APW7128QA 查看數據表（PDF） - Anpec Electronics

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APW7128QA

30V, 1.2MHz, White LED Driver

Anpec Electronics 

APW7128

Function Description

Output Over-Voltage Protection

If the FB pin is shortened to the ground or an LED fails

open circuit, output voltage in BOOST mode can increase

to potentially damaging voltages. An optional over-volt-

age protection circuit can be enabled by connection of

the OVP pin to the output voltage. The device will stop

switching if the output voltage exceeds OVP high thresh-

old and re-start when the output voltage falls below OVP

low threshold. During sustained OVP fault conditions,

VOUT will saw-tooth between the upper and lower thresh-

old voltages at a frequency determined by the magnitude

of current available to discharge the output capacitor. Note

that the OVP pin must be connected to output voltage for

OVP function.

Ambient Light Sensor Interface

The APW7128 provides the ALS pin to simplify the inter-

face to an ambient light sensor. The ambient light sensor

detects the ambient light and yields a current which is

related to the illuminance. Connect a load resistor from

the current output of ambient light sensor to ground to

provide an output voltage to ALS pin. The ALS voltage will

be divided by an internal divider circuit, and the divided

ALS voltage will replace the internal reference voltage.

The LED current can be calculated by the following

equation:

ILED

=

1

3

×

VALS

R1

Note that the maximum FB voltage is set to 0.5V, and

minimum FB voltage is set to 0.2V. If the divided ALS

voltage is over 0.5V or less 0.2V, the LED current is lim-

ited at:

ILED(MAX)

=

0.5V

R1

ILED(MIN)

=

0.2V

R1

where R1 is the resistor from FB to GND.

Thermal Shutdown

When the junction temperature exceeds 150°C, the inter-

nal thermal sensor circuit will disable the device and al-

low the device to cool down. When the device’s junction

temperature cools by 50°C, the internal thermal sense

circuit will enable the device, resulting in a pulsed output

during continuous thermal protection. Thermal protec-

tion is designed to protect the IC in the event of over tem-

perature conditions. For normal operation, the junction

temperature cannot exceed TJ=+125 °C.

Internal 5V LDO

The APW7128 provides an internal 5V LDO for the control

circuitry, and the output of the internal LDO is BP pin. In

normal operation, connect a 1µF or greater capacitor to

GND is recommended. The internal LDO cannot supply

any more current than is required to operate the APW7128.

Therefore, do not apply any external load to BP pin. In

applications, where the V is less than 5.5V, BP should

IN

be tied to VIN through a 10Ω resistor.

Enable/Disable

Pull the EN above 2V to enable the device and pull EN pin

below 0.4V to disable the device. In shutdown mode, the

internal control circuits are turned off, the quiescent cur-

rent is below 1µA.

Copyright © ANPEC Electronics Corp.

9

Rev. A.2 - Aug., 2010

www.anpec.com.tw

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