MAX1573 查看數據表（PDF） - Maxim Integrated
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MAX1573 Datasheet PDF : 9 Pages
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White LED 1x/1.5x Charge Pump in
UCSP and Thin QFN
Pin Description (continued)
PIN
TQFN UCSP
13
D1
14
C1
15
B1
16
A1
NAME
FUNCTION
C1N
IN
C2N
C1P
Transfer Capacitor 1 Negative Connection. See the Component Selection section for capacitor value.
Supply Voltage Input. IN supplies power for the IC. Bypass IN to GND with a 1µF ceramic capacitor.
Transfer Capacitor 2 Negative Connection. See the Component Selection section for capacitor value.
Transfer Capacitor 1 Positive Connection. See the Component Selection section for capacitor value.
Block Diagram
C1P C1N
C2P C2N
IN
OUT
1x/1.5x REGULATED CHARGE PUMP
EN1
EN2
P
0.15V
BRIGHTNESS
CONTROL
0.6V
P
N
SET
MAX1573
1.25V
MINIMUM
SELECT
LDO CURRENT
LED1
REGULATOR
LDO CURRENT
LED2
REGULATOR
LDO CURRENT
LED3
REGULATOR
LDO CURRENT
LED4
REGULATOR
GND
Detailed Description
The MAX1573 is a complete charge-pump buck-boost
converter requiring only four small ceramic capacitors.
The MAX1573 utilizes a proprietary 1x/1.5x fractional
charge-pump topology to drive up to four white LEDs
with regulated constant current for uniform intensity.
The MAX1573 operates with a 1MHz fixed frequency.
An external resistor (RSET) programs the full-scale LED
current, while two digital inputs control on/off and pro-
vide brightness control.
Output Regulation
The MAX1573 operates in 1x mode until just above
dropout. Then the MAX1573 switches to 1.5x charge-
pump mode to regulate the lowest of LED1–LED4 to
150mV and maintain constant LED brightness even at
very low battery voltages. Using this topology, there is
no LED brightness change during the 1x/1.5x switchover,
which guarantees no flicker on the display. The
switchover scheme has low hysteresis, minimizing
operation in the less-efficient 1.5x mode. The 1x mode
produces almost no ripple, while the 1.5x mode regu-
lates the output voltage by controlling the rate at which
the transfer capacitors are charged. In this way, the
switching frequency remains constant for reduced input
ripple and stable noise spectrum.
Soft-Start
The MAX1573 includes soft-start circuitry to limit inrush
current at turn-on. When starting up with an output
voltage that is not near the input voltage, the output
capacitor is charged directly from the input with a DAC-
ramped current source (with no charge-pump action)
until the output voltage is near the input voltage. Once
this occurs, the charge pump determines if 1x or 1.5x
mode is required. In the case of 1x mode, the soft-start
is terminated and normal operation begins. In the case
of 1.5x mode, soft-start operates until the lowest of
LED1–LED4 reaches regulation. If an overload condi-
tion occurs, soft-start repeats every 2.1ms. If the output
is shorted to ground, the output current is limited by
the MAX1573 fractional-switching technique.
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