UNITRODE bq2010 Technical data

BQ2010SN-D107

Features

Conservative and repeatable measurement of available charge in rechargeable batteries

Designed for battery pack integration

-120 A typical standby current

-Small size enables imple-

mentations in as little as 12 square inch of PCB

Integrate within a system or as a stand-alone device

-Display capacity via singlewire serial communication port or direct drive of LEDs

Measurements compensated for current and temperature

Self-discharge compensation using internal temperature sensor

Accurate measurements across a wide range of current (> 500:1)

16-pin narrow SOIC

bq2010

General Description

The bq2010 Gas Gauge IC is intended for battery-pack or in-system installation to maintain an accurate record of a battery's available charge. The IC monitors a voltage drop across a sense resistor connected in series between the negative battery terminal and ground to determine charge and discharge activity of the battery.

NiMH and NiCd battery self-dis- charge is estimated based on an internal timer and temperature sensor. Compensations for battery temperature and rate of charge or discharge are applied to the charge, discharge, and self-discharge calculations to provide available charge information across a wide range of operating conditions. Battery capacity is automatically recalibrated, or “learned,” in the course of a discharge cycle from full to empty.

Nominal available charge may be directly indicated using a fiveor six-segment LED display. These segments are used to indicate graphically the nominal available charge.

Gas Gauge IC

The bq2010 supports a simple single-line bidirectional serial link to an external processor (common ground). The bq2010 outputs battery information in response to external commands over the serial link.

The bq2010 may operate directly from 3 or 4 cells. With the REF output and an external transistor, a simple, inexpensive regulator can be built to provide VCC across a greater number of cells.

Internal registers include available charge, temperature, capacity, battery ID, battery status, and programming pin settings. To support subassembly testing, the outputs may also be controlled. The external processor may also overwrite some of the bq2010 gas gauge data registers.

Pin Connections							Pin Names
							LCOM	LED common output	REF		Voltage reference output
							SEG1/PROG1	LED segment 1/	NC		No connect
LCOM		1	16		VCC			program 1 input	DQ		Serial communications
SEG1/PROG1		2	15		REF		SEG2/PROG2	LED segment 2/			input/output
SEG2/PROG2		3	14		NC			program 2 input	EMPTY		Empty battery indicator
SEG3/PROG3		4	13		DQ		SEG3/PROG3	LED segment 3/			output
								program 3 input	SB		Battery sense input
SEG4/PROG4		5	12		EMPTY		SEG4/PROG4	LED segment 4/
									DISP		Display control input
SEG5/PROG5		6	11		SB			program 4 input
									SR		Sense resistor input
							SEG5/PROG5	LED segment 5/
SEG6/PROG6		7	10		DISP
V		8	9		SR			program 5 input	VCC		3.0–6.5V
SS							SEG6/PROG6	LED segment 6/
									VSS		System ground
	16-Pin Narrow SOIC							program 6 input
			PN201001.eps
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bq2010

Pin Descriptions

LCOM	LED common output
	Open-drain output switches VCC to source
	current for the LEDs. The switch is off dur-
	ing initialization to allow reading of the soft
	pull-up or pull-down program resistors.
	LCOM is also high impedance when the dis-
	play is off.
SEG1–	LED display segment outputs (dual func-
SEG6	tion with PROG1–PROG6)
	Each output may activate an LED to sink
	the current sourced from LCOM.

