Charger 18 Click Board

How Does The Charger 18 Click Board™ Work?

The Charger 18 Click Board™ as its foundation uses the LTC3553, a micropower multifunction power management integrated circuit (PMIC) for portable Li-Ion/Polymer battery-based applications from Analog Devices. It combines a USB-compatible PowerPath manager with automatic load prioritization delivering up to 400mA battery charge current from a 5V USB input. The device's 'instant-on' operation ensures immediate system load power when a USB supply is available, even with a fully discharged battery. Alongside a stand-alone battery charger, it also has a high-efficiency synchronous 200mA buck regulator and a 150mA low dropout linear regulator available on the present onboard connectors.

The Charger 18 Click Board™ has an input current limit selection allowing the user to select between 100mA and 500mA input current limit. The choice can be made by positioning the SMD jumper labelled as ISET SEL to an appropriate position. Besides ISET, it also possesses SEQ SEL jumper selection determining which regulator is enabled before the other. The first-regulator power-up selection is made by positioning this SMD jumper to an appropriate position marked as BUCK or LDO.

On the other hand, the BON and LDO pins routed to the AN and PWM pins on the mikroBUS™ socket enable the buck and LDO regulators by setting these pins to a high logic state. Alongside these pins, the LTC3553 also includes a pushbutton input to control the two regulators and system reset - an onboard pushbutton labelled ON, also routed to the RST pin on the mikroBUS™, representing the Regulator Ignition button. Pressing the button causes an STA interrupt, informing the MCU that this event has occurred.

These regulators are also related to a Standby Mode, selectable through an SMD jumper labelled as ISET SEL. When this jumper is placed ON, the buck and the LDO regulator quiescent current are reduced to low levels while maintaining output voltage regulation. The buck regulator is limited to a 10mA maximum load current in this mode, and the LDO regulator's response to line and load transients is slower.

As already mentioned in the text, the Charger 18 Click Board™ communicates with MCU using several GPIO pins. With the IEN pin routed to the CS pin on the mikroBUS™ socket is pulled high, the LTC3553 enters Suspend mode to comply with the USB specification. In this mode, the power path between USB and VOUT is put in a high impedance state to reduce the USB input current. This Click board™ also comes with a blue LED labelled as CHARGING for battery charging state.

An NTC function is also available for temperature-qualified charging. The temperature monitoring feature is selectable via jumper labelled as NTC SEL, where the user can choose between external or internal modes of monitoring. A negative temperature coefficient (NTC) thermistor input for the battery temperature monitor is provided for external mode.

The Charger 18 Click Board™ can be operated only with a 5V logic voltage level. The board must perform appropriate logic voltage level conversion before using MCUs with different logic levels. However, the Click board™ comes equipped with a library containing functions and an example code that can be used, as a reference, for further development.

SPECIFICATIONS

PINOUT DIAGRAM

This table shows how the pinout of the Charger 18 Click Board™ corresponds to the pinout on the mikroBUS™ socket (the latter shown in the two middle columns).

Notes	Pin					Pin	Notes
Buck Enable	BON	1	AN	PWM	16	LDO	LDO Enable
Regulator Ignition	ON	2	RST	INT	15	STA	Pushbutton Status
Suspend Mode	IEN	3	CS	RX	14	NC
NC	4	SCK	TX	13	NC
NC	5	MISO	SCL	12	NC
NC	6	MOSI	SDA	11	NC
NC	7	3.3V	5V	10	5V	Power Supply
Ground	GND	8	GND	GND	9	GND	Ground

ONBOARD SETTINGS AND INDICATORS

CHARGER 18 CLICK ELECTRICAL SPECIFICATIONS