Philips SAA1501T-N3 Datasheet

DATA SH EET

Objective speciﬁcation File under Integrated Circuits, IC11

December 1994

INTEGRATED CIRCUITS

Philips Semiconductors

SAA1501T

Battery charge level indicator

December 1994 2

Philips Semiconductors Objective speciﬁcation

Battery charge level indicator SAA1501T

FEATURES

• High level of integration to allow assembly in intelligent battery packs

• Accurate charge and discharge account

• Large dynamic range of charge and discharge currents

• Independent settings of charge and discharge efficiency

• 2 V minimum supply voltage (2 cell operation)

• Temperature protection of batteries during charging

• Temperature controlled self-discharge

• Accurate charge current regulation

• Two charge amount display modes, LCD and LED.

GENERAL DESCRIPTION

The SAA1501T is intended to be used as a battery monitor and charge current control circuit in rechargeable battery systems.

The SAA1501T is processed in BiCMOS technology where the benefits of mixed bipolar and CMOS technology is fully utilized to achieve high accuracy measurements and digital signal processing in the same device. The general function of the integrated circuit is a Coulomb counter. During battery charging, the charge current and charge time are registered in a Coulomb counter. During discharge, the discharge current and time are recorded. The momentary charge amount of the batteries can be displayed either on an LCD screen or on an LED bargraph. Using the SAA1501T, intelligent batteries or intelligent battery powered systems can be easily designed with only a few external components.

QUICK REFERENCE DATA

ORDERING INFORMATION

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT

supply voltage 2.0 3.0 4.3 V

supply current VCC=3V;

Ic=Id=60µA

− 1.2 1.7 mA

CCstb

supply current in standby mode VCC=3 V;

CSI=VDSI

=0V

−− 100 µA

osc

ﬁxed oscillator frequency C

osc

= 820 pF;

ref

= 51.5 kΩ

− 4.2 − kHz

i(s)

input sense voltage (pins 9 and 10) 0 − VCC− 1.6 V

amb

operating ambient temperature 0 − +70 °C

TYPE NUMBER

PACKAGE

NAME DESCRIPTION VERSION

SAA1501T SO24 plastic small outline package; 24 leads; body width 7.5 mm SOT137-1

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Philips Semiconductors Objective speciﬁcation

Battery charge level indicator SAA1501T

BBB

BBBB

BBB

BBBB

BBB

B B B

B B

BBBBBB

BBBBBBB

B B B

B B

BBB B

BBB

BLOCK DIAGRAM

Fig.1 Block diagram.

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Philips Semiconductors Objective speciﬁcation

Battery charge level indicator SAA1501T

PINNING

SYMBOL PIN DESCRIPTION

1 supply voltage EN 2 enable output C

3 duty cycle capacitor output C

4 charge counter capacitor output I

5 maximum average charge current

setting input

ref

6 current reference resistor input R

DCC

7 discharge current conversion resistor

input

CCC

8 charge current conversion resistor

input CSI 9 charge sense input DSI 10 discharge sense input R

TEMP1

11 temperature sensing resistor 1 input

TEMP2

12 temperature sensing resistor2 input

osc

13 oscillator capacitor input BUZ 14 buzzer output FULL 15 battery full indication output L100 16 100% segment indication output L80 17 80% segment indication output L60 18 60% segment indication output L40 19 40% segment indication output L20 20 20% segment indication output BP 21 LCD back plane drive BLI 22 battery low indicator LED output POL 23 power-on LED output GND 24 power ground

Fig.2 Pin configuration.

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Philips Semiconductors Objective speciﬁcation

Battery charge level indicator SAA1501T

FUNCTIONAL DESCRIPTION

The most important function of the SAA1501T is the charge account in rechargeable battery systems. Both NiCd and NiMH batteries in all sizes can be used. The system can operate alone as a charge monitor with a charge amount display function or, can operate in conjunction with a charger. If the SAA1501T operates together with a charger, it delivers a control signal at output EN, for charge current regulation or for battery voltage regulation.

Fast charging systems and charge current regulation

The SAA1501T is especially designed to be used in fast charging systems. In fast charging systems, the charge time is lowered by raising the charge current. Signal EN controls the charger current. The counters register the state of charge of the batteries and at the 80% level the charge current is reduced via a smaller duty cycle regulation of signal EN. The second (slow) level fully charges the batteries which is not possible with the first (fast) level. After the slow charge mode the counter switches over to an even smaller duty cycle of EN and thus enters the third (trickle) charge mode, to overcome the self-discharge of the batteries.

Current sensing and charge account

The charge current is sensed by means of a very low resistance (e.g. 70 mΩ) sense resistor R

(see Fig.8) to save power at high charge rates. Via the V/I charge converter and external resistor R

CCC

(see Fig.8), the sensed voltage is converted into a charge current Ic (the same is applicable for the discharge current). In the I/F converter the charge current is converted into a frequency for up-counting the counter. For the discharge current (Id) the converted frequency is used for down-counting. The up and down counting is registered in counters CNT1 and CNT2, depending on the actual charge and discharge current levels of the batteries. This is called dynamic charge account.

Charge display

The charge amount represented by the Coulomb counter can be displayed via an LCD screen or via an LED bargraph. If the charge amount is reduced to 0%, the battery low indicator (BLI) LED is turned on at the end of a battery discharge session. A flashing BLI, in combination with a repeating buzzer alarm, informs the user about the low charge state. A new charge session should then be started.

Protections

In the temperature control block, the absolute temperature is used as a protection to end the fast charge cycle. Fast charging at high temperature is not permitted because of degradation of the battery cells. If the batteries are disconnected, an open-battery condition is recognized and the SAA1501T enters the standby mode.

