L6206N datasheet(9/23 Pages) STMICROELECTRONICS

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L6206

NON-DISSIPATIVE OVERCURRENT DETECTION AND PROTECTION

In addition to the PWM current control, an overcurrent detection circuit (OCD) is integrated. This circuit can be

used to provides protection against a short circuit to ground or between two phases of the bridge as well as a

roughly regulation of the load current. With this internal over current detection, the external current sense resis-

tor normally used and its associated power dissipation are eliminated. Fig. 7 shows a simplified schematic of

the overcurrent detection circuit for the Bridge A. Bridge B is provided of an analogous circuit.

To implement the over current detection, a sensing element that delivers a small but precise fraction of the out-

put current is implemented with each high side power MOS. Since this current is a small fraction of the output

current there is very little additional power dissipation. This current is compared with an internal reference cur-

rent IREF. When the output current reaches the detection threshold Isover the OCD comparator signals a fault

condition. When a fault condition is detected, an internal open drain MOS with a pull down capability of 4mA

connected to OCD pin is turned on. Fig. 8 shows the OCD operation.

This signal can be used to regulate the output current simply by connecting the OCD pin to EN pin and adding

an external R-C as shown in Fig.7. The off time before recovering normal operation can be easily programmed

by means of the accurate thresholds of the logic inputs.

IREF and, therefore, the output current detection threshold are selectable by RCL value, following the equations:

– Isover = 5.6A ±30% at -25°C < Tj < 125°C if RCL = 0Ω (PROGCL connected to GND)

– Isover =

±10% at -25°C < Tj < 125°C if 5KΩ < RCL < 40kΩ

Fig. 9 shows the output current protection threshold versus RCL value in the range 5kΩ to 40kΩ.

The Disable Time tDISABLE before recovering normal operation can be easily programmed by means of the accu-

rate thresholds of the logic inputs. It is affected whether by CEN and REN values and its magnitude is reported in

Figure 10. The Delay Time tDELAY before turning off the bridge when an overcurrent has been detected depends

only by CEN value. Its magnitude is reported in Figure 11.

CEN is also used for providing immunity to pin EN against fast transient noises. Therefore the value of CEN should

be chosen as big as possible according to the maximum tolerable Delay Time and the REN value should be chosen

according to the desired Disable Time.

The resistor REN should be chosen in the range from 2.2KΩ to 180KΩ. Recommended values for REN and CEN

are respectively 100K

Ω and 5.6nF that allow obtaining 200µs Disable Time.

22100

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