Internal Reference Start Up

The internal band-gap reference has two start-up mechanisms. The first is a static mechanism that ensures some current is present in the output stage of the band gap. The second is a transient mechanism which ensures the proper output voltage. This dual start-up approach provides coverage across silicon process variations and is triggered at power-up of the DVDD supply or by toggling the power down (PD) pin.

When not in use, the ADS1605, ADS1606 and ADS1625, ADS1626 can be powered down by taking the PD pin low. All circuitry will be shutdown, including the voltage reference. There is an internal pullup resistor of 170 kΩ on the PD pin, but it is recommended that this pin be connected to a general purpose I/O pin to help ensure proper start-up of the reference when power cycling the device at cold temperatures.

When power cycling the ADS1605, ADS1606 and ADS1625, ADS1626 below –20°C, it is recommended to allow the voltage present on the VCAP pin (pin 59) to drain completely to 0 V before the application of the analog supply voltage (AVDD) and the digital supply voltage (DVDD). If the reference voltage does not recover at power-up, toggling the PD pin will allow the reference to recover. An alternate method to ensure proper reference recovery is to include a 50-kΩ resistor from VCAP (pin 59) to AVDD.