MAX1575(2003) Ver la hoja de datos (PDF) - Maxim Integrated
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MAX1575 Datasheet PDF : 9 Pages
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White LED 1x/1.5x Charge Pump
for Main and Sub-Displays
Pin Description
PIN
NAME
FUNCTION
1
C2P Transfer-Capacitor 2 Positive Connection. Connect a 1µF ceramic capacitor from C2P to C2N.
2
OUT
Output. Connect a 1µF ceramic capacitor from OUT to GND. Connect OUT to the anodes of all the LEDs.
OUT is internally pulled down with 5kΩ during shutdown.
3
SET
Current-Set Input. Connect a resistor (RSET) from SET to GND to set the maximum LED current. ILED(MAX) =
228 × 0.6V / RSET. SET is internally biased to 0.6V. SET is high impedance during shutdown.
Enable and Dimming Control for LED5 and LED6 (Sub-Display). The first time ENS goes high (50µs min),
LED5 and LED6 turn on at 100% brightness. Pulsing ENS low dims the LEDs in multiple steps. If ENS is held
4
ENS low for more than 2ms (typ), LED5 and LED6 turn off. When ENM and ENS are both held low for more than
2ms (typ), the IC goes into shutdown mode. See Figure 1.
Enable and Dimming Control for LED1–LED4 (Main Display). The first time ENM goes high (50µs min),
LED1–LED4 turn on at 100% brightness. Pulsing ENM low dims the LEDs in multiple steps. If ENM is held low for
5
ENM more than 2ms (typ), LED1–LED4 turn off. When ENM and ENS are both held low for more than 2ms (typ), the IC
goes into shutdown mode. See Figure 1.
6
LED6 Sub-Display LEDs Cathode Connection. Current flowing into LED_ is described in the ENS and SET
descriptions above. The charge pump regulates the lowest-enabled LED_ voltage to 180mV. Connect LED_
7
LED5 to IN if the LED is not populated. LED_ is high impedance during shutdown.
8
LED4
9
LED3 Main-Display LEDs Cathode Connection. Current flowing into LED_ is described in the ENM and SET
descriptions above. The charge pump regulates the lowest-enabled LED_ voltage to 180mV. Connect LED_
10
LED2 to IN if the LED is not populated. LED_ is high impedance during shutdown.
11
LED1
12
GND
Ground. Connect GND as close as possible to system ground and to the ground of the input bypass
capacitor.
13
C1N Transfer-Capacitor 1 Negative Connection. Connect a 1µF ceramic capacitor from C1P to C1N.
14
IN
Supply Voltage Input. Connect a 1µF ceramic capacitor from IN to GND. The input voltage range is 2.7V to
5.5V. IN is high impedance during shutdown.
15
C2N Transfer-Capacitor 2 Negative Connection. Connect a 1µF ceramic capacitor from C2P to C2N.
16
C1P Transfer-Capacitor 1 Positive Connection. Connect a 1µF ceramic capacitor from C1P to C1N.
—
EP Exposed Paddle. Connect the exposed paddle to GND.
Detailed Description
The MAX1575 charge pump drives up to four white
LEDs in the main display and up to two white LEDs in
the sub-display with regulated constant current for
uniform intensity. By utilizing adaptive 1x/1.5x charge-
pump modes and very-low-dropout current regulators, it
achieves high efficiency over the 1-cell lithium-battery
input voltage range. 1MHz fixed-frequency switching
allows for tiny external components and low input ripple.
1x to 1.5x Switchover
When VIN is higher than VOUT, the MAX1575 operates in
1x mode and VOUT is pulled up to VIN. The internal cur-
rent regulators regulate the LED current. As VIN drops,
VLED_ eventually falls below the switchover threshold of
100mV and the MAX1575 starts switching in 1.5x mode.
When the input voltage rises above VOUT by about 50mV,
the MAX1575 switches back to 1x mode.
Soft-Start
The MAX1575 includes soft-start circuitry to limit inrush
current at turn-on. When starting up, the output capacitor
is charged directly from the input with a ramped current
source (with no charge-pump action) until the output volt-
age approaches 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. During the soft-start time, the
output current is set to 5% of the maximum set by RSET.
In the case of 1.5x mode, soft-start operates until the low-
est of LED1–LED6 reaches regulation. If an overload con-
dition occurs, soft-start repeats every 2ms. If the output is
shorted to ground (or <1.25V), the part reverts to soft-
start and the ramped current source.
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