PROG1– Programmed full count selection inputs

PROG2	(dual function with SEG1–SEG2)
	These three-level input pins define the pro-
	grammed full count (PFC) thresholds de-
	scribed in Table 2.
PROG3–	Gas gauge rate selection inputs (dual
PROG4	function with SEG3–SEG4)
	These three-level input pins define the scale
	factor described in Table 2.
PROG5	Self-discharge rate selection (dual func-
	tion with SEG5)
	This three-level input pin defines the
	selfdischarge compensation rate shown in Ta-
	ble 1.
PROG6	Display mode selection (dual function
	with SEG6)
	This three-level pin defines the display op-
	eration shown in Table 1.
NC	No connect

SR		Sense resistor input
		The voltage drop (VSR) across the sense re-
		sistor RS is monitored and integrated over
		time to interpret charge and discharge activ-
		ity. The SR input is tied to the high side of
		the sense resistor. VSR < VSS indicates dis-
		charge, and VSR > VSS indicates charge. The
		effective voltage drop, VSRO, as seen by the
		bq2010 is VSR + VOS (see Table 5).
		Display control input
DISP
			high disables the LED display.
		DISP		DISP
		tied to VCC allows PROGX to connect directly
		to VCC or VSS instead of through a pull-up or
		pull-down resistor. DISP floating allows the
		LED display to be active during discharge or
		charge if the NAC registers update at a rate
		equivalent to |VSRO| ≥ 4mV. DISP low acti-
		vates the display. See Table 1.
SB		Secondary battery input
		This input monitors the single-cell voltage
		potential through a high-impedance resis-
		tive divider network for end-of-discharge
		voltage (EDV) thresholds, maximum charge
		voltage (MCV), and battery removed.
EMPTY		Battery empty output
		This open-drain output becomes high-impedance
		on detection of a valid end-of-discharge voltage
		(VEDVF) and is low following the next application
		of a valid charge.
DQ		Serial I/O pin
		This is an open-drain bidirectional pin.
REF		Voltage reference output for regulator
		REF provides a voltage reference output for
		an optional micro-regulator.
VCC		Supply voltage input
VSS		Ground

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bq2010

Functional Description

General Operation

The bq2010 determines battery capacity by monitoring the amount of charge input to or removed from a rechargeable battery. The bq2010 measures discharge and charge currents, estimates self-discharge, monitors the battery for low-battery voltage thresholds, and compensates for temperature and charge/discharge rates. The charge measurement derives from monitoring the voltage across a small-value series sense resistor between the negative battery terminal and ground. The available battery charge is determined by monitoring this voltage over time and correcting the measurement for the environmental and operating conditions.

Figure 1 shows a typical battery pack application of the bq2010 using the LED display capability as a chargestate indicator. The bq2010 can be configured to display capacity in either a relative or an absolute display mode. The relative display mode uses the last measured discharge capacity of the battery as the battery “full” reference. The absolute display mode uses the programmed full count (PFC) as the full reference, forcing each segment of the display to represent a fixed amount of charge. A push-button display feature is available for momentarily enabling the LED display.

The bq2010 monitors the charge and discharge currents as a voltage across a sense resistor (see RS in Figure 1). A filter between the negative battery terminal and the SR pin may be required if the rate of change of the battery current is too great.

		R1
bq2010		Q1
Gas Gauge IC
		ZVNL110A
	REF	C1
		0.1 F	RB1
LCOM	VCC	V
		CC
SEG1/PROG1	SB	VCC
SEG2/PROG2			RB
			2
SEG3/PROG3	DISP
SEG4/PROG4	SR
SEG5/PROG5			R
			S
SEG6/PROG6	VSS
	EMPTY
	DQ
Indicates optional.			Charger

Directly connect to VCC across 3 or 4 cells (3 to 5.6V nominal) with a resistor and a Zener diode to limit voltage during charge. Otherwise, R1, C1, and Q1 are needed for regulation of >4 cells. The value of R1 depends on the number of cells.

Load

Programming resistors (6 max.) and ESD-protection diodes are not shown.

R-C on SR may be required, application-specific.

FG201001.eps

Figure 1. Battery Pack Application Diagram—LED Display

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bq2010

Voltage Thresholds

In conjunction with monitoring VSR for charge/discharge currents, the bq2010 monitors the single-cell battery potential through the SB pin. The single-cell voltage potential is determined through a resistor/divider network according to the following equation:

RB1 = N − 1

RB2

where N is the number of cells, RB1 is connected to the positive battery terminal, and RB2 is connected to the negative battery terminal. The single-cell battery voltage is monitored for the end-of-discharge voltage (EDV) and for maximum cell voltage (MCV). EDV threshold levels are used to determine when the battery has reached an “empty” state, and the MCV threshold is used for fault detection during charging.

