UNITRODE bq2007 Technical data

BQ2007

Features

Fast charging and conditioning of NiCd and NiMH batteries

-Precise charging independent of battery pack number of cells

-Discharge-before-charge on demand

-Pulse trickle charge conditioning

-Battery undervoltage and overvoltage protection

Built-in 10-step voltage-based charge status monitoring

-Charge status display options include seven-segment monotonic bargraph and fully decoded BCD digit

-Display interface options for direct drive of LCD or LED segments

-Charger state status indicators for pending, discharge, charge, completion, and fault

bq2007

-Audible alarm for charge completion and fault conditions

Charge control flexibility

-Fast or Standard speed charging

-Top-off mode for NiMH

-Charge rates from C8 to 2C

(30 minutes to 8 hours)

Charge termination by:

-Negative delta voltage (-∆V)

-Peak voltage detect (PVD)

-Maximum voltage

-Maximum time

-Maximum temperature

High-efficiency switch-mode design

-Ideal for small heat-sensitive enclosures

24-pin, 300-mil SOIC or DIP

Fast-Charge IC

General Description

The bq2007 is a highly integrated monolithic CMOS IC designed to provide intelligent battery charging and charge status monitoring for standalone charge systems.

The bq2007 provides a wide variety of charge status display formats. The bq2007 internal charge status monitor supports up to a seven-segment bargraph or a single BCD digit display. The bargraph display indicates up to seven monotonic steps, whereas the BCD digit counts in ten steps of 10% increments. The bq2007 output drivers can direct-drive either an LCD or LED display.

Charge action begins either by application of the charging supply or by replacement of the battery pack. For safety, charging is inhibited until battery temperature and voltage are within configured limits.

Pin Connections

Pin Names

SEGC/

Display output segment C/

SNS

Sense resistor input

MSEL

driver mode select

BAT

Battery voltage

SEGB

Display output segment B

TS

Temperature sense

SEGA

Display output segment A

SEGC/MSEL

1

24

SEGD/DSEL1

DIS

Discharge control

LED1

Charge status output 1

SEGB

2

23

SEGE/DSEL2

SEGA

3

22

SEGF/MULT

VSS

System ground

LED1

4

21

SEGG/QDSEL

LED2

Charge status output 2

LED2

5

20

MOD

VCC

5.0V ±10% power

INH

6

19

VCC

INH

Charge inhibit input

COM

7

18

VSS

MOD

Modulation control

ALARM

8

17

DIS

COM

Common LED/LCD output

TM

9

16

TS

SEGG/

Display output segment G/

VSEL

10

15

BAT

ALARM

Audio alarm output

FAST

11

14

SNS

QDSEL

charge status display select

DCMD

12

13

TCO

24-Pin Narrow DIP

TM

Timer mode select

SEGF/

Display output segment F/

or SOIC

VSEL

Voltage termination select

MULT

multi-cell pack select

PN200701.eps

FAST

Fast charge rate select

SEGE/

Display output segment E/

DSEL2

display select 2

Discharge command

DCMD

SEGD/

Display output segment D/

TCO

Temperature cutoff

DSEL1

display select 1

9/96 B

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bq2007

The acceptable battery temperature range is set by an internal low-temperature threshold and an external high-temperature cutoff threshold. The absolute temperature is monitored as a voltage on the TS pin with the external thermistor network shown in Figure 2.

The bq2007 provides for undervoltage battery protection from high-current charging if the battery voltage is less than the normal end-of-discharge value. In the case of a deeply discharged battery, the bq2007 enters the charge-pending state and attempts trickle-current conditioning of the battery until the voltage increases. Should the battery voltage fail to increase above the discharge value during the undervoltage time-out period, a fault condition is indicated.

Discharge-before-charge may be selected to automatically discharge the battery pack on battery insertion or with a push-button switch. Discharge-before-charge on demand provides conditioning services that are useful to correct or prevent the NiCd voltage depression, or “memory” effect, and also provide a zero capacity reference for accurate capacity monitoring.

After prequalification and any required discharge- before-charge operations, charge action begins until one of the full-charge termination conditions is detected. The bq2007 terminates charging by any of the following methods:

Negative delta voltage (-∆V)

Peak voltage detect (PVD)

Maximum absolute temperature

Maximum battery voltage

Maximum charge time-out

The bq2007 may be programmed for negative delta voltage (-∆V) or peak voltage detect (PVD) charge termination algorithms. The VSEL input pin selects -∆V or PVD termination to match the charge rate and battery characteristics.

To provide maximum safety for battery and system, charging terminates based on maximum temperature cutoff (TCO), maximum cutoff voltage (MCV), and maximum time-out (MTO). The TCO threshold is the maximum battery temperature limit for charging. TCO terminates charge action when the temperature sense input voltage on the TS pin drops below the TCO pin voltage threshold. MCV provides battery overvoltage protection by detecting when the battery cell voltage (VCELL = VBAT - VSNS) exceeds the VMCV value and terminates fast charge, standard charge, or top-off charge. The maximum time-out (MTO) termination occurs when the charger safety timer has completed during the active charge state.

