AD7280ABSTZ datasheet(23/48 Pages) AD

23 / 48 page

AD7280A

Rev. 0 | Page 23 of 48

AUXILIARY ADC INPUTS

The AD7280A provides six single-ended analog inputs to the

ADC—AUX1 to AUX6—which can be used to convert the

voltage output of a thermistor temperature measurement circuit.

In the event that no temperature measurements are required or

that individual cell temperature measurements are not required,

the auxiliary ADC inputs can be used to convert any other 0 V

to 5 V input signal.

The AD7280A can be programmed to complete conversions on

all six auxiliary ADC channels, on three auxiliary ADC channels

(AUX1, AUX3, and AUX5), or on none of the auxiliary ADC

input channels. The number of conversions is programmed

through Bits[D15:D14] of the control register. The number of

conversion results supplied by the AD7280A for readback by

the DSP/microprocessor is programmed through Bits[D13:D12]

of the control register. It is also possible to read back a single

auxiliary ADC conversion result from each device in the daisy

chain. This can be done by programming the read register on

each device to read back the required conversion result (see

Example 4 in the Examples of Interfacing with the AD7280A

section). If the device is used in this mode, the overall conversion

sample rate should be limited by the conversion window required

for the number of channels selected by Bits[D15:D14] of the

control register.

In an application where the alert function is used but only one

or two auxiliary ADC inputs are required, the AD7280A should

first be programmed to complete and read back only three

auxiliary ADC conversions by setting Bits[D15:D12] of the

control register to 0101. Channel AUX5 and Channel AUX3 can

be removed from the alert detection by writing to Bits[D1:D0]

of the alert register (see Table 12 in the Alert Output section).

Thermistor Termination Input

If thermistor circuits are used to measure each individual cell

temperature, the thermistor termination pin, AUXTERM, can be

used to terminate the thermistor inputs for each auxiliary ADC

input measurement. This reduces the termination resistor

requirement from six resistors to one. Bit D3 in the control

Note that, due to settling time requirements, the thermistor termi-

nation resistor option should only be used when the acquisition

time of the AD7280A is set to its highest value (1.6 μs). The

acquisition time is configured by setting Bits[D6:D5] of the

control register (see Table 9).

In Figure 36, the termination resistor is placed between VSS

and AUXTERM. The AUXTERM input can be used to terminate the

thermistor inputs to the high or low voltage of the thermistor

circuit.

VSS

AUXTERM

RTERM

AUX1

AUX2

AUX3

AUX4

AUX5

AUX6

VREG

AD7280A

Figure 36. Typical Circuit Using the Thermistor Termination Resistor

POWER REQUIREMENTS

The current consumed by the AD7280A in normal operation,

that is, when not in power-down mode, is dependent on the

mode in which the part is being operated. The three distinct

modes of operation can be described as follows:

•

Voltage and auxiliary ADC input conversion

•

AD7280A configuration and data readback

•

Cell balancing

The AD7280A consumes its highest level of current while con-

verting voltage and/or auxiliary ADC inputs to digital outputs.

Depending on the configuration of the AD7280A, the conversion

time can be as little as 6 μs. The typical current required by the

AD7280A during conversion is 6.9 mA (see Table 2).

When configuring a chain of AD7280As or when reading back

the voltage and/or auxiliary ADC conversion results from a chain

of AD7280As, the current required for each AD7280A is typically

6.5 mA (see Table 2). The time required to read back the voltage

conversions results from 48 lithium ion cells depends on the

speed of the interface clock used, that is, SCLK, but it can be as

low as 1.54 ms.

The typical current consumed by the AD7280A when the cell

balance outputs are switched on is 6.4 mA (see Table 2). The

length of time for which the cell balance outputs are switched

on is defined by the user.

When the AD7280A is not being used in any of the aforemen-

tioned modes of operation, it is recommended that the device

be powered down, as described in the Power-Down section.

This significantly reduces the current drawn by each AD7280A

in the chain, which avoids unnecessary draining of the lithium

ion cells and aids in current matching between devices across

the full battery stack.

AD7280ABSTZ Datasheet(PDF) 23 Page - Analog Devices

AD7280ABSTZ Datasheet(HTML) 23 Page - Analog Devices

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

Datasheet Descarga

Enlace URL