ADM8845EB-EVALZ Analog Devices Inc, ADM8845EB-EVALZ Datasheet - Page 17

• Manufacturer Part Number: ADM8845EB-EVALZ
• Description: BOARD EVALUATION FOR ADM8845
• Manufacturer: Analog Devices Inc

Specifications of ADM8845EB-EVALZ

• Current - Output / Channel: 20mA
• Outputs And Type: 6, Non-Isolated
• Voltage - Output: 5.5 V
• Features: Charge Pump, Dimmable
• Voltage - Input: 2.6 ~ 5.5V
• Utilized Ic / Part: ADM8845
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

POWER EFFICIENCY
The ADM8845 power efficiency (η) equations are
where:
I
V
Gain is equal to the charge pump mode (1
3.4V
Examples 1 and 2 show calculations of the ADM8845 power
efficiency. See Figure 34 as well.
Q
F
R
is the quiescent current of the ADM8845, 2.6 mA.
is the LED forward voltage.
SET
V
η = P
P
P
I
IN
CC
IN
OUT
= ((V
= 6 × (V
OUT
V
CTRL1
CTRL2
I
SET
Figure 34. Charge Pump Power Efficiency Diagram
CC
/P
CC
ADM8845
IN
× I
GND
F
LOAD
× I
LED
V
× Gain) + (I
FB1
FB2
FB3
FB4
FB5
FB6
OUT
)
I
LOAD
Q
× V
CC
×
))
, 1.5
×
, 2
×
).
Rev. C | Page 17 of 20
Example 1
The ADM8845 driving six white LED with 20 mA/LED at
V
P
P
P
P
P
P
P
η = P
η = 0.54/0.62084
η = 87%
Example 2
The ADM8845 driving six white LED with 20 mA/LED at
V
P
P
P
P
P
P
P
η = P
η = 0.432/0.62084
η = 70%
IN
IN
IN
IN
OUT
OUT
OUT
IN
IN
IN
IN
OUT
OUT
OUT
CC
CC
= ((V
= ((3.4 × 120 mA × 1.5) + (3.4 × 2.6 mA))
= ((0.612) + (0.00884))
= 0.62084
= ((V
= ((3.4 × 120 mA × 1.5) + (3.4 × 2.6 mA))
= ((0.612) + (0.00884))
= 0.62084
= 3.4 V (1.5× mode), LED V
= 3.4 (1.5× mode), LED V
= 6 × (V
= 6 × (4.5V × 20 mA)
= 0.54
= 6 × (V
= 6 × (3.6 V × 20 mA)
= 0.432
OUT
OUT
/P
/P
CC
CC
IN
IN
× I
× I
F
F
LOAD
LOAD
× I
× I
LED
LED
× Gain) + (V
× Gain) + (V
)
)
F
CC
CC
= 3.6 V.
F
× I
× I
= 4.5 V.
Q
Q
))
))
ADM8845