The EL7532 is a synchronous integrated FET2A buck regulator with internal compensation. It works with an input voltage range of 2.5V~5.5V, suitable for 3.3V, 5V power supplies, or lithium-ion batteries. The output can be set externally via a resistive divider in the range of 0.8V to VIN.

The main feature of EL7532 is PWM mode control. The typical value of its operating frequency is 1.5MHz. Other features include 100ms power-on reset output, less than 1µA shutdown current, short-circuit protection and thermal protection.

startup and shutdown

The regulator starts switching when the EN pin is connected to VIN and VIN reaches about 2.4V. This output voltage is gradually increased to ensure proper soft-start operation. When the EN pin is connected to a logic low level, the EL7532 is in shutdown mode. All control circuits and both MOSFETs are cut off and VOUT drops to zero. In this mode, the total input current is less than 1µA. When EN reaches a logic high level, the regulation repeats the start-up procedure, including the soft-start function.

typical application

PWM working mode

In PWM mode, the P-channel MOSFET and N-channel MOSFET are usually complementary. The inductor current increases linearly when a PMOSFET is used as an upper and NMOS FET. The input energy is transferred to the output and also stored in the inductor. When the P-channel MOSFET turns on and off, the inductor's N-channel MOSFET current decreases linearly, and energy is diverted from the output of the inductor. Therefore, the average current through the inductor is the output current. Since the inductor and output capacitor act as a low-pass filter, the duty cycle ratio is approximately equal to VO divided by VIN. The output LC filter has a second-order effect. To maintain converter stability, the overall controller must compensate. This is the same as the error amplifier and PWM compensator which do fixed compensation internally. Because the compensation is fixed, the value of the input and output capacitors are 10µF and 22µF ceramic. The nominal value of this inductor is 1.8μH, although 1.5μH can be used as 2.2μH.

100% duty cycle operation The EL7532 uses a CMOS power field effect transistor as an internal synchronous power switch. The upper switch is PMOS and the lower switch is NMOS. This not only saves the boot capacitor, but also can turn on the switch of the upper PFET 100%, so that VO is close to VIN. The maximum achievable VO is, VO=VIN–(RL+RDSON1)×IO where RL is the DC resistance of the inductor and R DSON1PFET on-resistance, nominally 70mΩ at room temperature with a temperature coefficient of 0.2mΩ/°C content. As the input voltage gradually drops close to or even below the preset VO, the converter enters a 100% duty cycle. Under this condition, the upper PFET needs a certain minimum off time if it is turned off. This off-time is related to input/output conditions. This makes the duty cycle random and increases the output ripple somewhat until 100% duty cycle is reached. Larger output capacitors can reduce random-finding ripple. The user needs to verify if this condition has an adverse effect on the overall circuit and if close to 100% duty cycle is expected.

RSI/POR function When powered on, the open collector power-on resets about 100ms after the V output remains low and O reaches the preset voltage. When the active hi reset signal RSI is issued, POR immediately becomes low level, and after saving the time of RSI, it returns to low level in the same period. This output voltage is not affected. When this function is not being used, connect RSI to ground and leave room for a pull-up resistor ~4 on the POR pin. The power-on reset output also acts as a 100ms delayed power good signal when a pull-up resistor ~4 is installed. The RSI pin needs to be connected directly (or indirectly through a resistor R6) to ground for it to work properly.

Timing diagram

Current Limit and Short Circuit Protection

The current limit is set to about 3A for PMOS. When a short circuit occurs at the load, the preset current limit limits the amount currently available to output, which drops the output voltage below the predetermined voltage. During this time, the excess current heats the regulator until the thermal shutdown point is reached.

thermal shutdown

Once the junction temperature reaches 145°C, the regulator shuts down. Both P-channel and N-channel MOSFETs are turned on and off. The output voltage will drop to zero. With the output MOSFET turned off, the regulator will cool down quickly. Once the junction temperature drops to about 130°C, the regulator will restart again in the same way the EN pin is tied to a logic high.

Thermal performance

The EL7532 is in a molten lead MSOP10 package. Compared to the regular MSOP10 package, this fused lead package offers lower thermal resistance. A typical θJA of 115°C/W improves the pin by maximizing the surrounding copper area. A θJA at 100°C/W can be achieved on a four-layer board and 125°C/W on a 2-layer substrate.

pin