ACE735E Datasheet, PDF (5/10 Pages) ACE Technology Co., LTD. – 36V Input Standoff Voltage, 1.5A Step-Down Converter

ACE735E
36V Input Standoff Voltage, 1.5A Step-Down Converter
FUNCTIONAL DESCRIPTIONS
Loop Operation
The ACE735E is a wide input range, high-efficiency, DC-to-DC step-down switching regulator, capable
of delivering up to 1.5A of output current, integrated with a 300mΩ high side MOSFET. It uses a PWM
current-mode control scheme. An error amplifier integrates error between the FB signal and the internal
reference voltage. The output of the integrator is then compared to the sum of a current-sense signal and
the slope compensation ramp. This operation generates a PWM signal that modulates the duty cycle of
the power MOSFETs to achieve regulation for output voltage.
Light Load Operation
Traditionally, a fixed constant frequency PWM DC-DC regulator always switches even when the output
load is small. When energy is shuffling back and forth through the power MOSFETs, power is lost due to
the finite RDSONs of the MOSFETs and parasitic capacitances. At light load, this loss is prominent and
efficiency is therefore very low. ACE735E employs a proprietary control scheme that improves efficiency
in this situation by enabling the device into a power save mode during light load,thereby extending the
range of high efficiency operation.
APPLICATION INFORMATION
Setting Output Voltages
Output voltages are set by external resistors. The FB threshold is 0.8V.
R_TOP = R_BOTTOM x [(V_OUT / 0.8) - 1]
Inductor Selection
The peak-to-peak ripple is limited to 30% of the maximum output current. This places the peak current
far enough from the minimum overcurrent trip level to ensure reliable operation while providing enough
current ripples for the current mode converter to operate stably. In this case, for 1.5A maximum output
current, the maximum inductor ripple current is 500 mA. The inductor size is estimated as following
equation:
L_IDEAL=(V_IN(MAX)-V_OUT)/I_RIPPLE*D_MIN*(1/F_OSC) Therefore, for V_OUT=5V,
The inductor values is calculated to be L = 13μH. Chose 10μH or 15μH
For V_OUT =3.3V,
The inductor values is calculated to be L = 9.2μH. Chose 10μH
Output Capacitor Selection
For most applications a nominal 22μF or larger capacitor is suitable. The ACE735E internal
compensation is designed for a fixed corner frequency that is equal to
For example, for V_OUT=5V, L=15μH, C_OUT=22μF.
The output capacitor keeps output ripple small and ensures control-loop stability. The output capacitor
must also have low impedance at the switching frequency. Ceramic, polymer, and tantalum capacitors are
suitable, with ceramic exhibiting the lowest ESR and high-frequency impedance. Output ripple with a
ceramic output capacitor is approximately as follows:
V_RIPPLE = IL_(PEAK)[1 / (2π x f_OSC x C_OUT)]
If the capacitor has significant ESR, the output ripple component due to capacitor ESR is as follows:
V_RIPPLE(ESR) = IL_(PEAK) x ESR
VER 1.1 5