WM8945ECSSLASHR datasheet(82/169 Pages) WOLFSON

82 / 169 page

WM8945

Production Data

PD, May 2011, Rev 4.1

The resistance RREF is a function of the circuit gain and a function of the parallel combination of

RSOURCE and RLOAD. When VB_GAIN = 0 (0dB gain), the current gain of the video buffer is 5, as

described by the equation IVBOUT = 5 x IVBREF.

The resistor RREF should be set equal to 5 x (RSOURCE // RLOAD), where (RSOURCE // RLOAD) is the effective

resistance of the parallel combination of RSOURCE and RLOAD. (Note that the required resistance RREF is

the same for both settings of VB_GAIN.)

In a typical application, RLOAD = 75, RSOURCE = 75, RREF = 187.

RECOMMENDED VIDEO BUFFER INITIALISATION SEQUENCE

Power Up (Video signal AC coupled to Video Buffer input):

ACTION

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_REF_SEL_FAST = 1

LDO_BIAS_SRC = 1

LDO_ENA = 1

R53 (35h) [14]

R53 (35h) [5]

R53 (35h) [15]

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 150ms to allow VMID to settle

VMID_ENA = 1

R7 (07h) [4]

Set LDO for normal operation

LDO_REF_SEL_FAST = 0

LDO_BIAS_SRC = 0

R53 (35h) [14]

R53 (35h) [5]

Set VMID for normal operation

VMID_FAST_START = 0

STARTUP_BIAS_ENA = 0

R7 (07h) [11]

R7 (07h) [8]

Set VMID divider for normal operation

VMID_SEL = 01

R2 (02h) [1:0]

Enable VMID

Delay 150ms to allow VMID to settle

VMID_ENA = 1

R7 (07h) [4]

Set LDO for normal operation

LDO_REF_SEL_FAST = 0

LDO_BIAS_SRC = 0

R53 (35h) [14]

R53 (35h) [5]

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

VB_ENA = 1

R38 (26h) [7]

Delay 20ms for buffer to capture input

level

Disable Video Buffer Pulldown

VB_PD = 0

R38 (26h) [1]

WM8945ECS/R датащи(PDF) 82 Page - Wolfson Microelectronics plc

WM8945ECS/R датащи(HTML) 82 Page - Wolfson Microelectronics plc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

датащи скачать

ссылки URL