ACE716E

Max 38V, Variable Frequency Step-up DC/DC Converter

VER 1.1

7

FUNCTIONAL DECRIPTIONS

The ACE716E is a high efficiency boost LED driver with a small package size. The device is ideal for

driving 2-25LEDs for backlight application in smartphone and 7-inch tablet PC. The device integrates a

38V/1A switch FET and operates in pulse width modulation (PWM) with a 0.8MHz fixed switching

frequency. For operation details, please check the block diagram in the “Block Diagram” chapter. The duty

cycle of the converter is set by the error amplifier output and the current

signal applied to the PWM

control comparator. The feedback

loop regulates the FB pin to a low reference

voltage (200mV typical),

reducing the power dissipation in the current

sense resistor.

Output Open Circuit Protection

Output open circuit protection circuitry prevents IC damage as the result of output open circuit (e.g. LED

string absence). The ACE716E monitors the voltage at the SW pin and FB pin during each switching

cycle. The circuitry turns off the switch FET and shuts down the IC when both of the following conditions

persist for 8 switching clock cycles: (1) the SW voltage exceeds the VOVP threshold, which is 38V and (2)

the FB voltage is less than half of regulation voltage. As a result, the output voltage falls to the level of the

input supply. The device remains in shutdown mode until it is enabled by toggling the EN pin logic. The

output voltage plus the 200mV reference voltage cannot exceed the minimum OVP threshold or OUTPUT

VOLTAGE + 200 mV ≤ VOVP(MIN).

Shutdown

The ACE716E enters shutdown mode when the EN voltage is logic low for more than 3ms. During

shutdown, the input supply current for the device is less than 1μA (max). Although the internal FET does

not switch in shutdown, there is still a DC current path between the input and the output through the

inductor and Schottky diode.

For LED driving application, the minimum forward voltage of the LED array must exceed the maximum

input voltage to ensure that the LEDs remain off in shutdown. However, in the typical application with two

or more LEDs, the forward voltage is large enough to reverse bias the Schottky and keep leakage current

low.

LED Driving Current Setting

The FB voltage is regulated by a low 0.2V reference voltage. The LED current is set externally using a

current-sense resistor in series with the LED string. The value of the RSET is calculated using Equation

1.2:

ILED =0.2/RSET

(1.2)

Where

ILED = output current of LEDs, RSET = current sense resistor

The output current tolerance depends on the FB accuracy and the current sensor resistor accuracy.

PWM Dimming Control or Output Voltage Programming

When the CTRL pin is constantly high, the FB voltage is regulated to 200mV typically. However, the EN

pin allows a PWM signal to reduce this regulation voltage; therefore, it achieves LED brightness dimming

or output voltage programming (only to make output voltage lower). The relationship between the duty

cycle and FB voltage is given by Equation 2.