ADP3810/ADP3811

–6–

REV. 0

240

120

0

5.0 5.2 5.4 5.6 5.8 6.0 6.2 6.4 6.6 6.8 7.0

200

160

80

40

Distribution

APPLICATIONS SECTION

Functional Description

The ADP3810 and ADP3811 are designed for charging NiCad,

NiMH and LiIon batteries. Both parts provide accurate voltage

sense and current sense circuitry to control the charge current

and final battery voltage. Figure 1 shows a simplified battery

charging circuit with the ADP3810/ADP3811 controlling an

external dc-dc converter. The converter can be one of many

different types such as a Buck converter, Flyback converter or a

linear regulator. In all cases, the ADP3810/ADP3811 maintains

accurate control of the current and voltage loops, enabling the

use of a low cost, industry standard dc-dc converter without

compromising system performance. Detailed realizations of

complete circuits including the dc-dc converter are included

later in this data sheet.

The ADP3810 and ADP3811 contain the following blocks

(shown in Figure 1):

• Two “GM” type error amplifiers control the current loop

(GM1) and the voltage loop (GM2).

• A common COMP node is shared by both GM amplifiers

such that an RC network at this node helps compensate both

control loops.

• A precision 2.0 V reference is used internally and is available

externally for use by other circuitry. The 0.1

µF bypass ca-

pacitor shown is required for stability.

• A current limited buffer stage (GM3) provides a current out-

put can directly drive an optocoupler in isolated converter

applications. The dc-dc converter must have a control scheme

not the case, a simple, single transistor inverter can be used

for control phase inversion.

• An amplifier buffers the charge current programming volt-

• An UVLO circuit shuts down the GM amplifiers and the

protects the charging system from indeterminate operation.

when the voltage on the “+” input of GM2 rises over 120 mV

quickly recover from overvoltage transients and protect ex-

ternal circuitry.

Description of Battery Charging Operation

The IC based system shown in Figure 1 charges a battery with a

dc current supplied by a dc-dc converter, which is most likely a

switching type supply but could also be a linear supply where

feasible. The value of the charge current is controlled by the

formula below:

1

×

R3

80 k

Ω

×V

CTRL

Ω and R3 = 20 kΩ, which result

in a charge current of 1.0 A for a control voltage of 1.0 V. The

80 k

Ω resistor is internal to the IC, and it is trimmed to its ab-

solute value. The positive input of GM1 is referenced to

Ω) V

grammed level (i.e., the charge current increases), the negative

input of GM1 goes slightly below ground. This causes the out-

put of GM1 to source more current and drive the COMP node

decreases the drive to the dc-dc converter, reducing the charg-

ing current and balancing the feedback loop.

As the battery approaches its final charge voltage, the voltage

loop takes over. The system becomes a voltage source, floating

the battery at constant voltage thereby preventing overcharging.

The constant voltage feature also protects the circuitry that is

actually powered by the battery from overvoltage if the battery is

removed. The voltage loop is comprised of R1, R2, GM2 and

the dc-dc converter. The final battery voltage is simply set by

the ratio of R1 and R2 according to the following equation

R1

R2

+1









If the battery voltage rises above its programmed voltage,

8

7

3

03

18

6

9

12

15

6

5

4

TEMPERATURE –

°C

0.25

0.20

0

–50

–25

100

025

50

75

0.15

0.10

0.05