ADM8845(RevD) Ver la hoja de datos (PDF) - Analog Devices

Número de pieza

componentes Descripción

Fabricante

ADM8845
(Rev.:RevD)

Charge Pump Driver for LCD White LED Backlights

Analog Devices 

Data Sheet

POWER EFFICIENCY

The ADM8845 power efficiency (η) equations are the following:

η = POUT/PIN

PIN = ((VCC × ILOAD × Gain) + (IQ × VCC))

POUT = 6 × (VF × ILED)

where:

Gain is equal to the charge pump mode (1×, 1.5×, 2×).

IQ is the quiescent current of the ADM8845, 2.6 mA.

VF is the LED forward voltage.

3.4V IIN

VCC

VOUT

ILOAD

ADM8845

VCC

RSET

CTRL1

CTRL2

FB1

FB2

FB3

FB4

ISET GND

FB5

FB6

Figure 34. Charge Pump Power Efficiency Diagram

Example 1 and Example 2 show calculations of the ADM8845

power efficiency. See Figure 34 as well.

ADM8845

Example 1

The ADM8845 driving six white LEDs with a 20 mA/LED at

VCC = 3.4 V (1.5× mode) and LED VF = 4.5 V.

PIN = ((VCC × ILOAD × Gain) + (VCC × IQ))

PIN = ((3.4 × 120 mA × 1.5) + (3.4 × 2.6 mA))

PIN = ((0.612) + (0.00884))

PIN = 0.62084

POUT = 6 × (VF × ILED)

POUT = 6 × (4.5 V × 20 mA)

POUT = 0.54

η = POUT/PIN

η = 0.54/0.62084

η = 87%

Example 2

The ADM8845 driving six white LEDs with a 20 mA/LED at

VCC = 3.4 (1.5× mode) and LED VF = 3.6 V.

PIN = ((VCC × ILOAD × Gain) + (VCC × IQ))

PIN = ((3.4 × 120 mA × 1.5) + (3.4 × 2.6 mA))

PIN = ((0.612) + (0.00884))

PIN = 0.62084

POUT = 6 × (VF × ILED)

POUT = 6 × (3.6 V × 20 mA)

POUT = 0.432

η = POUT/PIN

η = 0.432/0.62084

η = 70%

Rev. D | Page 17 of 18

Share Link: