AD4134 power supply sequencing

Question

Hello, 
 1) I'm looking at powering the AD4134 using the internal LDOs. The datasheet Fig 96 shows DVDD5 connected to LDOIN - Fig 97 suggests sequencing is required so LDOIN is applied after DVDD5. Which is correct?

2) I'm reading the datasheet that IOVDD must be supplied from an external supply (can't be fed from any of the internal LDO outputs) - is this correct? 
 Kind regards, 
 Dave

JEstayo · Accepted Answer

Hi Dave, 
 
 Please refer to below for the answers to your questions. 
 
 1. You can connect the circuit as in Figure 96 where the LDOIN is connected to DVDD5 but ensure to follow the correct power sequence which is to power the 5V supply first before the 1.8V supply. 
 As it states in the datasheet "the internal LDO regulators are enabled only when the IOVDD supply is powered up first by an external 1.8V supply." 
 The supply to the 1.8 V supply pins (AVDD1V8, DVDD1V8, and CLKVDD) is provided by the 5V to LDOIN but is enabled by the 1.8V IOVDD supply, hence the LDOIN in Figure 97 is enabled when IOVDD is supplied. 
 
 2. Yes. IOVDD must be supplied from an external supply. Only the pins AVDD1V8, DVDD1V8, and CLKVDD can be supplied using the internal LDO outputs. 
 
 Regards, 
 Janine