ADP5090

Data Sheet

Rev. C | Page 12 of 21

THEORY OF OPERATION

The ADP5090 combines a nano powered boost regulator with a

storage elements management controller. It converts power

from low voltage, high impedance dc sources such as PV cells,

TEGs, and piezoelectric modules. The device stores power in

the rechargeable battery or capacitor with storage protection, and

provides power to the load. It can also control an additional

power path from a primary battery cell to the system.

The ADP5090 includes a cold start up circuit, a synchronous

boost controller with integrated MOSFETs, a charge controller

with an integrated switch, and switches for the backup power

path. The boost can be stopped temporarily by an external

signal to prevent interference with RF transmission.

The cold startup circuit is required when the VIN pin is above

controller start working. The charge-pump cold startup circuit

extracts the energy available at the VIN pin and charges the

energy harvester must supply sufficient power to complete cold

startup (see the Energy Harvester Selection section for more

information). The cold start circuit, with lower efficiency compared

to the boost regulator, can achieve a short startup time, creating

a low shutdown current system load enabled by the PGOOD

signal. To bypass the cold startup, place a primary battery at the

BACK_UP pin (see the Backup Storage Path section for more

information).

The switching mode synchronous boost regulator, with an

external inductor connected between the VIN and SW pins,

operates in pulse frequency mode (PFM), transferring energy

stored in the input capacitor to the system load (SYS) and

energy storage connected to the BAT pin. The boost control

loop regulates the VIN voltage at the level sampled at the MPPT

pin and stored at the capacitor connected to the CBP pin. To

maintain the high efficiency of the regulator across a wide input

power range, the current sense circuitry employs the internal

dither peak current limit to control the inductor current.

The boost regulator operation turns off the SYS and BAT switches

as an asynchronous mode via the energy storage controller when

the BAT pin voltage is below the battery discharging protection

threshold programmed at the SETSD pin, or stops switching when

the BAT pin voltage is above the battery overcharging threshold

programmed at the TERM pin. The boost regulator is disabled

when the voltage of the CBP pin decreases to the threshold set

by the resistor at the MINOP pin. In addition, the boost is

periodically stopped by the open voltage sampling circuit, and

can be temporary disabled by driving the DIS_SW pin high.

VIN OPEN CIRCUIT AND MPPT

The boost regulation reference is the VIN pin open circuit

voltage scaled to a ratio programmed by the resistor divider at

the MPPT pin. This voltage is periodically sampled and stored

in the capacitor connected to the CBP pin. This storage keeps

the VIN voltage operating at the level of maximum power points

available from the energy harvester at the input of the ADP5090.

The reference voltage refreshes every 19 sec by periodically

disabling the boost regulator for 296 ms and sampling the open

circuit voltage. The reference voltage is set by the following

equation:

(

)













+

=

OC2

OC1

OC1

IN

MPPT

R

R

R

Circuit

Open

V

V

(1)

The typical MPPT ratio depends on the type of harvester. For

example, it is around 0.8 for PV cells, and 0.5 for TEGs. The

MPPT can be disabled and left floating. Set the CBP pin to an

external voltage reference lower than the VIN voltage. If the input

source is an ideal voltage source, connect the MPPT and CBP pins

to ground.

ENERGY STORAGE CHARGE MANAGEMENT

Energy storage is connected to the BAT pin. The storage can be

a rechargeable battery, super capacitor, or 100 μF or larger

capacitor. The energy storage controller manages the charging

and discharging operations, monitors the SYS pin voltage, and

asserts the PGOOD signal high when it is above the threshold

programmed at the SETPG pin.

When the BAT pin voltage exceeds the charging protection

threshold programmed at the TERM pin, the boost operation

terminates to prevent battery overcharging. The overcharging

protection threshold is programmable from 2.2 V to 5.2 V.

When the BAT voltage drops below the discharging protection

threshold level programmed at SETSD pin, the switches between

the BAT pin and SYS pin are opened to prevent a deep, destructive

battery discharge, and the boost reaches asynchronous mode.

Although there is no current limit at the SYS and BAT pins, it is

recommended to limit the system load current to lower than

800 mA. The large system load current generates a droop between

the SYS pin and the rechargeable battery at the BAT pin, with

consideration given to the resistance of the SYS switch, the BAT

switch, and the rechargeable battery internal resistance.

When no input source is attached, discharge the SYS pin to ground

before attaching a storage element to the BAT pin. After hot

plugging a charged storage element, release the SYS pin because

off to protect the storage element until the SYS voltage reaches

lowest leakage (0.5 nA, typical) that allows a long store period

without discharging the storage element on BAT.