STCMB1 datasheet(6/59 Pages) STMICROELECTRONICS

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Pin connections and description

STCMB1

6/59

DocID028958 Rev 4

Pin connections and description

Figure 3. Pin connections, top view

Table 1. Pin description

no.

Name

Function

1HV

High voltage start-up generator / ac voltage sensing input. The pin, able to withstand 800 V, has

to be connected to the ac side of the input bridge via a pair of diodes (1N400x type) to sense

the ac input voltage.

If the voltage on the pin is higher than 20 V (typical value), an internal pull-up circuit charges the

capacitor connected between the VCC pin and GND. Initially the current is low for safety in

case of a shorted VCC, and then it goes to the normal level as far as the VCC pin reaches the

start-up threshold. To reduce the hold-up requirement on the VCC cap, the generator is turned

off when the half-bridge section starts up. In case of a fault that prevents the half-bridge from

starting up, the HV generator is shut down after a timeout of 80 ms.

The generator is re-enabled when the voltage on the VCC pin falls below the UVLO threshold.

In case of a latched shutdown, when the VCC cycles between the start-up threshold and the

UVLO threshold, the current is reduced to keep power dissipation low. The same occurs in

case of a restart after a fault to create a longer restart delay.

The pin is used also to sense the ac voltage, which is used by the input voltage feedforward

and the ac brown-out functions. When a brown-out condition is detected any latched protection

converging on the FB pin is cleared.

An internal logic circuit detects that the unit has been detached from the power line and

activates the high voltage start-up generator to discharge the X-capacitors of the EMI filter to

a safe level. This allows the unit to meet safety regulations (such as IEC 61010-1 or

IEC 62368-1) without using the traditional discharge resistor in parallel to the X-capacitor, thus

saving the associated power losses and enabling ultra-low consumption in standby conditions.

A series resistor between 3 k

 and 9 k has to be mandatorily inserted in series to the pin.

N.C.

High voltage spacer. These pins are not internally connected to isolate the high voltage

sections and ease compliance with safety regulations (creepage distance) on the PCB.

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