ADBMS2950BCCSZ datasheet(68/97 Pages) AD

68 / 97 page

ADBMS2950B

Data Sheet

Rev. 0 | Page 68 of 97

PROVIDING DC POWER

The primary supply pin for the ADBMS2950B is the 5V ± 0.5V

VREG input pin, which mainly supplies all references, ADCs, the

digital core, and the OC, GPIO circuitry. The VDD power input

pin supplies the DRIVE regulator, and the GPO output stages.

VDD must be connected either to VREG for 5V only operation or

to 11V to 20V supply to provide higher drive voltage on the

GPOs. There is no functional, performance or accuracy

difference between the supply options VDD = VREG = 5V and VDD

≥ 11V, VREG = 5V besides the driving capability of the GPOs

being either 5V or >11V and the DRIVE output voltage being

available only when VDD ≥ 11V. There are several ways to supply

the ADBMS2950B, as described in the following sections.

Figure 47. ADBMS2950B Power Supply Options

VDD, VREG Single 5V Supply

The VDD and VREG pins can both be supplied directly by an

external 5V supply, for example, an isolated 5VIN to 5VOUT

ADuM derivative from the Analog Devices isoPower series.

This is the easiest power supply option, with the only limitation

of the maximum GPO drive voltage being also limited to 5V.

This is suitable for most applications that do not require to

drive N-channel MOSFETS directly through the GPOs.

VDD 11V to 20V Supply

In all other supply options, a 11V to 20V supply must be

connected to the VDD power input. A 47 Ω, 100 nF RC

decoupling network is recommended for filtering and to protect

the IC from transients. shows the various options by either

using a 11V to 20V supply which is regulated down to 5V for

VREG or a 5V supply which is then boosted to 11V to 20V for

VDD. In the latter case, the internal diode from VREG to VDD is

important to note as it forbids using a boost converter or charge

pump that actively pulls-down the output when not enabled.

The lower left drawing of Figure 47 shows this diode for clarity.

11V to 20V Supply and NPN Linear Regulator

For the 11V to 20V supply, an isolated flyback or push-pull

regulator can be used. A discrete regulator with the addition of

a few external components can be formed through DRIVE pin,

as shown in Figure 46, Figure 47 upper left, and Figure 48.

The DRIVE pin provides a 5.7V output, capable of sourcing

several mA.When buffered with NPN transistor, this

configuration provides a stable 5V over temperature. Choose

the NPN transistor to have a sufficient beta value over

temperature (>40) to provide the necessary supply current. The

peak VREG current requirement of the ADBMS2950B

approaches 30 mA when simultaneously communicating over

the isoSPI and while making ADC conversions. The supply

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