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参数资料
| 型号： | MAX1913EUB50 |
| 厂商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分类： | 稳压器 |
| 英文描述： | 60mA 1.5x High-Efficiency White LED Charge Pumps |
| 中文描述： | 0.06 A SWITCHED CAPACITOR REGULATOR, 875 kHz SWITCHING FREQ-MAX, PDSO10 |
| 封装： | MICRO MAX PACKAGE-10 |
| 文件页数： | 5/11页 |
| 文件大小： | 275K |
| 代理商： | MAX1913EUB50 |
M
60mA 1.5x High-Efficiency White LED
Charge Pumps
_______________________________________________________________________________________
5
through each additional LED is the same as that in the
regulated LED.
In Figure 2, total LED current depends somewhat on
LED matching. Figure 3 shows a connection that regu-
lates the average of all the LED currents to reduce the
impact of mismatched LEDs. Figure 4
’
s circuit
improves LED current matching by raising the ballast
resistance while maintaining a 200mV V
SET
. The
increased ballast resistance tolerates wider LED mis-
match but reduces efficiency and raises the minimum
input voltage required for regulation.
Yet another method of biasing LEDs is shown in Figure
5. In this case, the current through the complete paral-
lel combination of LEDs is set by R4. R1, R2, and R3
are only used to compensate for LED variations. This
method of biasing is useful for parallel LED arrays that
do not allow connection to individual LEDs.
Setting Output Voltage (MAX1913)
The MAX1913 has a SET voltage threshold of 1.25V.
The output voltage is set by connecting a resistor volt-
age divider as shown in Figure 6. The output voltage is
adjustable from 3V to 5V. To set the output voltage,
select a value for R2 that is less than 50k
, then solve
for R1 using the following equation:
If SET is connected to the input, the output voltage is
5V (Figure 7). Other parts with internally set voltages
from 3V to 5V in 100mV steps are available by special
order.
Capacitor Selection
Use low-ESR ceramic capacitors. Recommended values
are 0.47μF for the transfer capacitors, 2.2μF to 10μF for
the input capacitor, and 2.2μF to 4.7μF for the output
capacitor. To ensure stability over a wide temperature
range, ceramic capacitors with an X7R dielectric are rec-
ommended. Place these capacitors as close to the IC as
possible. Increasing the value of the input and output
capacitors further reduces input and output ripple. With
a 10μF input capacitor and a 4.7μF output capacitor,
input ripple is less than 5mV peak-to-peak and output
ripple is less than 15mV peak-to-peak for 60mA of output
current. A constant 750kHz switching frequency and
fixed 50% duty cycle create input and output ripple with
a predictable frequency spectrum.
Decoupling the input with a 1
resistor (as shown in
Figures 2
–
10) will improve stability when operating from
low-impedance sources such as high-current laboratory
bench power supplies. This resistor may be omitted
when operating from higher impedance sources such
as lithium or alkaline batteries.
For some designs, such as an LED driver, input ripple
is more important than output ripple. Input ripple
depends on the source supply
’
s impedance. Adding a
lowpass filter to the input further reduces ripple. Figure
8 shows a C-R-C filter used to reduce input ripple to
less than 1mV when driving a 60mA load.
Applications Information
Adjusting LED Intensity
Figure 9 shows a circuit using a DAC to set the LED
intensity. Maximum intensity occurs when the output of
the DAC is zero. R
L
may be initially estimated from the
maximum load current:
R
L
≈
0.2/I
L(MAX)
Use this as a starting point to calculate R
A
and R
B
from
the formula below. The total load current at different
DAC output voltages is determined by:
Figure 10 uses a digital input for two-level dimming
control. The LEDs are brightest when a logic low input
(V
LOGIC
= 0) is applied, and dimmed with a logic high
input. The total LED current is determined by:
PC Board Layout
The MAX1912/MAX1913 are high-frequency switched-
capacitor voltage regulators. For best circuit perfor-
mance, use a ground plane and keep C
IN
, C
OUT
, C1,
C2, and feedback resistors (if used) close to the
device. If using external feedback, keep the feedback
node as small as possible by positioning the feedback
resistors very close to SET.
I
R
V
R
R
R
L
L
LOGIC
B
L
A
=
×
×
0 2
.
0. )
(
I
R
V
R
R
R
L
L
DAC
B
L
A
=
×
×
0 2
.
0. )
(
R
R
V
OUT
1 25
.
1
2
1
=
Chip Information
TRANSISTOR COUNT: 2500
PROCESS: BiCMOS
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