AD5412 external Boost function

if I want to use AD5412 external boost function, what do I need to take care?

I used NPN transistor 2N3904, but Iout was abnormal(above 20mA).

When I removed boost related schematic, AD5412 Iout is normally. Is anything I missing?

Data sheet is suggestion PBSS8110Z or MJD31C NPN transistor.

Second, everytime power up AD5412. I need to issue reset command on reset register. and then to do initial settings.

Then the Vout/Iout can work well.

if I don't S/W reset on reset register after power up, the Vout and Iout would be overange.

Data Register @ 0xFFFF --> Vout = 5.22V

1.     Data Register @ 0x0000 --> Vout = 300mV

1.    Data Register @ 0x8000 --> Vout = 2.9V


Is it cause by AVdd and DVcc power sequence? So I need to do reset for calibration registers.

I cut decription from data sheet.


If DVCC and AVDD are powered up simultaneously or the internal DVCC is enabled, the supplies should be powered up at a rate greater than, typically, 500 V/sec or 24 V/50 ms. If this cannot be achieved, issue a reset command to the AD5412/AD5422 after power-on; this performs a power-on-reset event, reading the calibration registers and ensures specified operation of the AD5412/AD5422