ADP1655 Analog Devices, ADP1655 Datasheet - Page 21

• Manufacturer Part Number: ADP1655
• Description: Dual LED Flash Driver with I2C Compatible Interface
• Manufacturer: Analog Devices

Specifications of ADP1655

• Product Description: Serial 2 WLED Flash Driver
• Led #: 2
• Led Configuration: Serial
• Topology: Inductive
• Application: Flash
• I2c Support: Yes
• Max Iout (ma): 400mA
• Brightness Control: I2C
• Peak Efficiency (%): n/a
• Switching Frequency: 2MHz
• Over Volt Protection (v): 10V
• Vin Min (v): 2.5V
• Vout (v): Current Output
• Synchronous: Yes
• Package: 12-Bump WLCSP

The worst-case capacitance accounting for capacitor variation
over temperature, component tolerance, and voltage is calcu-
lated using the following equation:
where:
C
TEMPCO is the worst-case capacitor temperature coefficient.
TOL is the worst-case component tolerance.
In this example, TEMPCO over −40°C to +85°C is assumed to
be 15% for an X5R dielectric, TOL is assumed to be 10%, and
C
Substituting these values in the equation yields
EFF
OUT
Figure 35. DC Bias Characteristic of a 16 V, 10 μF Ceramic Capacitor
is the effective capacitance at the operating voltage.
C
C
is 9.528 μF at 1.8 V, as shown in Figure 35.
EFF
EFF
12
10
8
6
4
2
0
= C
= 9.528 μF × (1 − 0.15) × (1 − 0.1) = 7.288 μF
0
OUT
2
× (1 − TEMPCO) × (1 − TOL)
4
DC BIAS VOLTAGE (V)
6
8
10
12
14
16
Rev. 0 | Page 21 of 24
To guarantee the performance of the ADP1655, it is imperative
that the effects of dc bias, temperature, and tolerances on the
behavior of the capacitors be evaluated for each application.
The peak-to-peak output voltage ripple for the selected output
capacitor and inductor values is calculated using the following
equation:
Capacitors with lower equivalent series resistance (ESR) are
preferred to guarantee low output voltage ripple, as shown in
the following equation:
The effective capacitance needed for stability, which includes
temperature and dc bias effects, is 4 μF.
V
ESR
RIPPLE
COUT
=
≤
(
2
V
π
I
RIPPLE
RIPPLE
×
f
SW
)
V
×
IN
2
×
L
×
C
OUT
=
8
×
f
I
SW
RIPPLE
ADP1655
×
C
OUT