ADP5091ACPZ-1-R7 datasheet(23/28 Pages) AD

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Data Sheet

ADP5091/ADP5092

Rev. A | Page 23 of 28

APPLICATIONS INFORMATION

The ADP5091/ADP5092 extract the energy from the VIN pin

to charge the SYS and the BAT pins. This process occurs in

three stages: cold start, asynchronous boost, and synchronous

boost. This section describes the procedures for selecting the

external components to maintain the energy transmission

system with the layout and assembly considerations.

ENERGY HARVESTER SELECTION

The energy harvester input source must provide a minimum level

of power for cold start, asynchronous boost, and synchronous

boost. To estimate the minimum input power required to

complete the cold start using the following equation:

VIN × IIN × ηCOLD > VSYS_TH × ISYS_LOAD

(13)

where:

VIN is clamped to VIN_COLD = 380 mV (typical), which indicates

the minimum input voltage for cold start.

IIN is the input current.

ηCOLD is the cold start efficiency, which is about 5% to 7%.

(VSYS_TH is the end of cold start operation.

ISYS_LOAD is the system load current of the SYS pin. Minimizing

the system load accelerates the cold start. Programming the

PGOOD threshold to enable the system load current is

recommended.

After the ADP5091/ADP5092 complete the cold start, the MPPT

function enables. To meet the average system load current, the

input source must provide the boost regulator with enough power

to fully charge the storage element while the system is in low

power or sleep mode. To estimate the power required by the

system, use the following equation:

VIN × IIN × ηBOOST > VBAT_TERM × (ISTR_LEAK + ISYS_LOAD)

(14)

where:

VIN is regulated to the MPPT pin voltage (MPPT ratio × OCV).

IIN is the input current.

ηBOOST is the boost regulator efficiency. See Figure 5 through

Figure 12 in the Typical Performance Characteristics section for

more information.

VBAT_TERM is the battery terminal charging threshold (see Table 1).

ISTR_LEAK is the storage element leakage current at the BAT pin.

ISYS_LOAD is the average system load current of the SYS pin.

Table 10. Recommended Solar Cells

Vendor

Device Type

Alta Devices

GaAs

Fujikura

Dye sensitized solar cell

Gcell

Dye sensitized solar cell

ElectricFilm

Dye sensitized solar cell

ENERGY STORAGE ELEMENT SELECTION

To protect the storage element from overcharging or overdis-

charging, the storage element must be connected to the BAT pin

and the system load tied to the SYS pin. The ADP5091/ADP5092

support many types of storage elements, such as rechargeable

batteries, super capacitors, and conventional capacitors. A

storage element with a 100 µF equivalent capacitance is required

to filter the pulse currents of the PFM switching converter. The

storage element capacity must provide the entire system load

when the input source is no longer generating power.

If there is a high pulse current or the storage element has

significant impedance, it may be necessary to increase the SYS

capacitor from the 4.7 µF minimum, or add additional capacitance

to the BAT pin to prevent a droop in the SYS voltage. Note that

increasing the SYS capacitor causes the boost regulator to operate

in the less efficient cold start stage for a longer period at startup.

If the application is unable to accept the longer cold start time,

place the additional capacitor parallel to the storage element. See

the Capacitor Selection section for more information.

INDUCTOR SELECTION

The boost regulator needs an appropriate inductor for proper

operation. The inductor saturation current must be at least 30%

higher than the expected peak inductor currents, as well as a

low series resistance (DCR) to maintain high efficiency. The

boost regulator internal control circuitry is designed to optimize

the efficiency and control the switching behavior with a nominal

inductance of 22 µH ± 20%. Table 11 lists some of the

recommended inductors.

Table 11. Recommended Inductors

Vendor

Device No.

L (µH)

ISAT (A)1

IRMS (A)2

DCR (mΩ)

Würth Elektronik

74437324220

470

744042220

0.6

0.88

255

Coilcraft

LPS4018-223M

0.8

0.65

360

ISAT is the dc current that causes the 20% inductance drop from its value without current.

IRMS is the current that causes a 20°C rise from a 25°C ambient temperature.

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