AFE4403 datasheet(49/97 Pages) TI

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Pulse repetition period

Sample LED2

Sample LED1

Sample Ambient 2

Sample Ambient 1

Convert LED2

Convert LED1

Convert Ambient 2

Convert Ambient 1

PDN_CYCLE

AFE4403

www.ti.com

SBAS650B – MAY 2014 – REVISED JULY 2014

8.4.1.3 Dynamic Power-Down Mode

When operated at low PRF, a dynamic power-down mode can be optionally enabled to shut off blocks during a

portion of each period. This operation is illustrated in Figure 67. The dynamic power-down signal (called

PDN_CYCLE) can be internally generated using the timing controller. PDN_CYCLE can be used to shut off

power to internal blocks during the unused section within each pulse repetition period.

Figure 67. Dynamic Power-Down Mode Timing

t1 and t2 denote the timing margin between the active portion of the period and the dynamic power-down signal.

TI recommends setting t1 > 50 µs and t2 > 200 µs in order to ensure sufficient time for the shutdown blocks to

recover from power-down. By choosing the blocks that are shut down during dynamic power-down, a power

savings of anywhere between 35% to 70% power can be achieved when the PDN_CYCLE phase is active.

The sequence of the convert phases within a pulse repetition period should be as follows: LED2 (Red)

→

Ambient 2

→ LED1 (IR) → Ambient 1. The sample phases must precede the corresponding convert phase. Also

note that the ADC_RDY signal comes at the beginning of the pulse repetition period. Thus, the contents of the

registers must be read before the completion of the first conversion phase in the pulse repetition period. These

contents correspond to the samples of the four phases from the previous pulse repetition period.

The DYNAMIC1, DYNAMIC2, DYNAMIC3, and DYNAMIC4 bits determine which blocks are powered down

during the dynamic power-down state (when PDN_CYCLE is high). For maximum power saving, all four bits can

be set to 1. TI recommends setting t1 to greater than 100 µs and t2 to greater than 200 µs to ensure that the

blocks recover from power-down in time for the next cycle.

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AFE4403 Datasheet(PDF) 49 Page - Texas Instruments