MIC2870 datasheet(13/25 Pages) MICREL

13 / 25 page

Micrel, Inc.

MIC2870

September 5, 2013

Revision 1.0

Functional Description

VIN

The

input

supply

provides

power

the

internal

MOSFETs gate drive and controls circuitry for the switch-

mode regulator. The operating input voltage range is from

2.7V to 5.0V. A 4.7µF low-ESR ceramic input capacitor

should be connected from VIN to AGND as close to

MIC2870 as possible to ensure a clean supply voltage for

the device. The minimum voltage rating of 10V is

recommended for the input capacitor.

The MIC2870 has internal low-side and synchronous

MOSFET switches. The switch node (SW) between the

internal MOSFET switches connects directly to one end

of the inductor and provides the current paths during

switching cycles. The other end of the inductor is

connected to the input supply voltage. Due to the high-

speed switching on this pin, the switch node should be

routed away from sensitive nodes wherever possible.

AGND

This is the ground path for the internal biasing and control

circuitry. The current loop of the analog ground should be

separated from that of the power ground (PGND). AGND

should be connected to PGND at a single point.

PGND

The power ground pin is the ground path for the high

current in the boost switch and the ground path of the

LED current sinks. The current loop for the power ground

should be as small as possible and separate from the

AGND loop as applicable.

OUT

Boost converter output pin which is connected to the

anode of the LED. A low-ESR ceramic capacitor of 2.2µF

or larger should be connected from OUT to PGND as

close as possible to the MIC2870. The minimum voltage

rating of 10V is recommended for the output capacitor.

LED1/LED2

The current sink pins for the LED(s). The LED anode is

connected to the OUT pin and the LED cathode is

connected to the LED1/LED2 pin(s).

This is the enable pin of the MIC2870. The MIC2870 is in

standby mode when the EN pin is asserted high. If this

pin is driven low for more than 1s, the IC is shutdown.

Alternatively,

the

2C interface can be used for

enabling/disabling

the

through

the

master

control/status register. EN is pulled down by an internal

resistor.

FEN

FEN is the hardware enable pin for flash mode. A logic

low-to-high transition on FEN pin initiates the flash mode.

If FEN pin is left floating, it is pulled down internally by a

built-in 1µA current source when the device is enabled.

Flash mode is terminated when FEN is pulled low or left

floating, and the flash control register is cleared.

TEN

TEN is the hardware enable pin for torch mode. A logic

low-to-high transition on TEN pin initiates the torch mode.

If TEN pin is left floating, it is pulled down internally by a

built-in 1µA current source when the device is enabled.

Torch mode is terminated when TEN is pulled low or left

floating, and the torch control register is cleared.

FI is the flash inhibit pin. When this pin is high in flash

mode, both LED1 and LED2 currents are changed from

the flash-mode current level to the torch-mode current

level. When this pin is low, both LED1 and LED2 currents

are changed from torch-mode current level back to the

original flash-mode current level.

FRSET

The

flash-mode

maximum

LED

current

level

programmed through FRSET. A resistor connected from

FRSET to AGND sets the maximum current in the flash

mode. FRSET can be grounded for the default flash-

mode current of 0.75A. For best current accuracy, a 0.1%

tolerance resistor is recommended. FRSET cannot be left

floating and the maximum resistance is limited to 80kΩ.

TRSET

The

torch-mode

maximum

LED

current

level

programmed through TRSET. A resistor connected from

the TRSET pin to AGND sets the maximum current in the

torch mode. TRSET can be grounded for the default

torch-mode

current

187.5mA.

For

best

current

accuracy, a 0.1% tolerance resistor is recommended.

TRSET cannot be left floating and the maximum

resistance is limited to 80kΩ.

SCL

2C clock input pin provides a reference clock for clocking

in the data signal. This is a high-speed mode up to

3.4MHz input pin, and requires a 4.7kΩ pull-up resistor.

SDA

2C data input/output pin allows for data to be written to

and read from the MIC2870. This is a high-speed mode

up to 3.4MHz I

2C pin,

and requires a 4.7kΩ pull-up

resistor.

MIC2870 Datasheet(PDF) 13 Page - Micrel Semiconductor

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