TSM105

6/9

An example of a suitable compensation network is

shown in Fig.2. It consists of a capacitor

Cvc1=2.2nF and a resistor Rcv1=470K

Ω in series,

connected in parallel with another capacitor

Cvc2=22pF.

The current-control trans-conductance operation-

al amplifier has to be compensated in a different

way, since its negative input is connected to

ground. A series connection of a capacitor

Cic1=100nF and a resistor Ric1=22

Ω can be put

between OUT and GND to stabilize the global reg-

ulation loop.

3. Start Up and Short Circuit Conditions

Under start-up or short-circuit conditions the

TSM105 is not provided with a high enough supply

voltage. This is due to the fact that the chip has its

power supply line in common with the power sup-

ply line of the system.

Therefore, the current limitation can only be en-

sured by the primary PWM module, which should

be chosen accordingly.

If the primary current limitation is considered not to

be precise enough for the application, then a suffi-

cient supply for the TSM105 has to be ensured un-

der any condition. It would then be necessary to

add some circuitry to supply the chip with a sepa-

rate power line. This can be achieved in numer-

ous ways, including an additional winding on the

transformer.

The following schematic shows how to realise a

low-cost power supply for the TSM105 (with no

additional windings).

Please pay attention to the fact that in the particu-

lar case presented here, this low-cost power sup-

ply can reach voltages as high as twice the volt-

age of the regulated line. Since the Absolute Max-

imum Rating of the TSM105 supply voltage is 14

V, this low-cost auxiliary power supply can only be

used in applications where the regulated line volt-

age does not exceed 7 V.

Figure 4 :

+

-

+

-

1.210V

200mV

Vcc

Out

Vctrl

Gnd

Ictrl

D

+

CS

R2

R1

Rsense

Rvc1

470K

Cvc1

2.2nF

Ric1

22

To primary

OUT+

OUT-

+

TSM105

Cic1

100nF

Cvc2

22pF

IL

IL

Vsense

DS

+

Rs

Vcc