The bq2007 indicates charge state status with an audio alarm output option and two dedicated output pins with programmable display options. The DSEL1–2 inputs can select one of the three display modes for the LED1–2 outputs.

Charger status is indicated for:

Charge pending

Charge in progress

Charge complete

Fault condition

Pin Descriptions

SEGA–G Display output segments A–G

State-of-charge monitoring outputs. QDSEL input selects the bargraph or BCD digit display mode. See Table 3.

MSEL		Display driver mode select
		Soft-programmed input selects LED or LCD
		driver configuration at initialization. When
		MSEL is pulled up to VCC, outputs SEGA–G are
		LED interface levels; when MSEL is pulled
		down to VSS, outputs SEGA–G are LCD levels.
DSEL1–		Display mode select 1–2
DSEL2		Soft-programmed inputs control the LED1—2
		charger status display modes at initialization.
		See Table 2.
MULT		Fixed-cell pack select
		Soft-programmed input is pulled up to VCC
		when charging multi-cell packs and is pulled
		down to VSS for charging packs with a fixed
		number of cells.
QDSEL		State-of-charge display select
		The QDSEL input controls the SEGA–G
		state-of-charge display modes. See Table 3.
LED1–		Charger status outputs 1–2
LED2		Charger status output drivers for direct
		drive of LED displays. Display modes are
		selected by the DSEL input. See Table 2.
		Charge inhibit input
INH
		When low, the bq2007 suspends all charge ac-
		tions, drives all outputs to high impedance, and
		assumes a low-power operational state. When
		transitioning from low to high, a charge
		cycle is initiated. See page 10 for details.

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bq2007

COM Common LCD/LED output

Common output for LCD/LED display SEGA—G. Output is high-impedance during initialization to allow reading of soft-programmed inputs DSEL1, DSEL2, MSEL, MULT, and QDSEL.

ALARM		Audio output
		Audio alarm output.
TM		Timer mode select
		TM is a three-level input that controls the set-
		tings for charge control functions. See Table 5.
VSEL		Voltage termination select
		This input switches the voltage detect
		sensitivity. See Table 5.
FAST		Fast charge rate select
		The FAST input switches between Fast and
		Standard charge rates. See Table 4.
		Discharge command
DCMD
		The		input controls the discharge-
			DCMD
		before-charge function. A negative-going
		pulse initiates a discharge action. If DCMD
		is connected to VSS, automatic discharge-
		before-charge is enabled. See Figure 3.
TCO		Temperature cut-off threshold input
		Minimum allowable battery temperature-
		sensor voltage. If the potential between TS
		and SNS is less than the voltage at the TCO
		input, then any fast charging or top-off
		charging is terminated.
SNS		Sense resistor input
		SNS controls the switching of MOD output based
		on an external sense resistor. This provides the
		lower reference potential for the BAT pin and the
		TS pin.
BAT		Battery voltage input
		Battery voltage sense input referenced to SNS
		for the battery pack being charged. This resis-
		tor divider network is connected between the
		positive and the negative terminals of the
		battery. See Figure 1.

TS	Temperature sense input
	Input referenced to SNS for battery tem-
	perature monitoring negative temperature
	coefficient (NTC) thermistor.

DIS	Discharge control
	DIS is a push-pull output that controls an
	external transistor to discharge the battery
	before charging.
VSS	Ground
VCC	VCC supply input
MOD	Current-switching control output
	Push/pull output that controls the charging
	current to the battery. MOD switches high to
	enable current flow and low to inhibit current
	flow.

Functional Description

Figure 1 illustrates charge control and display status during a bq2007 charge cycle. Table 1 summarizes the bq2007 operational features. The charge action states and control outputs are given for possible input conditions.

Charge Action Control

The bq2007 charge action is controlled by input pins DCMD, VSEL, FAST, and TM. When charge action is initiated, the bq2007 enters the charge-pending state, checks for acceptable battery voltage and temperature, and performs any required discharge-before-charge operations. DCMD controls the discharge-before-charge function, and VSEL, FAST, and TM select the charger configuration. See Tables 4 and 5.

During charging, the bq2007 continuously tests for charge termination conditions: negative delta voltage, peak voltage detection, maximum time-out, battery over-voltage, and high-temperature cutoff. When the charge state is terminated, a trickle charge continues to compensate for self-discharge and maintain the fully charged condition.

Charge Status Indication

Table 2 summarizes the bq2007 charge status display indications. The charge status indicators include the DIS output, which can be used to indicate the discharge state, the audio ALARM output, which indicates charge completion and fault conditions, and the dedicated status outputs, LED1 and LED2.

