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参数资料
| 型号： | MAX1913 |
| 厂商： | Maxim Integrated Products, Inc. |
| 英文描述： | 60mA 1.5x High-Efficiency White LED Charge Pumps |
| 中文描述： | 60mA的1.5倍高效率白光LED电荷泵 |
| 文件页数： | 4/11页 |
| 文件大小： | 275K |
| 代理商： | MAX1913 |
M
60mA 1.5x High-Efficiency White LED
Charge Pumps
4
_______________________________________________________________________________________
Detailed Description
The MAX1912/MAX1913 are complete charge-pump
boost converters requiring only four small ceramic
capacitors. They employ a 750kHz fixed-frequency
50% duty-cycle clock. The MAX1912/MAX1913 use a
1.5x charge- pump mode. This operation has two phas-
es (see Figure 1), charge and transfer. In charge
phase, transfer capacitors C1 and C2 charge in series
from the input voltage. In transfer phase, C1 and C2
are configured in parallel and connected from OUT to
IN, transferring charge to C
OUT
. If this system were
allowed to operate unregulated and unloaded, it would
generate an output voltage 1.5 times the input voltage.
Output Regulation
The output voltage is regulated by controlling the rate
at which the transfer capacitors are charged. The
switching frequency and duty cycle are constant, so
the output noise spectrum is predictable. Input and out-
put ripple are much smaller in value than with other
regulating charge-pump topologies because the
charge transferred per cycle is only the amount
required to supply the output load.
Soft-Start
The MAX1912/MAX1913 include soft-start circuitry to
limit inrush current at turn-on. When starting up with the
output voltage at zero, the output capacitor is charged
through a ramped current source, directly from the
input with no charge-pump action until the output volt-
age is near the input voltage. If the output is shorted to
ground, the part remains in this mode without damage
until the short is removed.
Once the output capacitor is charged to the input volt-
age, the charge-pumping action begins. Startup surge
current is minimized by ramping up charge on the
transfer capacitors. As soon as regulation is reached,
soft-start ends and the part operates normally. If the
SET voltage reaches regulation within 2048 clock
cycles (typically 2.7ms), the part begins to run in nor-
mal mode. If the SET voltage is not reached by 2048
cycles, the soft-start sequence is repeated. The
devices will continue to repeat the soft-start sequence
until the SET voltage reaches the regulation point.
Shutdown Mode
When driven low,
SHDN
turns off the charge pump.
This reduces the quiescent current to approximately
0.1μA. The output is high impedance in shutdown.
Drive
SHDN
high or connect to IN for normal operation.
Thermal Shutdown
The MAX1912/MAX1913 shut down when their die tem-
perature reaches +160
°
C. Normal operation continues
after the die cools by 15
°
C. This prevents damage if an
excessive load is applied or the output is shorted to
ground.
Design Procedure
Setting Output Current (MAX1912)
The MAX1912 has a SET voltage threshold of 0.2V,
used for LED current regulation (Figure 2). The current
through the resistor and LED is:
I
LED
= 0.2/R
If additional matching LEDs with ballast resistors are
connected to the output as in Figure 2, the current
Pin Description
PIN
1
2
3
4
5
NAME
GND
IN1
C2-
C1+
OUT
FUNCTION
Ground
Supply Voltage Input. Connect to IN2. Bypass to GND with a 2.2μF ceramic capacitor.
Transfer Capacitor 2 Connection, Negative Side
Transfer Capacitor 1 Connection, Positive Side
Output. Bypass to GND with a 2.2μF ceramic capacitor.
Shutdown Input. Drive low to turn off the device and disconnect the load from the input. OUT is high
impedance in shutdown. Drive high or connect to IN for normal operation.
Transfer Capacitor 2 Connection, Positive Side
Supply Voltage Input. Connect to IN1.
Transfer Capacitor 1 Connection, Negative Side
SET programs the output voltage with a resistive-divider from OUT (MAX1913), or programs output
current with a resistor from SET to GND (MAX1912). For the MAX1913, when SET is connected to IN,
V
OUT
is internally set to 5V.
6
SHDN
7
8
9
C2+
IN2
C1-
10
SET
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