AN1172 STMICROELECTRONICS | Alldatasheet
Document overview
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Technical content
Datasheet sections
- 1 ACS triggering mode
- 1.1 Negative gate current
- 1.2 New layout possibilities
- 2 Inductive loads on/off control
- 2.1 Valves and relays
- 2.2 Pumps and Fans ON / OFF control
- 3 Resistive loads on/off control
- 3.1 Inrush current
- 3.2 Transient junction temperature
- 3.3 Light bulb flashover
- 4 Electromagnetic compatibility standards
- 4.1 IEC 61000-4-5 standard
- 4.2 IEC 61000-4-4 standard
loads are powered by the mains in ON / OFF mode, they were initially controlled by relays. are used with others components. On the other hand, ACSs have been developed adopting a functional integration approach. control the various loads typically required in a washer appliance. Table 1. gives the RMS current of loads that can be controlled by ACS402-5SB4 or ACS108-5SA/N, in ON / OFF control mode. Table 1. ACS108 and ACS402 targeted loads
1 ACS triggering mode
1.1 Negative gate current
gate resistors are all connected to the COM terminal. No spurious triggering can then occur. inside these limits even with worst cases of dI/dt gradients at turn-on. Figure 1. Gate / MCU connection
1.2 New layout possibilities
gate operation. A second difference is that ACS have been developed in an integration goal. drive die, the common drive reference voltage must be connected to the back of the die. loop areas, and so increases the EMI immunity of the overall electronic board. Figure 2. Figure 2. Reduction of gate / MCU loop areas conduction time should be known. Figure 3. Printed circuit area reduction thanks to ACSs in SOT223 packages
2 Inductive loads on/off control
2.1 Valves and relays
2.1.1 Turn-off overvoltages are clamped by ACSs
inductance (tens of Henry). Hence, they absorb a low RMS current (typically, 10 to 50 mA). operating mode, as shown in Figure 4. Figure 4. ACS voltage and current waveforms at turn-off (230 V 35 mA RMS valve) highest, i.e. for electromagnet loads. ACSs dies thanks to their reliable planar technology.
2.1.2 Maximum switching frequency
this case, the energy absorbed by the die equals 25 mJ. Rth value, among ACS packages on offer (DIL20, TO92, SOT223, DIL8). Figure 5. Supplementary temperature eleva tion due to repetitive clampings (@
2.2 Pumps and Fans ON / OFF control
2.2.1 Application re quirements for (dI/dt)c and (dV/dt)c
2.2.2 ACS asymmetrical turn-off behavior
ACS110/ACS120 devices where the (dI/dt)c parameter is quite similar for both polarities. Figure 7. ACS402-5 and ACS108-5 (dI/dt)c typical ability versus reapplied (dV/dt)c 50 Hz line frequency (Figure 8.). Figure 8. Turn-off delay for two different pump or fan RMS current
3 Resistive loads on/off control
3.1 Inrush current
the bolt move is due to a thermal expansion of a metallic part or a wax. All these loads can be characterized by a very low resistance value in cold state. thermal door-locks. Figure 9. shows a typical inrush current in such loads. Figure 9. Inrush current in a 230 V thermal effective door-lock
3.2 Transient junction temperature
Then, according to ACS108-5 or ACS402-5 specifications, we find: Pav = 1.76 W. Equation 5, where Tjo is the initial Tj value. inrush current period, is 40° C for a TO92 package and 14° C for a DIL20 package. respect, both ACS devices are convenient for door lock operation.
3.3 Light bulb flashover
².t capability of the ACS and destroy it. Figure 10. 25 W light bulb flashover current
Electromagnetic compatibility standards AN1172
4 Electromagnetic compatibility standards
4.1 IEC 61000-4-5 standard
4.1.1 Standard requirements
The IEC 61000-4-5 standard has been established to check if systems can always work after there has been a voltage surge super-imposed to the mains. A standard voltage waveform has been chosen which embodies typical over-voltages due to thunder or disconnection of running inductive loads from the line. Two kinds of surges must be applied: 1. Line to Ground surge: in this case the maximum voltage surge is 4 kV (for aerial power network), but the energy is absorbed by the Y2 capacitors (connected between lines and ground) of the mains filter. 2. Line to Neutral surge: in this case the maximum voltage surge is 2 kV (for aerial power network, N.B: 1 kV is required for public power network) and is applied across the power device and the load controlled by this one. A Line to Neutral over-voltage is then: 1. entirely absorbed by the load if the power switch is ON; 2. entirely held by the semiconductor device if it appears while the switch is at off-state. As the Line to Neutral surge can appear at peak mains voltage, the overall amount of voltage can reach 2.4 kV. This will be higher than the break-down level of the silicon devices used in appliances. Then, in order to prevent components destruction, designers use a varistor connected across silicon devices. The overvoltage is limited below the breakdown level of the power semiconductor and the surge energy is absorbed by the metal-oxyde component.