Two EDV thresholds for the bq2010 are fixed at:

VEDV1 (early warning) = 1.05V

VEDVF (empty) = 0.95V

If VSB is below either of the two EDV thresholds, the associated flag is latched and remains latched, independent of VSB, until the next valid charge. EDV monitoring may be disabled under certain conditions as described in the next paragraph.

During discharge and charge, the bq2010 monitors VSR for various thresholds. These thresholds are used to compensate the charge and discharge rates. Refer to the count compensation section for details. EDV monitoring is disabled if VSR ≤ -250mV typical and resumes 12 second after VSR > -250mV.

charge display translation. The temperature range is available over the serial port in 10°C increments as shown below:

TMPGG (hex)	Temperature Range
0x	< -30°C
1x	-30°C to -20°C
2x	-20°C to -10°C
3x	-10°C to 0°C
4x	0°C to 10°C
5x	10°C to 20°C
6x	20°C to 30°C
7x	30°C to 40°C
8x	40°C to 50°C
9x	50°C to 60°C
Ax	60°C to 70°C
Bx	70°C to 80°C
Cx	> 80°C

EMPTY Output

The EMPTY output switches to high impedance when VSB < VEDVF and remains latched until a valid charge occurs. The bq2010 also monitors VSB relative to VMCV, 2.25V. VSB falling from above VMCV resets the device.

Reset

The bq2010 recognizes a valid battery whenever VSB is greater than 0.1V typical. VSB rising from below 0.25V or falling from above 2.25V resets the device. Reset can also be accomplished with a command over the serial port as described in the Reset Register section.

Temperature

The bq2010 internally determines the temperature in 10°C steps centered from -35°C to +85°C. The temperature steps are used to adapt charge and discharge rate compensations, self-discharge counting, and available

Layout Considerations

The bq2010 measures the voltage differential between the SR and VSS pins. VOS (the offset voltage at the SR pin) is greatly affected by PC board layout. For optimal results, the PC board layout should follow the strict rule of a single-point ground return. Sharing high-current ground with small signal ground causes undesirable noise on the small signal nodes. Additionally:

The capacitors (SB and VCC) should be placed as close as possible to the SB and VCC pins, respectively,

and their paths to VSS should be as short as possible. A high-quality ceramic capacitor of 0.1µf is recommended for VCC.

The sense resistor capacitor should be placed as close as possible to the SR pin.

The sense resistor (RSNS) should be as close as possible to the bq2010.

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bq2010

Gas Gauge Operation

The operational overview diagram in Figure 2 illustrates the operation of the bq2010. The bq2010 accumulates a measure of charge and discharge currents, as well as an estimation of self-discharge. Charge and discharge currents are temperature and rate compensated, whereas self-discharge is only temperature compensated.

The main counter, Nominal Available Charge (NAC), represents the available battery capacity at any given time. Battery charging increments the NAC register, while battery discharging and self-discharge decrement the NAC register and increment the DCR (Discharge

Count Register).

The Discharge Count Register (DCR) is used to update the Last Measured Discharge (LMD) register only if a complete battery discharge from full to empty occurs without any partial battery charges. Therefore, the bq2010 adapts its capacity determination based on the actual conditions of discharge.

The battery's initial capacity is equal to the Programmed Full Count (PFC) shown in Table 2. Until LMD is updated, NAC counts up to but not beyond this threshold during subsequent charges. This approach allows the gas gauge to be charger-independent and compatible with any type of charge regime.

1.Last Measured Discharge (LMD) or learned battery capacity:

LMD is the last measured discharge capacity of the

battery. On initialization (application of VCC or battery replacement), LMD = PFC. During subsequent discharges, the LMD is updated with the latest measured capacity in the Discharge Count Register (DCR) representing a discharge from full to below EDV1. A qualified discharge is necessary for a capacity transfer from the DCR to the LMD register. The LMD also serves as the 100% reference threshold used by the relative display mode.

