AD9980PCB datasheet(18/44 Pages) AD

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AD9980

Preliminary Technical Data

Rev. 0 | Page 18 of 44

FIELD 1

FIELD 0

SYNC SEPARATOR THRESHOLD

FIELD 1

FIELD 0

HSYNCIN

VSYNCIN

VSYNCOUT

O/E FIELD

EVEN FIELD

QUADRANT

Figure 12. Vsync Filter—Odd/Even

Power Management

To meet display requirements for low standby power, the

AD9980 includes a power-down mode. The power-down state

can be controlled manually (with Pin 17 or Register 0x1E, Bit 3),

or completely automatically by the chip. If automatic control is

selected (0x1E, Bit 4), the AD9980’s decision is based on the

status of the sync detect bits (Register 0x24, Bits 2, 3, 6,

and 7). If either an Hsync or a sync-on-green input is detected

on any input, the chip powers up, otherwise it powers down. If

manual control is desired, the AD9980 includes the flexibility of

control with both a dedicated pin and a register bit. The dedi-

cated pin allows a hardware watchdog circuit to control power-

down, while the register bit allows power-down to be controlled

by software. With manual power-down control, the polarity of

the power-down pin must be set (0x1E, Bit 2) regardless of

whether the pin is used. If unused, it is recommended to set the

polarity to active high and hardwire the pin to ground with a

10 kΩ resistor.

In power-down mode, there are several circuits that continue to

operate normally. The serial register and sync detect circuits

maintain power so that the AD9980 can be woken up from

its power-down state. The bandgap circuit maintains power

because it is needed for sync detection. The sync-on-green and

SOGOUT functions continue to operate because the SOGOUT

output is needed when sync detection is performed by a

secondary chip. All of these circuits require minimal power to

operate. Typical standby power on the AD9980 is about 50 mW.

There are two options that can be selected when in power-

down. These are controlled by Bits 0 and 1 in Register 0x1E. The

first is to determine whether the SOGOUT pin is put in high

impedance or not. In most cases, SOGOUT is not put in high

impedance during normal operation. The option to put

SOGOUT in high impedance is included mainly to allow for

factory testing modes. The second option is to keep the AD9980

powered up and only put the outputs in high impedance. This

option is useful when the data outputs from two chips are

connected on a PCB and the user wants to switch

instantaneously between the two.

Table 10.Power-Down Control and Mode Descriptions

Inputs

Mode

Auto Power-Down

Control1

Power-Down2

Sync Detect3

Powered-On or Comments

Power-Up

Everything

Power-Down

Only the serial bus, sync activity detect,

SOG, bandgap reference

Power-Up

Everything

Power-Down

Only the serial bus, sync activity detect,

SOG, bandgap reference

1 Auto power-down control is set by Register 0x1E, Bit 4.

2 Power-down is controlled by OR’ing Pin 17 with Register 0x1E, Bit 3. The polarity of Pin 17 is set by Register 0x1E, Bit 2.

3 Sync detect is determined by OR’ing Register 0x24, Bits 2, 3, 6, and 7.

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