4.1.2 ACS behavior during IEC 61000-4-5 test
When a surge appears when an ACS is OFF , the mains over-voltage is first clamped by the device. But an excessive energy surge can raise the ACS current above its breakover level. Then, the switch turns on in break over mode. Such an event is particularly stressful on the semiconductor especially so if the current and its rate of increase are both high. The worst case occurs for ACS driving low resistance, non inductive loads. For example, Figure 12. and Figure 13. have been recorded with a thermal active door lock system at low temperature. The 2 kV surge is super-imposed to the 230 V - 50 Hz mains and synchronized with its peak value, as shown on Figure 12. Figure 13. highlights the device turn-on in this mode. As the load was previously off, its resistance is cold and equals 150 Ω. In this case, the current rises at a rate of 100 A/µs and reaches 15 A. Such transient surges would damage triacs, but not ACSs which are designed to turn-on in breakover mode. No more varistor is then needed in parallel across ACSs unlike triacs. The difference between ACS and Triac + Varistor is that, with the ACS, the load is switched on during a half or one mains cycle. This can be accepted as such events happen a few times in the system's life. Reliability tests are carried out on production batches to check the ACS robustness towards IEC 61000-4-5. A standard surge generator is used directly across a load and an ACS. The load is a 150 Ω resistor, including a 3 µH parasitic inductance, to simulate a cold door-lock.
applied at the peak mains voltage, with the same bias.
4.2 IEC 61000-4-4 standard
100 pF capacitor (realized by an aluminum sheet), directly to the I/O ports of the system. similar test to check if their products can withstand fast voltage transients.
- Reduce dV/dt rates: the snubber capacitance must be high and the snubber
- Reduce the dI/dt rate at turn-on: the snubber capacitance must be low and the
snubber resistance must be high.
4.2.2 Snubber removal thanks to ACSs
wires. The trial diagram is shown in Figure 14. Figure 12. 2 kV surge on the mains Figure 13. ACS breakdown zoom
Figure 14. IEC 61000-4-4 test synopsis Figure 15. shows the OUT -COM voltage measured during a 2 kV IEC 61000-4-4 test (N.B.: gt ACS has a minimum dV/dt capability of 500 V/µs (@ Tj = 110 °C). CL value can then be reached. Figure 15. IEC 61000-4-4 test on ACS402-5 cell for a 2 kV burst
25 W light bulb
AN1172 ESD diode conduction due to kick-back Appendix B ESD diode conduction due to kick-back An over-voltage can appear across the gate and COM (or A1 for triacs) terminals at high turn-on di/dt rates. This effect is called the "kick-back". It is due to the high density current at turn-on which causes high conduction voltage drop. Since the conduction begins around the gate area, the forward voltage is in part applied to the gate. This gate spike is clamped by the micro-controller internal electrostatic discharge (ESD) diodes, which can be damaged if conduction lasts for too long. In order to prevent ESD diodes conduction, their voltage must remain negative. When considering Figure 1. at ACS turn-on, i.e. when the push transistor M1 is off and the pull transistor M2 is on, a circulating current will never occur through D2 if the current i R remains positive. This yields Equation B1. Equation B1 As M2 is conducting, its voltage drop can be neglected. Thus, the previous relation gives: Equation B2 If D1 conducts, this means that the supply voltage is held by M2, neglecting D1 drop voltage. This MOS transistor is thus in a linear mode. Its current equals its saturating level, called i sat. Now, since isat current is necessarily higher than the Vs/R ratio (in order to secure the micro- controller operation), we can write the following relationship : Equation B3 A sufficient condition to ensure that VD1 remains below zero is that Vg remains below Vs. This condition, plus Equation B2, gives the following safety rule for no ESD diode conduction: Equation B4 0VVViR gS2MR >++-=⋅ Sg VV- > Sgsatg1D VViRVV- <⋅-= SgS VVV+ <<-
To compare the kick-back effect of triacs and ACSs, a special test circuit has been defined. A2 or OUT-COM terminals. The capacitor is charged at 300 V. Figure 19. and Figure 20. despite a dI/dt which is twice as big as with the Z0109. Figure 19. Kick-back test with ACS402 Figure 20. Kick-back test with Z0109
Figure 22. Current waveform during clamping phase for 100mA / 230V RMS loads a decreasing triangular power pulse of same average value (see References, 3.). The clamping time is given by Equation C1, which gives way to the following one.
Revision history
Table 2. Document revision history 10-Jun-1999 1 Initial release. Figure 18. updated.