The EL7530 is a synchronous integrated FET 600 mA step-down regulator with internal compensation. It has an input voltage range of 2.5V to 5.5V, which can accommodate 3.3V, 5V or Li-Ion battery supply sources. The output can be set externally at 0.8V to VIN with a resistor divider. The EL7530 has automatic PFM/PWM mode control, or only PWM mode. The PWM frequency is 1.4MHz typical and can be synchronized to 12MHz. Typical no-load quiescent current is only 120µA. Other features include a power good output, <1µA shutdown current, short circuit protection and over temperature protection. The EL7530 is available in a 10-pin MSOP package, so that the entire converter occupies less than 0.18N2of PCB area with components on only one side. The 10-pin MSOP package is specified over the -40°C to +85°C temperature range.

Typical application diagram

PFM operation

The heart of the EL7530 regulator is the automatic PFM/PWM controller. If the SYNC pin is connected to ground, the regulator operates automatically in either PFM mode or PWM mode, depending on the load. When the SYNC pin is connected to VIN, the regulator operates in fixed PWM mode. When the pin is connected to an external clock ranging from 1.6MHz to 12MHz, the regulator is in fixed PWM mode, synchronized to the external clock frequency. In PFM/PWM automatic operation, when the load is small, the regulator works in PFM mode to achieve high efficiency. The top P-channel MOSFET is turned on first. It is turned off before the inductor current increases linearly to the preset value. Then the lower N-channel MOSFET turns on, and the inductor current decreases linearly to zero current. The N-channel MOSFET is turned off again, and the anti-ring MOSFET is turned on by tweezing the VLX pin to VO. The inductor current looks like a triangular pulse. The frequency of this pulse is primarily a function of the output current. The higher the load of the pulse, the higher the frequency until the inductor current becomes continuous. At this point, the controller automatically switches to PWM operation.

PWM working mode

The regulator works in the same way in forced PWM or synchronous PWM mode. In this mode, the inductor current is always continuous and never stops at zero. In this way, the P-channel MOSFET and the 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 inductors are 1.5µH to 2.2µH.

Current Limit and Short Circuit Protection

The current limit is set at around 1.2A for the 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 a predetermined voltage. During this time, the excess current heats the regulator until the thermal shutdown point is reached.

block diagram