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bq2007

Charge

Dis-

Fast Charging

Top-Off

Pulse-Trickle

Pending

charge

(Optional)

(Pulse-Trickle)

(Optional)

DIS

MOD

(Switching

260 s

Note

Configuration)

2080 s

260 s

or

(External

260 s

Note

MOD

Regulation)

Mode 1, LED2 Status Output

2080 s

260 s

Mode 1, LED1 Status Output

Mode 2, LED2 Status Output

Mode 2, LED1 Status Output

Mode 3, LED2 Status Output

Mode 3, LED1 Status Output

Battery discharged to VEDV or battery within temperature/voltage limits. (Discharge-before-charge not qualified by temperature.)

Low-voltage fault: Battery voltage less than VEDV for under-voltage time-out. Charge initiated. Battery outside temperature/voltage limits.

Note: See Table 4 for pulse-trickle period.

TD200701.eps

Figure 1. Example Charging Action Events

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bq2007

Outputs LED1–2 have three display modes that are selected at initialization by the input pins DSEL1 and DSEL2. The DSEL1 and DSEL2 input pins, when pulled down to VSS, are intended for implementation of a simple two-LED system. LED2 indicates the precharge status (i.e., charge pending and discharge) and LED1 indicates the charge status (i.e., charging and completion). DSEL1 pulled up to VCC and DSEL2 pulled down to VSS mode is for implementation of a single tri-color LED such that discharge, charging, and completion each have a unique color. DSEL1 pulled down to VSS and DSEL2 pulled up to VCC allows for fault status information to be displayed.

Audio Output Alarm

The bq2007 audio alarm output generates an audio tone to indicate a charge completion or fault condition. The audio alarm output is a symmetrical duty-cycle AC signal that is compatible with standard piezoelectric alarm elements. A valid battery insertion is indicated by a single high-tone beep of 12-second typical duration. The charge completion and fault conditions are indicated by a 9.5- to 15-second high-tone sequence of 12-second typical duration at a 2-second typical repetition rate.

Charge Status Monitoring

The bq2007 charge status monitor may display the battery voltage or charge safety timer as a percentage of the full-charged condition. These options are selected with the MULT soft-programmed input pin.

When MULT is pulled down to VSS, the battery charge status is displayed as a percentage of the battery voltage, and the single-cell battery voltage at the BAT pin is compared with internal charge voltage reference thresholds. When VBAT is greater than the internal thresholds of V20, V40, V60, or V80, the respective 20%, 40%, 60%, or 80% display outputs are activated. The battery voltage directly indicates 20% charge increments, while the 10% charge increments use a timer that is a function of the charge safety timer.

When MULT is pulled down to VSS and when VBAT exceeds V20 during charging, the 20% charge indication is activated and the timer begins counting for a period equal to 164 to 132 of the charge safety time-out period. When the timer count is completed, the 30% charge indication is activated. Should VBAT exceed V40 prior to the timer count completion, the charge status monitor activates the 30% and 40% indications. This technique

Table 1. bq2007 Operational Summary

	Charge Action
	State			Conditions	MOD Output	DIS Output
	Battery absent			VCC applied and VCELL ≥ VMCV	Trickle charge per Table 4	Low
	Charge initiation			VCC applied or VCELL drops	-	Low
				from ≥ VMCV to < VMCV
	Discharge-before-			high-to-low transition or to VSS on charge
			DCMD		Low	High
	charge		initiation and VEDV < VCELL < VMCV
	Charge pending		Charge initiation occurred and VTEMP ≥ VLTF or		Trickle charge per Table 4	Low
				VTEMP ≤ VTCO or VCELL < VEDV
	Fast charging		Charge pending complete and FAST = VCC		Low if VSNS > 250mV;	Low
					high if VSNS < 200mV
	Standard charging		Charge pending complete and FAST = VSS		Low if VSNS > 250mV;	Low
					high if VSNS < 200mV
	Charge complete		-∆V termination or VTEMP < VTCO or PVD ≥ 0 to		-	-
		-3mV/cell or maximum time-out or VCELL > VMCV
	Top-off pending		VSEL = VCC, charge complete and VTEMP ≥ VLTF		Trickle charge per Table 4	Low
				or VTEMP ≤ VTCO or VCELL < VEDV
			VSEL = VCC and charge complete and		Activated per VSNS for
	Top-off charging		time-out not exceeded and VTEMP > VTCO and			Low
				VCELL < VMCV	73ms of every 585ms
	Trickle charging		Charge complete and top-off disabled or		Trickle charge per Table 4	Low
				top-off complete or pending
	Fault		Charge pending state and charge pending		Trickle charge per Table 4	Low
				time-out (tPEND) complete

Definitions: VCELL = VBAT - VSNS; VMCV = 0.8 * VCC; VEDV = 0.262 * VCC or 0.4 * VCC; VTEMP = VTS - VSNS; VLTF = 0.5 * VCC.

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