AFE5801 datasheet(26/46 Pages) TI

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AFE5801

SLOS591D – SEPTEMBER 2008 – REVISED MAY 2010

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VCA_LOW_NOISE_MODE

Address: 7[10]

Setting this bit to 1 reduces the equivalent input noise of the VCA to 5nv/

√Hz (for a 51dB gain) at the

expense of an increased power consumption (5mW increase per channel).

TGC CONTROL REGISTER MAP

The TGC operation is described in the VGA/TGC Operation section that follows. This section describes the TGC

control registers which can be accessed by writing 1 to TGC_REG_WREN bit. The following table describes the

ADDRESS

D[15:7]

D[8]

D[7]

D[6]

D[5]

D[4]

D[3]

D[2]

D[1]

D[0]

0x01...0x94

REG_VALUES

0x95

START_INDEX

0x96

STOP_INDEX

INTERP_

0x97

START_GAIN

ENABLE

0x98

HOLD_ GAIN _TIME

NOT USED

UNIFORM_

SOFT_

STATIC_

0x99

GAIN_

FINE_GAIN

SYNC

PGA

MODE

0x9A

COARSE_GAIN

0x9B

UNIFORM_GAIN_SLOPE

REG_VALUE

Address: 0x01[8:0] to 0x94[8:0]

Each of these 9 bit registers (148 of them) stores the time to stay at a given gain setting, during the gain

ramp. The most significant bit of each register (REG_VALUE<8>) denotes either increment or decrement

gain from current gain value. The other 8 bits (REG_VALUE<7:0>) denote the time (a multiple of 8 × Tclk;

Tclk being the channel sampling clock, i.e., double the period of the device input clock) for the change of the

gain from the CURRENT_GAIN to CURRENT_GAIN ±1dB (depending on the REG_VALUE<8>). The fastest

ramp (shortest time) for this 1dB gain change is set by REG_VALUE<7:0> equal to 0x00 and it is 8 × Tclk.

The slowest ramp (longest time) for this 1dB gain change is set by REG_VALUE<7:0> equal to 0xFF, and it

is 255 × 8 × Tclk (see VGA operation – described later).

START_INDEX

Address: 0x95[7:0]

This 8 bit register specifies/points to the first REG_VALUE register of the TGC curve (i.e., where the curve

starts) and can have values ranging from 1 to 148 (in decimal).

STOP_INDEX

Address: 0x96[7:0]

This 8 bit register specifies/points to the last REG_VALUE register of the TGC curve (i.e., where the curve

finishes) and can have values ranging from 1 to 148 (in decimal).

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