DESCRIPCIÓN

The TSM101/TSM101A integrated circuit incorporates a high stability series band gap voltage reference, two ORed operational amplifiers and a current source.
This IC compares the DC voltage and the current level at the output of a switching power supply to an internal reference. It provides a feedback through an optocoupler to the PWM controller IC in the primary side.
The controlled current generator can be used to modify the level of current limitation by offsetting the information coming from the current sensing resistor.

 

APLICACIONES

This circuit is designed to be used in battery chargers with a constant voltage and a limited out put current.
It can be used in every types of application requiring a precision voltage regulation and current limitation.
Other applications include voltage supervisors, over voltage protection.

 

TSM101 PRESENTATION

The TSM101 integrated circuit incorporates a high stability series band gap voltage reference, two ORed operational amplifiers and a current source.
This IC compares the DC voltage and the current level at the output of a switching power supply to an internal reference.It provides a feedback through an optocoupler to the PWM controller IC in the primary side.
The controlled current generator can be used to modify the level of current limitation by offsetting the information coming from the current sensing resistor.
A great majority of low or medium end power supplies is voltage regulated by using shunt programmable voltage references like the TL431.
The galvanic insulation of the control information is done by using an opto-coupler in linear mode with a variable photo current depending on the difference between the actual output voltage and the desired one.
A current limitation is used to protect the power supply against short circuits, but lacks precision.This limitation is generally realized by sensing the current of the power transistor, in the primary side of the SMPS.
The role of the TSM101 is to make a fine regulation of the output current of the SMPS and a precise voltage limitation.
The primary current limitation is conserved and acts as a security for a fail-safe operation if a short-circuit occurs at the output of the charger.

 

PRINCIPLE OF OPERATION

The current regulation loop and the voltage limitation loop use an internal 1.24V band-gap voltage reference. This voltage reference has a good precision (better than 1.5%) and exhibits a very stable temperature behavior.
The optocoupler current increases and tends to reduce the output voltage by the way of the PWM controller.
If this part is higher than 1.24V, the output of the voltage loop operational amplifier decreases.
The optocoupler current increases and tends to reduce the output voltage by the way of the PWM controller.
By enabling the TSM101 current source (pin 2) it is possible to offset the current sensing by a voltage equal to :
Voff # R4 * Io with Io = 1.4mA
This offset lowers the output charge current and this function can be used to charge two types of batteries having different capacities. The current source is enabled by connecting pin 2 to ground.

 

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.

 

Higher Precision for the Voltage Control

The voltage drop through the sense resistor R5 offsets the voltage measurement. In most battery charging applications, this offset is not taken into account because the error is negligeable compared to the end-of-charge voltage due to the fact that the charging current value decreases drastically during the final phase of the battery charging.But in other applications needing highest possible precision in voltage control.
The following application includes a specific recommendation which requires that the charging current should be fixed to Ich1 = 800mA in normal charging conditions, and Ich2 = 200mA when the cell voltage is below Vl=2.5V to optimize the cell life-time.