Mode detection

The mode detector detects whether there are any charge or discharge currents, whether the system is powered, whether loads are connected or whether the system is in the standby mode. If power is connected, the power-on LED (POL) is on. In the standby mode, the Coulomb counter will count down in accordance with the self-discharge speed of the batteries, which is temperature controlled. The following subsections describe the various blocks of the block diagram in more detail.

Supply and reference

During the period when VCC rises from 0 V to the internal reset level, all counters are reset. The internal reset is released before VCC reaches 1.7 V. The operating supply voltage ranges from 2 V to the open battery level of

4.3 V (min). The characteristics are guaranteed at VCC= 3 V. In order to protect the SAA1501T against high supply voltages during open battery in a flyback converter, a voltage clamp circuit is made active at 6.35 V (typ). The clamping current must not exceed 80 mA. A band gap reference block is included to generate accurate voltages i.e. for the oscillator. Moreover, together with R

ref

, accurate currents are generated which are used in the I/F and V/I converters and the oscillator block. In the standby mode only the oscillator and the digital parts are active to limit the discharge current of the batteries to a current level of less than 100 mA. The circuits that are needed temporarily are switched on and off during standby (see “Timing characteristics” t

som

Voltage-to-current charge and discharge

In the V/I converter, the input charge current is translated into acceptable levels for the circuit. The conversion formula is:

; where R

CCC>Rsc

(see Fig.7)I

ch earg

Rsc×()

CCC

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Philips Semiconductors Objective speciﬁcation

Battery charge level indicator SAA1501T

With R

CCC

, the charge efficiency can be manipulated depending on the charge level. The restriction of the SAA1501T is a maximum average charge current of 60 µA and a minimum momentary charge current of 0.6 µA. The same formula is applicable for the discharge current. The discharge efficiency can now also be changed by R

DCC

depending on the discharge current levels, but independent of the charge current. As both sense levels are referenced to ground, the sensing elements could be combined into one. The outputs are used combined as

⁄6× (Ic− Id) in the I/F converter and combined as (Ic− Id) in the pulse width modulator block and made separately available in the mode detector. The conversion is made lower by a factor of 6 in the I/F converter block, thereby enabling the use of poor leakage capacitors on pin 4. All V/I converter pins are sensitive to capacitive loading (C

out

× R

conv

< 1 ms), the conversion resistors should be

mounted as close as possible to the output pins.

I/F converter

This block produces up-counts while charging and down-counts while discharging. The I/F converter translates the charge/discharge currents into a frequency. This frequency is determined by

During the time period ‘t’, the charge current, expressed as a ‘Charge Parcel’, will be counted in the Coulomb counters (CNT1 and CNT2). During discharge the ‘Charge Parcel’ is the product of the discharge current and the ‘t’ from the I/F converter generated frequency. The momentary contents of the Coulomb counter is a multiple of the ‘Charge Parcels’.

Coulomb counters CNT1 and CNT2

The SAA1501T has been designed for average maximum charge and discharge current levels of 5 C and minimum charge and discharge current levels of 0.05 C. This means that counter CNT1 will be full, or empty, after a minimum time period of 12 minutes at maximum charge and discharge currents at the recommended oscillator frequency. Higher charge and discharge rates than 5 C are possible, but only by changing the oscillator frequency. It should be noted that the self-discharge time and the display functions are influenced by a higher oscillator frequency. The SAA1501T enables top-up charging in order to account for the decrease of charge efficiency at high charge rates. The SAA1501T switches to the slow charge mode at full recognition when CNT1 is at its maximum. As soon as the batteries are completely full (when CNT2 is at its maximum), the SAA1501T switches

cd()Rsense

6 )××

∆V

oscRCCC RDCC()

)××

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to the trickle charge mode to overcome the self-discharge of the batteries. The top-up charge volume of CNT2 = 0.2 × CNT1 = 0.2 C (where Q is rated as Ampere hours of the battery). The slow and trickle charge current levels are dependent on the k-factor. Signal EN controls the external charger e.g. TEA1400 (see Fig.8). When an LED bargraph display is used, the LED currents are also considered as a battery discharge current, and therefore influence the duty cycle of the charge current regulation signal EN. The SAA1501T also enables temperature protection. In the event that the battery temperature exceeds a certain maximum temperature level (T

battery>Tmax

), which can be set by an external NTC resistor, the SAA1501T switches to the slow charge mode. In the standby mode (self-discharge mode), which is recognized by the SAA1501T in the mode detector when both the charge and discharge currents are zero (Ic=Id= 0), the self-discharge of the batteries is registered by counting down in 200 days (based on f

osc

= 4 kHz) if

battery<Tself

or in 100 days (based on f

osc

= 4 kHz) if

battery>Tself

. T

self

is also set by means of an external NTC

resistor.

Band gap generation

From the band gap voltage block, two reference voltages are derived V

ref

and V

max

. Voltage V

ref

at pin R

ref

sets the

reference currents, I

ref1

(I/F converter); I

ref2

(mode

detector) and I

ref3

(oscillator). Voltage V

max

sets the

current I

max

which is used in the pulse width modulation

block to accurately control the charge current.

Charge current regulation

While charging, the SAA1501T produces a charge current regulation signal EN in the pulse width modulation block which is used for controlling an external charger. This digital signal EN is derived from the signal produced at pin C

. The duty cycle is determined by

in which the value of k depends on the state of the counters CNT1 and CNT2:

CNT1 is not full; k = 1 (fast charging). CNT1 is full; CNT2 is not full; k = 0.1 (slow charging). CNT1 and CNT2 are full; k = 0.025 (trickle charging).

max

cId

–

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