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WM8944BECS/R 数据表(PDF) 63 Page - Cirrus Logic |
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WM8944BECS/R 数据表(HTML) 63 Page - Cirrus Logic |
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63 / 165 page  WM8944B Rev 4.3 63 has selected the LDOVDD supply voltage , then the alternate ratio “5/11” may be preferred, as described below. Note that the “5/11” ratio is designed for the case where LDOVDD = 3.3V and LDOVOUT = 3.0V. This results in a VMID = 3.3V x (5/11) = 1.5V which is half of the LDOVOUT voltage. If these conditions are not being used or the LDO has been bypassed then VMID_REF should be set to select LDOVOUT as the VMID source and VMID_CTRL should be set to select the ratio “1/2”. The speaker output drivers require a mid-rail reference voltage. The default operating conditions assume SPKVDD >= 3.0V, and use VMID as the reference. The reference can also be adjusted for SPKVDD = 1.8V. If SPKVDD = 1.8V, then the SPK_LOWVMID_ENA register should be set to 1. This selects a 0.9V mid-rail reference, enabling optimal power and THD performance at the lower SPKVDD voltage. Note that the speaker output reference is fixed with respect to LDOVOUT or LDOVDD; it does not scale with SPKVDD. Therefore, the speaker reference cannot be otimised for all SPKVDD conditions. If SPKVDD > 1.8V and < 3.0V, then SPK_LOWVMID_ENA should be set to 1, but the THD performance may be degraded. The analogue circuits in the WM8944B require a bias current. The normal (Master) bias current is enabled by setting BIAS_ENA. Note that the Master bias current source requires VMID to be enabled also. The Master Reference and Bias Control bits are defined in Table 40. REGISTER ADDRESS BIT LABEL DEFAULT DESCRIPTION R7 (07h) Additional control 10 VMID_REF_SEL 0 VMID Source Select 0 = LDO supply (LDOVDD) 1 = LDO output (LDOVOUT) 9 VMID_CTRL 0 VMID Ratio control Sets the ratio of VMID to the source selected by VMID_REF_SEL 0 = 5/11 1 = 1/2 4 VMID_ENA 0 VMID Enable 0 = Disabled 1 = Enabled R2 (02h) Power Management 1 5 SPK_LOWVMID_ ENA 0 Selects 0.9V midrail voltage for speaker output drivers 0 = Disabled 1 = Enabled This bit should be enabled if SPKVDD = 1.8V 3 BIAS_ENA 0 Master Bias Enable 0 = Disabled 1 = Enabled 1:0 VMID_SEL [1:0] 00 VMID Divider Enable and Select 00 = VMID disabled (for OFF mode) 01 = 2 x 50k divider (for normal operation) 10 = 2 x 250k divider (for low power standby) 11 = 2 x 5k divider (for fast start- up) Table 40 Reference Voltages and Master Bias Enable A pop-suppressed start-up requires VMID to be enabled smoothly, without the step change normally associated with the initial stage of the VMID capacitor charging. A pop-suppressed start-up also |
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