WM8944BECSSLASHR datasheet(85/165 Pages) CIRRUS

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WM8944B

Rev 4.3

RECOMMENDED VIDEO BUFFER INITIALISATION SEQUENCES

Recommended power-up sequences for Video Buffer applications are described in Table 58 and

Table 59.

DESCRIPTION

LABEL

Turn on external supplies and wait for the supply voltages to settle.

Reset registers to default state (software reset).

SW_RESET

R0 (00h) [15:0]

Enable VMID Fast Start and Start up Bias.

Select Start-Up Bias and set VMID soft start for start-up ramp.

VMID_FAST_START = 1

STARTUP_BIAS_ENA = 1

BIAS_SRC = 1

VMID_RAMP[1:0] = 01

R7 (07h) [11]

R7 (07h) [8]

R7 (07h) [7]

R7 (07h) [6:5]

If using VMID as the reference voltage for the LDO then select VMID

fast start or set to 0 if using the Bandgap as the reference voltage for

LDO. Select LDO Start-Up Bias and enable LDO.

Delay 300ms for LDO to settle.

LDO_ENA = 1

LDO_REF_SEL_FAST = 1

LDO_BIAS_SRC = 1

R53 (35h) [15]

R53 (35h) [14]

R53 (35h) [5]

Enable VMID Buffer and Master Bias.

Set VMID_SEL[1:0] for fast start-up.

BIAS_ENA = 1

VMID_BUF_ENA = 1

VMID_SEL[1:0] = 11

R2 (02h) [3]

R2 (02h) [2]

R2 (02h) [1:0]

Enable VMID.

Delay 50ms to allow VMID to settle.

VMID_ENA = 1

R7 (07h) [4]

Set LDO and VMID for normal operation.

LDO_REF_SEL_FAST = 0

LDO_BIAS_SRC = 0

VMID_FAST_START = 0

STARTUP_BIAS_ENA = 0

VMID_SEL = 01

R53 (35h) [14]

R53 (35h) [5]

R7 (07h) [11]

R7 (07h) [8]

R2 (02h) [1:0]

Set Video Buffer Gain as required.

VB_GAIN

R38 (26h) [5]

Set Video Buffer Filter Q Boost as required.

VB_QBOOST

R38 (26h) [6]

Enable Video Buffer Clamp.

VB_CLAMP = 1

R38 (26h) [0]

Enable Video Buffer Pulldown.

VB_PD = 1

R38 (26h) [1]

Enable video buffer.

Delay 20ms for buffer to capture input level.

VB_ENA = 1

R38 (26h) [7]

Disable Video Buffer Pulldown.

VB_PD = 0

R38 (26h) [1]

Table 58 Power-Up Sequence (Video Signal AC-coupled to Video Buffer input)

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