STP4CMPQTR datasheet(10/22 Pages) STMICROELECTRONICS

10 / 22 page

Detailed description

STP4CMP

10/22

Doc ID 15770 Rev 2

Detailed description

The STP4CMP is a charge-pump-based 4-channel LED driver designed for RGB

illumination or LCD display backlighting, using constant current topology. Each of the 4

channels can be controlled independently. When ONx is pulled high, a constant current is

sunk into the LEDx pin when a LED is connected. This constant current is defined or

programmed by the value of the resistor at ISETX pin.

5.1

Enable pin (EN)

The active high enable input pin is used to shut down the whole device. When this pin is

pulled low, the device enters into shutdown mode with only 5 µA max. current consumption.

An internal pulled down of 300 k

Ω is present at this pin.

5.2

LED turn-on pin (ONx)

When the EN pin is pulled high, the STP4CMP provides the flexibility to control the turning-

ON/OFF on the 4 channels independently through the 4 active high ON pins. To control the

brightness of each LED channel, it is possible to drive the selected ON pin with a PWM

signal with a frequency up to a minimum TON/TOFF of 33 µs. An internal pull-down of 300 kΩ

is present at these pins.

5.3

Programmable output current

The LED currents at the 4 channels are programmed individually through a resistor

connected from Iset1, Iset2, Iset3, Iset4 to ground. The relationship between the resistor (RSET)

and the LED current (ILED) is governed by this equation:

Equation 1

RSET = 16 * (1.22 / ILED)

5.4

Charge pump

The STP4CMP charge pump can be disabled or enabled according to the CP_sel pin.

When enabled (CP_sel is high), the charge pump provides a clamping voltage of typ 5.0 V

to ensure enough headroom to drive the LEDs. An internal pull-down of 300 k

Ω is present at

this pin.

The charge pump can be disabled by pulling low the CP_sel pin, based on the VCC and

forward voltage of the LEDs used. This allows the connection of VCC directly to VOUT to

drive the external LEDs.

At VCC 3.1 V, the charge pump is able to maintain regulation at 5 V when the total current

drawn from it (at VOUT pin) is ≤ 120 mA.

At 2.7

≤ VCC < 3.1 V, in order for the charge pump to maintain regulation at 5 V, the total

current drawn from it (at VOUT pin) must be lowered to ≤ 40 mA.

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