ISL98607

4. Application Information

FN8421 Rev.1.00

Page 23 of 29

Jun.3.19

• Output load current = 100mA

• Efficiency = 80%

•L = 2.2µH

Substituting previous parameters in Equation 8 gives us:

IPk = 453mA

The ISL98607 boost regulator operates in DCM and PFM mode at light load. In PFM mode, it uses a fixed peak

inductor current of ~340mA.

To avoid the inductor core saturation, the saturation current of the inductor selected should be higher than the

greater of the peak inductor current (for CCM) and the 340mA peak current in PFM mode.

The 340mA peak inductor current in PFM mode is optimized to provide maximum efficiency with a 2.2µH inductor

value. If a smaller inductor is used, less energy is delivered per cycle, the ISL98607 switches at a higher

frequency, and the efficiency reduces. Increasing the inductor increases the energy delivered per pulse. However,

for a given inductor size the DC-resistance (DCR) increases with inductor value, so the conduction losses

increase. L = 2.2µH is the optimal value for ISL98607.

Table 3 shows the recommended inductors for typical ISL98607 applications (small size, handheld TFT-LCD

display power).

4.16.3 Output Capacitor

The output capacitor supplies current to the load during transient conditions, and reduces the ripple voltage at the

output. Output ripple voltage consists of two components:

• The voltage drop due to the inductor ripple current flowing through the ESR of the output capacitor.

• Charging and discharging of the output capacitor.

For low ESR ceramic capacitors, the output ripple is dominated by the charging and discharging of the output

capacitor. The voltage rating of the output capacitor should be greater than the maximum output voltage.

Note: Capacitors have a voltage coefficient. The effective capacitance reduces (derates) as the operating

voltage/bias increases. Always see the manufacture’s derating information to determine effective capacitance for

the operating conditions.

The effective capacitance at the nominal output voltage should be 2.2µF for VBST and VP regulator, and 4.4µF

for VN. Renesas recommends using a 10µF X5R 10V or equivalent ceramic output capacitor for both VBST and

VP outputs to provide a minimum of 2.2µF effective capacitance. For the VN output, Renesas recommends use

one or two 10µF X5R 10V or equivalent ceramic output capacitors. Using two VN output capacitors results in

<50mV peak-to-peak output voltage ripple with input voltages from 2.8V to 4.4V.

Table 3.

Recommended Inductors

Inductor Part Number

Inductance (µH)

DCR (mΩ)ISAT (A)

Footprint Size

VLF302510MT-2R2M (TDK)

2.2

70

1.23

3025

DFE252012C (Toko)

2.2

90

2.00

2520

TFM201610G-2R2M (TDK)

2.2

150

1.20

2016

Table 4.

Recommended Output Capacitors

Capacitor Part Number

Value (µF)

Size

Quantity

GRM155R61A106ME11 (Murata)

10

0402

x5: CIN, CVBST, CVP, CVN, CCP

x1: CVN (x2 for minimum ripple)

GRM188R61C475KAAJ (Murata)

4.7

0603

x5: CIN, CVBST, CVP, CVN, CCP

x1: CVN (x2 for minimum ripple)