2.Programmed Full Count (PFC) or initial battery capacity:

The initial LMD and gas gauge rate values are pro-

grammed by using PROG1–PROG4. The PFC also provides the 100% reference for the absolute display mode. The bq2010 is configured for a given application by selecting a PFC value from Table 2. The correct PFC may be determined by multiplying the rated battery capacity in mAh by the sense resistor value:

Battery capacity (mAh) * sense resistor (Ω) = PFC (mVh)

Selecting a PFC slightly less than the rated capacity for absolute mode provides capacity above the full reference for much of the battery's life.

Inputs

Charge

Discharge

Self-Discharge

Current

Current

Timer

Rate and

Rate and

Temperature

Temperature

Temperature

Compensation

Compensation

Compensation

- -

+

+

+

Nominal

Last

Discharge

Main Counters

Available

< Measured

Count

Qualified

and Capacity

Charge

Discharged

Register

(NAC)

(LMD)

Transfer

(DCR)

Reference (LMD)

Temperature Step,

Temperature

Translation

Other Data

Outputs

Chip-Controlled

Serial

Available Charge

Port

LED Display

FG201002.eps

Figure 2. Operational Overview

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bq2010

Example: Selecting a PFC Value

Given:

Sense resistor = 0.1Ω

Number of cells = 6

Capacity = 2200mAh, NiCd battery Current range = 50mA to 2A

Absolute display mode

Serial port only Self-discharge = C 64

Voltage drop over sense resistor = 5mV to 200mV

Therefore:

2200mAh * 0.1Ω = 220mVh

Select:

PFC = 33792 counts or 211mVh

PROG1 = float

PROG2 = float

PROG3 = float

PROG4 = low

PROG5 = float

PROG6 = float

The initial full battery capacity is 211mVh

(2110mAh) until the bq2010 “learns” a new capacity with a qualified discharge from full to EDV1.

Table 1. bq2010 Programming

	Pin	PROG5
			PROG6		DISP
Connection		Self-Discharge Rate	Display Mode	Display State
	H	Disabled	Absolute	LED disabled
			NAC = PFC on reset
	Z	NAC	Absolute	LED-enabled on discharge or charge
		64	NAC = 0 on reset	when equivalent |VSRO| ≥ 4mV
	L	NAC	Relative	LED on
		47	NAC = 0 on reset
Note:	PROG5 and PROG6 states are independent.

Table 2. bq2010 Programmed Full Count mVh Selections

			Pro-
			grammed		PROG4 = L
	PROGx		Full					PROG4 = Z
			Count
	1	2	(PFC)	PROG3 = H	PROG3 = Z	PROG3 = L	PROG3 = H	PROG3 = Z	PROG3 = L	Units
	-	-	-	Scale =	Scale =	Scale =	Scale =	Scale =	Scale =	mVh/
				1/80	1/160	1/320	1/640	1/1280	1/2560	count
	H	H	49152	614	307	154	76.8	38.4	19.2	mVh
	H	Z	45056	563	282	141	70.4	35.2	17.6	mVh
	H	L	40960	512	256	128	64.0	32.0	16.0	mVh
	Z	H	36864	461	230	115	57.6	28.8	14.4	mVh
	Z	Z	33792	422	211	106	53.0	26.4	13.2	mVh
	Z	L	30720	384	192	96.0	48.0	24.0	12.0	mVh
	L	H	27648	346	173	86.4	43.2	21.6	10.8	mVh
	L	Z	25600	320	160	80.0	40.0	20.0	10.0	mVh
	L	L	22528	282	141	70.4	35.2	17.6	8.8	mVh
	VSR equivalent to 2			90	45	22.5	11.25	5.6	2.8	mV
	counts/sec. (nom.)

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