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AD1991ASVRL Folha de dados(PDF) 6 Page - Analog Devices |
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AD1991ASVRL Folha de dados(HTML) 6 Page - Analog Devices |
6 / 11 page REV. 0 –6– AD1991 FUNCTIONAL DESCRIPTION Device Architecture The AD1991 is an 8-transistor, audio, power output stage. The AD1991 is arranged internally as four transistor pairs that can be used as two H-bridge outputs (2-channel mode) or as four single-ended outputs (4-channel mode), using either two or four TTL compatible inputs to control the transistors. A dead time is automatically provided between the switching of the high- side transistor and low-side transistor when the control inputs change level, to ensure that both the high-side transistor and low-side transistor are never on at the same time. Clock Source and Channel Mode Selection When the AD1991 is brought out of reset, the logic levels on MODE0 and MODE1 are latched internally. MODE0 determines the internal state machine clock source. MODE1 determines the channel mode and the function of ERR0 (see Tables I and II.) When the internal clock is used, the CLK pin should not be connected. Table I. Clock Source Selection MODE0 CLK Source 0 Internal 1External Table II. Channel Mode Selection MODE1 Channel Mode ERR0 Function 0 2-Channel Mode Data Loss Detection Output 1 4-Channel Mode Low-Side Disable Input 2-Channel Mode Two loads are connected differentially—across OUTA and OUTB and across OUTC and OUTD. Inputs INB and IND are unused and should be tied to an appropriate dc voltage (see the Edge Speed and Nonoverlap Settings section). In this mode, ERR0 is an error output used to indicate data loss, which occurs when there are no transitions on INA or INC for more than 50 ms. This signal condition is hazardous in 2-channel mode because it can cause a potentially large and harmful dc voltage across the differential loads. Table III shows the input/output relationship. Table III. Input/Output Relationship in 2-Channel Mode Input Controlled Output INA OUTA, OUTB INC OUTC, OUTD 4-Channel Mode The 4-channel mode has two types of configuration: audio and power supply. Neither of these configurations require data loss detection. In the audio configuration, each single-ended load is connected to the output through a blocking capacitor, which prevents dc from reaching the load, thereby negating the need for data loss detection. While in the power supply configuration, it is desired to maintain a dc voltage on the load, also negating the need for data loss detection. When used in the power supply configuration, the four low-side transistors can also be disabled and left permanently open if desired. This allows the loads to be driven by switching only the high-side transistor on and off. ERR0 is an input in 4-channel mode and is used to select whether the four low-side transistors are enabled or disabled, with 0 selecting disabled and 1 selecting enabled. Table IV summarizes the function of ERR0 in this mode. Table V shows the input/output relationship. Table IV. ERR0 Function in 4-Channel Mode ERR0 Low-Side Transistor Status 0 Disabled 1 Enabled Table V. Input/Output Relationship in 4-Channel Mode Input Controlled Output INA OUTA INB OUTB INC OUTC IND OUTD 1-Channel Mode One load is connected differentially—across OUTA and OUTC, and OUTB and OUTD. This mono operation is established by configuring the part for 2-channel mode and externally connecting INA to INC, OUTA to OUTC, and OUTB to OUTD (see Figure 4). Thermal Protection The AD1991 features thermal protection. When the die tempera- ture exceeds approximately 135 °C, the thermal warning error output ( ERR2) is asserted. If the die temperature exceeds approximately 150 °C, the thermal shutdown error output (ERR3) is asserted. If this occurs, the part shuts down to prevent damage to the part. When the die temperature drops below approximately 120 °C, both error outputs de-assert and the part returns to nor- mal operation. Overcurrent Protection The AD1991 features overcurrent or short-circuit protection. If the current through any power transistors exceeds 5 A, the part is muted and the overcurrent error output ( ERR1) is asserted. This is a latched error and does not clear automatically. To clear the error condition and restore normal operation, the part must be reset or MUTE must be asserted and de-asserted. |
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