Texas Instruments BQ2000TPN-B5, BQ2000TPN-B4, BQ2000TSN-B5TR, BQ2000TSN-B5, BQ2000TSN-B4TR Datasheet

Features

Safe management of fast charge for NiCd, NiMH, or LiIon battery packs

High-frequency switching controller for efficient and simple charger design

Pre-charge qualification for detecting shorted, damaged, or overheated cells

Fast-charge termination by ∆T/∆t minimum current (Li-Ion), maximum temperature, and maximum charge time

Selectable top-off mode for achieving maximum capacity in NiMH batteries

Programmable trickle-charge mode for reviving deeply discharged batteries and for postcharge maintenance

Built-in battery removal and insertion detection

Sleep mode for low power consumption

bq2000T

Programmable Multi-Chemistry

Fast-Charge Management IC

General Description

The bq2000T is a programmable, monolithic IC for fast-charge management of nickel cadmium (NiCd), nickel metal-hydride (NiMH), or lith- ium-ion (Li-Ion) batteries in singleor multi-chemistry applications. The bq2000T detects the battery chemistry and proceeds with the optimal charging and termination algorithms. This process eliminates undesirable undercharged or overcharged conditions and allows accurate and safe termination of fast charge.

Depending on the chemistry, the bq2000T provides a number of charge termination criteria:

Rate of temperature rise, ∆T/∆t (for NiCd and NiMH)

Minimum charging current (for Li-Ion)

Maximum temperature

Maximum charge time

For safety, the bq2000T inhibits fast charge until the battery voltage and temperature are within user-defined limits. If the battery voltage is below the low-voltage threshold, the bq2000T uses trickle-charge to condition the battery. For NiMH batteries, the bq2000T provides an optional top-off charge to maximize the battery capacity.

The integrated high-frequency comparator allows the bq2000T to be the basis for a complete, high-efficiency power-conversion circuit for both nickel-based and lithium-based chemistries.

Pin Connections

SNS		1	8	MOD
VSS		2	7	VCC
		3	6	RC
LED
BAT		4	5	TS

8-Pin DIP or Narrow SOIC or TSSOP

PN-2000.eps

SLUS149A–FEBRUARY 2000

Pin Names

	SNS		Current-sense input	TS	Temperature-sense
	VSS		System ground		input
				RC	Timer-program input
			Charge-status
	LED			VCC
			output		Supply-voltage input
	BAT		Battery-voltage	MOD	Modulation-control
			input		output

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bq2000T

Pin Descriptions

SNS	Current-sense input
	Enables the bq2000T to sense the battery
	current via the voltage developed on this pin
	by an external sense-resistor connected in
	series with the battery pack

VSS	System Ground
	Charge-status output
LED
	Open-drain output that indicates the charg-
	ing status by turning on, turning off, or
	flashing an external LED

BAT	Battery-voltage input
	Battery-voltage sense input. A simple resistive
	divider, across the battery terminals, generates
	this input.
TS	Temperature-sense input

RC	Timer-program input
	RC input used to program the maximum
	charge-time, hold-off period, and trickle
	rate during the charge cycle, and to disable
	or enable top-off charge

VCC	Supply-voltage input
MOD	Modulation-control output
	Push-pull output that controls the charging
	current to the battery. MOD switches high
	to enable charging current to flow and low to
	inhibit chargingcurrent flow.

Functional Description

The bq2000T is a versatile, multi-chemistry batterycharge control device. See Figure 1 for a functional block diagram and Figure 2 for the state diagram.

Input for an external battery-temperature monitoring circuit. An external resistive divider network with a negative tempera- ture-coefficient thermistor sets the lower and upper temperature thresholds.

				TS
		Voltage		Voltage
		Reference		Comparator
	BAT	ADC	∆T/∆t
			ALU
	OSC	Clock	Timer	Charge	LED
		Phase
				Control
		Generator
	RC
		Internal		Voltage	MOD
		OSC		Comparator
			SNS	VCC	VSS
					BD2000T.eps

Figure 1. Functional Block Diagram

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							bq2000T
				4.0V < VCC < 6.0V
				Charge
				Initialization
			VBAT < VSLP	Battery Voltage		VMCV < VBAT < VSLP
	Sleep
				(checked at all times)
	Mode
			VSLP < VBAT < VCC
				VBAT < VMCV
			VTS > VHTF
	Charge		VTS < VHTF	Battery Temperature
	Suspended			(checked at all times)
			VBAT < VLBAT or		VLBAT < VBAT < VMCV and
	Battery		VTS > VLTF		VHTF < VTS < VLTF		Current
	Conditioning					Regulation
			VLBAT < VBAT < VMCV and		∆T/∆t (after hold-off period),
			VHTF < VTS < VLTF		or VTS	< VTCO or	Time < MTO
					Time = MTO
							and
							VBAT > VMCV
VCC			No
Reset	Maintenance			Top-Off			Voltage
	Charge					Regulation
				Selected?
				Yes
							Current Taper
							or
							Time = MTO
		Time = MTO or			VBAT > VMCV
		VTS < VTCO		Top-Off
							Done
					VBAT > VMCV
			VCC Reset or Battery Replacement or Capacity Depletion (Li-Ion)
							SD2000T.eps

Figure 2. State Diagram

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bq2000T

Initiation and Charge Qualification

The bq2000T initiates a charge cycle when it detects

Application of power to VCC

Battery replacement

Exit from sleep mode

Capacity depletion (Li-Ion only)

Immediately following initiation, the IC enters a charge-qualification mode. The bq2000T charge qualification is based on battery voltage and temperature. If voltage on pin BAT is less than the internal threshold, VLBAT, the bq2000T enters the charge-pending state. This condition indicates the possiblility of a defective or shorted battery pack. In an attempt to revive a fully depleted pack, the bq2000T enables the MOD pin to trickle-charge at a rate of once every 1.0s. As explained in the section “Top-Off and Pulse-Trickle Charge,” the trickle pulse-width is user-selectable and is set by the value of the resistance connected to pin RC.

