850 COMn-1 VCCn-1 VCC1 COM1 GND MAX17501 VP VA SPI2 MAX14920 MAX14921 ADC SDO SPI1 CONTROLLER GND SDI MAX14850 MOSI CS CLK MISO CONTROLLER GND VCC Figure 12.
PAGE 27
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs CB16* CT16* CB15* CT15* CB14* CT14* CB13* CT13* CB12 CT12 CB11 CT11 CB10 CT10 CB9 CT9 VP Functional Diagram CV16* BA16* MAX14920 MAX14921 CV15* BA15* CV14* T1 BA14* CV13* T2 BA13* CV12 T3 BA12 CV11 +5V LDO BA11 LDOIN VA CV10 BA10 AOUT CV9 BA9 CV8 EN SOURCE SELECT/ CALIBRATION BA8 CV7 BA7 VL CV6 BA6 CV5 SAMPL BA5 CV4 CS BA4 CV3 SPI BA3 SCLK SDI CV2 BA2 SDO CV1 BA1 DGND CB8 CT8 CB7 CT7 CB6 CT6
PAGE 28
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Package Information Ordering Information TEMP RANGE PINPACKAGE PART CELLS MAX14920ECB+ 12 -40NC to +85NC 64 TQFP-EP* MAX14921ECS+ 16 -40NC to +85NC 80 TQFP +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. Chip Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only.
PAGE 29
MAX14920/MAX14921 High-Accuracy 12-/16-Cell Measurement AFEs Revision History REVISION NUMBER REVISION DATE 0 10/12 Initial release — 1 2/13 Removed future products asterisks from the MAX14920 28 DESCRIPTION PAGES CHANGED Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied.