CDH2D09 datasheet(34/44 Pages) MAXIM

34 / 44 page

PMIC with Integrated Charger and

Smart Power Selector for Handheld Devices

______________________________________________________________________________________

Step-Down Inductor

Choose the step-down regulator inductance to be

4.7µH. The minimum recommended saturation current

requirement is 600mA. In PWM mode, the peak induc-

tor currents are equal to the load current plus one half

of the inductor ripple current. The MAX8671X works

well with physically small inductors. See Table 6 for

suggested inductors.

The peak-to-peak inductor ripple current during PWM

operation is calculated as follows:

where fS is the 2MHz switching frequency.

The peak inductor current during PWM operation is cal-

culated as follows:

Step-Down Converter Output Current

The three MAX8671X step-down regulators each pro-

vide at least 425mA of output current when using a rec-

ommended inductor (Table 6). To calculate the

maximum output current for a particular application and

inductor use the following two-step process (as shown

in Figure 10):

1) Use the following equation to calculate the approxi-

mate duty cycle (D):

where:

VOUT = output voltage

IOUTTAR = target (desired) output current—cannot

be more than the minimum p-channel current-limit

threshold

RN = n-channel on-resistance

RP = p-channel on-resistance

RL = external inductor’s ESR

VIN = input voltage—MAXIMUM

2) Use the following equation to calculate the maximum

output current (IOUTMAX):

where:

ILIM = p-channel current-limit threshold—MINIMUM

VOUT = output voltage

D = approximate duty cycle derived from step 1

f = oscillator frequency—MINIMUM

L = external inductor’s inductance—MINIMUM

RN = n-channel on-resistance

RL = external inductor’s ESR

OUTMAX

LIM

OUT

−

××

−

××

()

OUT

OUTTAR

+−

()

L PEAK

LOAD

=+ −

OUT

SYS

OUT

SYS

− =

−

××

()

MANUFACTURER

SERIES

INDUCTANCE

(µH)

ESR (

Ω)

CURRENT RATING

(mA)

DIMENSIONS (mm)

CDRH2D11HP

4.7

190

750

3.0 x 3.0 x 1.2 = 10.8mm

Sumida

CDH2D09

4.7

218

700

3.0 x 3.0 x 1.0 = 9.0mm

NR3012

4.7

130

770

3.0 x 3.0 x 1.2 = 10.8mm

Taiyo Yuden

NR3010

4.7

190

750

3.0 x 3.0 x 1.0 = 9.0mm

VLF3012

4.7

160

740

2.8 x 2.6 x 1.2 = 8.7mm

TDK

VLF3010

4.7

240

700

2.8 x 2.6 x 1.0 = 7.3mm

DE2812C

4.7

130

880

3.0 x 2.8 x 1.2 = 10.8mm

TOKO

DE2810C

4.7

180

640

3.0 x 2.8 x 1.0 = 8.4mm

Table 6. Suggested Inductors

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