LTC4012 datasheet(9/18 Pages) AD

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LTC2959

Rev. 0

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OPERATION

the instantaneous current through the sense resistor, the

temperature of the chip, as well as the voltage on the

GPIO pin.

ADC conversions can be triggered in a one-shot, periodi-

cal or continuous manner, as set by programming the ADC

control register via the I2C interface. Each ADC conversion

takes about 400µs to complete.

Initiating a single-shot conversion sequence will cause

the ADC to execute the following sequence:

1) 400μs ADC startup

2) 400μs voltage conversion

3) 400μs current conversion

4) 400μs temperature conversion

5) 400µs GPIO conversion (optional)

6) ADC power down

Afterwards, all data is available in the corresponding reg-

isters. To include the GPIO channel into the ADC measure-

ments, set register B[4:3] appropriately and configure its

full-scale range using B[3].

By default, the ADC operates in sleep mode, in which no

conversions are performed. The ADC can also be operated

in smart sleep mode, in which the ADC converts voltage,

current, temperature (and GPIO) once every 52 seconds.

The threshold and min/max registers are also updated,

and alerts will trigger appropriately when the LTC2959 is

configured as such.

The ADC can also be configured to continuously convert

voltage or current, or voltage and current alternatively. In

a continuous mode, the ADC startup time sequence step

only takes place at the very beginning of ADC operation.

Measuring a single quantity continuously leads to a sam-

pling rate of 2.5kS/s.

Voltage ADC Input Range

The accuracy of the ADC Voltage channel is only guaran-

teed for input voltages between 1.8V and 60V.

Power-Up Sequence

When VDD rises above a threshold of approximately

1.45V, the LTC2959 generates an internal power-on reset

(POR) signal that sets all registers to their default state. In

the default state, the coulomb counter is active while the

multi-purpose ADC operates in sleep mode. The accumu-

lated charge register is set to mid-scale (80000000h) and

all ADC channel outputs are set to 0000h. All threshold

registers and the min-max tracking registers are set to

their default values. The min/max tracking registers of the

ADC will update upon completion of the first ADC con-

version. The GPIO pin is configured as an analog input;

the ALERT and Charge Complete functionalities are not

enabled at startup.

Preventing Violation of Absolute Maximum Ratings

The small size, robustness and low impedance of ceramic

capacitors make them an attractive option for the supply

bypass capacitor of LTC2959. However, these capacitors

can cause problems if the LTC2959 is plugged into a live

supply close to its maximum voltage of 65V. The low-

loss ceramic capacitor, combined with stray inductance

in series with the power source, forms an underdamped

tank circuit, and the voltage at the VDD pin or the SENSE

pins of the LTC2959 can ring several tens of volts, pos-

sibly exceeding the LTC2959 rating and damaging the

part. This can be prevented by adding a transient voltage

suppression diode to the appropriate pin.

Additionally, when operating at high VDD or SENSE volt-

ages (>20V), care should be taken not to pull the digital

communication pins SCL, SDA and GPIO below their

absolute minimum operating voltage of –0.3V. This

may occur, for example, due to differences between the

local GND and the GND of the connected microcontrol-

ler. This will increase the supply current, and the asso-

ciated increase in power dissipation might damage the

part. This can be prevented by adding Schottky diodes to

these communication lines, connecting the anodes to the

LTC2959 GND pin.

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