AN1283 - APPLICATION NOTE

2/7

3 - CALCULATION OF THE ELEMENTS

The charge current is regulated at 700mA (if the

charge control input is left open) or 200mA (if the

charge control input is put to ground ), allowing the

charge of two different types of batteries.

3.1 Voltage limitation

The end-of-charge voltage is limited at 1.45V/cell,

this is the recommended voltage for an ambient

temperature at 25°C.

A diode is generally inserted at the output of the

charger to avoid the discharge of the battery if the

charger is not powered. This diode is sometimes

directly integrated in the battery pack. The

influence of this diode on the charge is negligible if

the voltage drop (0.7V) is taken into account

during the design of the charger.

The voltage at the output of the charger is :

in this equation)

The following values are used on the application

board :

battery replaced by a 1k

Ω resistor

3.2 Current regulation

measurement.

The current regulation is effective when the

pin 5 of the TSM101 (assuming that the internal

current source is disabled).

For medium currents (<1A), a voltage drop across

realized with standard low cost 0.5W resistors in

parallel.

(four 1.2

Ω resistor in parallel)

formula :

3.3 Charge control

If the pin 2 is left open, the charge current is

nominal at 700mA.

If pin 2 is connected to ground, the internal current

source is enabled, the current measurement is

offset by a voltage equal to :

This can be used to lower the charging current or

In our example, the current offset is equal to 700 -

200mA = 500mA, representing a voltage offset

The following values are used on the application

board :

parallel)

4 - SCHEMATIC DIAGRAM

Figure 2 represents a schematic of the output

circuit of a “classical” SMPS using a TL431 for

voltage regulation. This circuit is modified to use

the TSM101 and the final circuit is represented in

Figure 3.

V

OU T

R

6

R

7

+

R

6

--------------------- V

ref

⋅

=

R

6

V

ref

V

out

V

ref

+

----------------------------- R

7

⋅

=

R

5

V

R

5

I

ch

----------

0.285

Ω

==

R

6

R

3

V

ref

V

R

5

–

V

R

5

---------------------------

⋅

=

V

R

4

I

⋅

=