During this period, the LED pin blinks at a 1Hz rate, indicating the pending status of the charger.

Similarly, the bq2000T suspends fast charge if the battery temperature is outside the VLTF to VHTF range. (See Table 4.) For safety reasons, however, it disables the pulse trickle, in the case of a battery over-temperature condition (i.e., VTS < VHTF). Fast charge begins when the battery temperature and voltage are valid.

Battery Chemistry

The bq2000T detects the battery chemistry by monitoring the battery-voltage profile during fast charge. If the voltage on BAT input rises to the internal VMCV reference, the IC assumes a Li-Ion battery. Otherwise the bq2000T assumes NiCd/NiMH chemistry.

As shown in Figure 6, a resistor voltage-divider between the battery pack’s positive terminal and VSS scales the battery voltage measured at pin BAT. In a mixed-chemistry design, a common voltage-divider is used as long as the maximum charge voltage of the nickel-based pack is below that of the Li-Ion pack. Otherwise, different scaling is required.

Once the chemistry is determined, the bq2000T completes the fast charge with the appropriate charge algorithm (Table 1). The user can customize the algorithm by programming the device using an external resistor and a capacitor connected to the RC pin, as discussed in later sections.

NiCd and NiMH Batteries

Following qualification, the bq2000T fast-charges NiCd or NiMH batteries using a current-limited algorithm. During the fast-charge period, it monitors charge time, temperature, and voltage for adherence to the termination criteria. This monitoring is further explained in later sections. Following fast charge, the battery is topped off, if top-off is selected. The charging cycle ends

IMAX

Current

Trickle

IMIN

Qualification

VMCV

Voltage

Fast Charge

VLBAT

Phase 1		Phase 2
	Current	Voltage

Time

GR2000CA.eps

Figure 3. Lithium-Ion Charge Algorithm

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bq2000T

			Table 1. Charge Algorithm
	Battery Chemistry		Charge Algorithm
		1.	Charge qualification
		2.	Trickle charge, if required
	NiCd or NiMH	3.	Fast charge (constant current)
		4.	Charge termination (∆T/∆t, time)
		5.	Top-off (optional)
		6.	Trickle charge
		1.	Charge qualification
	Li-Ion	2.	Trickle charge, if required
		3.	Two-step fast charge (constant current followed by constant voltage)
		4.	Charge termination (minimum current, time)

with a trickle maintenance-charge that continues as long as the voltage on pin BAT remains below VMCV.

charge. This feature provides the additional charge time required for Li-Ion cells.

Lithium-Ion Batteries

The bq2000T uses a two-phase fast-charge algorithm for Li-Ion batteries (Figure 3). In phase one, the bq2000T regulates constant current until VBAT rises to VMCV. The bq2000T then moves to phase two, regulates the battery with constant voltage of VMCV, and terminates when the charging current falls below the IMIN threshold. A new charge cycle is started if the cell voltage falls below the VRCH threshold.

During the current-regulation phase, the bq2000T monitors charge time, battery temperature, and battery voltage for adherence to the termination criteria. During the final constant-voltage stage, in addition to the charge time and temperature, it monitors the charge current as a termination criterion. There is no post-charge maintenance mode for Li-Ion batteries.

Charge Termination

Maximum Charge Time (NiCD, NiMH, and

Li-Ion)

The bq2000T sets the maximum charge-time through pin RC. With the proper selection of external resistor and capacitor, various time-out values may be achieved. Figure 4 shows a typical connection.

The following equation shows the relationship between the RMTO and CMTO values and the maximum charge time (MTO) for the bq2000T:

MTO = RMTO CMTO 35,988

MTO is measured in minutes, RMTO in ohms, and CMTO in farads. (Note: RMTO and CMTO values also determine other features of the device. See Tables 2 and 3 for details.)

For Li-Ion cells, the bq2000T resets the MTO when the battery reaches the constant-voltage phase of the

Maximum Temperature (NiCd, NiMH, Li-Ion)

A negative-coefficient thermistor, referenced to VSS and placed in thermal contact with the battery, may be used as a temperature-sensing device. Figure 5 shows a typical temperature-sensing circuit.

During fast charge, the bq2000T compares the battery temperature to an internal high-temperature cutoff threshold, VTCO. As shown in Table 4, high-temperature termination occurs when voltage at pin TS is less than this threshold.

∆T/∆t (NiCd, NiMH)

When fast charging, the bq2000T monitors the voltage

at pin TS for rate of temperature change detection, ∆T/∆t. The bq2000T samples the voltage at the TS pin

every 16s and compares it to the value measured 2 samples earlier. This feature terminates fast charge if this voltage declines at a rate of

VCC V 161 Min

Figure 5 shows a typical connection diagram.

Minimum Current (Li-Ion Only)

The bq2000T monitors the charging current during the voltage-regulation phase of Li-Ion batteries. Fast charge is terminated when the current is tapered off to 7% of the maximum charging current. Please note that this threshold is different for the bq2000.

Initial Hold-Off Period

The values of the external resistor and capacitor connected to pin RC set the initial hold-off period. During this period, the bq2000T avoids early termination by disabling the ∆T/∆t feature. This period is fixed at the

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