ADN8834ACPZ-R2 datasheet(21/27 Pages) AD

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Data Sheet

ADN8834

Rev. B | Page 21 of 27

This voltage drop is proportional to the value of the DCR and it

reduces the output voltage range at the TEC.

When selecting an inductor, ensure that the saturation current

rating is higher than the maximum current peak to prevent sat-

uration. In general, ceramic multilayer inductors are suitable for low

current applications due to small size and low DCR. When the

noise level is critical, use a shielded ferrite inductor to reduce the

electromagnetic interference (EMI).

Table 7. Recommended Inductors

Vendor

Value

Device No.

Footprint

Toko

1.0 µH ± 20%,

2.6 A (typical)

DFE201612R-H-1R0M

2.0 × 1.6

Taiyo

Yuden

1.0 µH ± 20%,

2.2 A (typical)

MAKK2016T1R0M

2.0 × 1.6

Murata

1.0 µH ± 20%,

2.3 A (typical)

LQM2MPN1R0MGH

2.0 × 1.6

Capacitor Selection

The output capacitor selection determines the output voltage

ripple, transient response, as well as the loop dynamic response

of the PWM amplifier output. Use the following equation to

select the capacitor:

(

)

OUT

∆

)

(

–

Note that the voltage caused by the product of current ripple,

ΔIL, and the capacitor equivalent series resistance (ESR) also

add up to the total output voltage ripple. Selecting a capacitor

with low ESR can increase overall regulation and efficiency

performance.

Table 8. Recommended Capacitors

Vendor

Value

Device No.

Footprint

(mm)

Murata

10 µF ±

10%, 10 V

ZRB18AD71A106KE01L

1.6 × 0.8

Murata

10 µF ±

20%, 10 V

GRM188D71A106MA73

1.6 × 0.8

Taiyo

Yuden

10 µF ±

20%, 10 V

LMK107BC6106MA-T

1.6 × 0.8

INPUT CAPACITOR SELECTION

On the PVIN pin, the amplifiers require an input capacitor

to decouple the noise and to provide the transient current to

maintain a stable input and output voltage. A 10 µF ceramic

capacitor rated at 10 V is the minimum recommended value.

Increasing the capacitance reduces the switching ripple that

couples into the power supply but increases the capacitor size.

Because the current at the input terminal of the PWM amplifier

is discontinuous, a capacitor with low effective series inductance

(ESL) is preferred to reduce voltage spikes.

In most applications, a decoupling capacitor is used in parallel

with the input capacitor. The decoupling capacitor is usually a

100 nF ceramic capacitor with very low ESR and ESL, which

provides better noise rejection at high frequency bands.

POWER DISSIPATION

This section provides guidelines to calculate the power

dissipation of the ADN8834. Approximate the total power

dissipation in the device by

PLOSS = PPWM + PLINEAR

where:

PLOSS is the total power dissipation in the ADN8834.

PLINEAR is the power dissipation in the linear regulator.

PWM Regulator Power Dissipation

The PWM power stage is configured as a buck regulator and

its dominant power dissipation (PPWM) includes power switch

conduction losses (PCOND), switching losses (PSW), and transition

losses (PTRAN). Other sources of power dissipation are usually

less significant at the high output currents of the application

thermal limit and can be neglected in approximation.

Use the following equation to estimate the power dissipation of

the buck regulator:

PLOSS = PCOND + PSW + PTRAN

Conduction Loss (PCOND)

The conduction loss consists of two parts: inductor conduction

loss (PCOND_L) and power switch conduction loss (PCOND_S).

PCOND = PCOND_L + PCOND_S

Inductor conduction loss is proportional to the DCR of the output

inductor, L. Using an inductor with low DCR enhances the overall

efficiency performance. Estimate inductor conduction loss by

PCOND_L = DCR × IOUT2

Power switch conduction losses are caused by the flow of the

output current through both the high-side and low-side power

switches, each of which has its own internal on resistance (RDSON).

Use the following equation to estimate the amount of power

switch conduction loss:

PCOND_S = (RDSON_HS × D + RDSON_LS × (1 − D)) × IOUT2

where:

RDSON_HS is the on resistance of the high-side MOSFET.

D is the duty cycle (D = VOUT/VIN).

RDSON_LS is the on resistance of the low-side MOSFET.

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