20
X-EM21V
1
2
3
4
A
B
C
D
E
F
1
2
3
4
5.3 PROTECTION CIRCUIT
TDA7491HV
[AMP IC periphery circuit]
[Protection operation]
Over-volta
g
e protection (OVP)
If the supply voltage (IC302 pins 6,7,12,13) exceeds 20
V
(nominal) the over-voltage protection is activated which forces the
outputs (SP-OUT 2,3,
8
,9,10,11,16,17) to the high-impedance state.
When the supply voltage drops to below the threshold value the device works again.
Under-volta
g
e protection (UVP)
If the supply voltage (IC302 pins 6,7,12,13) drops below 4
V
(nominal) the under-voltage protection is activated which forces
the outputs (SP-OUT 2,3,
8
,9,10,11,16,17) to the high-impedance state.
When the supply voltage recovers the device works again.
Over-current protection (OCP)
If the output current (IC302 pins 2,3,
8
,9,10,11,16,17) exceeds 4 A (nominal) the over-current protection is activated which
forces the outputs (SP-OUT 2,3,
8
,9,10,11,16,17) to the high-impedance state. Periodically, the device attempts to works again.
If the over-current condition is still present then the OCP remains active.
The period time for operation return (TOC), is determined by the R-C components (R313, C309 on upper figure) connected to
pin STBY. Of this time, the period time: 33 kohm × 2.2 uF = 72.6 ms
Thermal protection (OTP)
If the junction temperature, Tj, reaches 145° C (nominally), the device goes to mute mode and the positive and negative PWM
outputs (IC302 pins 2,3,
8
,9,10,11,16,17) are forced to 50% duty cycle. At Tj = 155° C (nominally), the device shuts down and
the output (SP-OUT 2,3,
8
,9,10,11,16,17) is forced to the high impedance state. When the device cools sufficiently the device
works again.
[DIAG Pin (Pin 28) Explanation]
Behavior of pin DIAG for various protection conditions
Dia
g
nostic output
The output pin DIAG is an open drain transistor. When the protection is activated it is in the high-impedance state (Logic H).
The pin can be connected to a power supply (< 20
V
) by a pull-up resistor whose value is limited by the maximum sinking
current (200 µA) of the pin.
Pin 2
8
(DIAG): Error diagnosis output terminal
[STBY pin (Pin 20) periphery circuit]
