ADP3801 datasheet(16/20 Pages) AD

16 / 20 page

ADP3801/ADP3802

–16–

REV. 0

NiCad/NiMH Charging

When paired with a low cost, 8-bit microcontroller, the

ADP3801/ADP3802 charges NiCad and NiMH batteries. The

ADP3801/ADP3802 is used to provide a programmable charge

current limit with a fail-safe voltage limit, and the microcontroller

monitors the battery and determines the charge termination.

Common methods for termination are “negative delta V” and

“delta T.” Both methods require that the present value of either

the voltage or temperature be compared to a previous value.

Such functionality is performed by an

µC with an on-board

ADC.

The

µC and the ADP3801/ADP3802 are configured as shown

in Figure 30 for the universal charger. The voltage setting on the

ADP3801/ADP3802 should not interfere with normal charging,

but still provide a fail safe voltage if the battery is removed. For

example, if a 6-cell NiCad battery is being charged, the output

voltage of the ADP3801/ADP3802 should be programmed to

12.6 V. The 6-cell battery has a peak voltage of approximately

1.7 V–1.8 V per cell, giving a total voltage of 9.6 V–10.8 V.

Thus, the 12.6 V setting provides enough headroom for normal

charging.

Universal Battery Charger

The combination of a

µC and the ADP3801/ADP3802 can be

extended to a low cost universal charger for Li-Ion and NiCad/

NiMH as shown in Figure 30. The

µC with on-board A/D con-

verter monitors the battery’s voltage and temperature to deter-

mine the end-of-charge for either NiCad or NiMH batteries.

The ADP3801/ADP3802 also monitors the battery voltage to

determine the end-of-charge for Li-Ion. The EOC output is

connected to a digital input on the

µC for signaling. The µC can

shutdown the charger circuitry when it is not required. The

µC

shown operates from 3.3 V, so it can be powered directly from

the LDO of the ADP3801/ADP3802. The LDO voltage also

serves as a 1% reference for the

µC’s ADC.

VCC

ISET

BATA

GND

PROG

EOC

ADP3801/

ADP3802

CHARGER CIRCUIT

PA1

PA0

AN1

AN0

PA2

PA3

VDD

VIN

MICRO-

CONTROLLER

T = BATTERY

THERMISTOR

Figure 30. Universal Battery Charger Block Diagram

Both the charge current and the final battery voltage can be

dynamically set by using a PWM output from the

µC. The PWM

inputs to ISET and PROG are filtered by an RC combination to

generate a dc voltage on the pins. This functionality allows

multiple battery types and chemistries to be accommodated in a

single charger circuit.

Dual Li-Ion Battery Charger

Some applications such as certain desktop chargers for cellular

phones or laptops with two batteries require that two separate

battery stacks be charged independently. The ADP3801/ADP3802

is designed to handle these applications with two battery sense

inputs and a multiplexer to select between the two. The applica-

tion circuit is essentially the same as Figure 24 except that exter-

nal FETs must be added to direct the charge current to the

proper battery stack. Figure 31 shows the additional circuitry

needed.

Si4463

4.3k

BATA

BATB

A/B

CS–

CS+

4.3k

ADP3801/

ADP3802

RCS

40m

100k

Si4463

MBRD835

BATA

BATB

A/B

SELECTOR

* OPEN-COLLECTOR OUTPUTS

MBRD835

Figure 31. Dual Li-Ion Battery Charger

To provide alternate or sequential charging, the two separate

batteries are alternately connected to the output of the charger

by two Si4463 PFETs. The control of these FETs is accom-

plished by open-collector logic outputs and 100 k

Ω pull-up

resistors. The programming of the A/B terminal should come

from a 0 V to 3.3 V logic output. Most likely a dedicated logic

circuit or a microcontroller would control the system. The

BATB sense input is enabled by connecting a >2 V potential to

the A/B input (or <0.8 V to select BATA). The A and B battery

voltages are directly sensed by the BATA and BATB inputs.

Two Schottky diodes are also included to prevent one battery

stack from shorting to the other through the body diodes of the

FETs. When the charger has finished charging one battery (sig-

naled by the EOC output), the MUX and external FETs can be

switched to charge the second battery. When switching from

one battery to the next the following procedure is recommended

to minimize transient currents:

1. Turn off the ADP3801/ADP3802 PWM by bringing the SD

pin low.

2. Turn off the FET to the battery being charged.

3. Wait approximately 60 seconds for CO to discharge through

RB.

4. Turn on the FET to the second battery.

5. Change the A/B SELECT MUX to the second battery.

6. Turn on the ADP3801/ADP3802 by bringing the SD pin

high.

ADP3801 Datasheet(PDF) 16 Page - Analog Devices

ADP3801 Datasheet(HTML) 16 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Datasheet Download

Link URL