SNVSB97A December 2018 – September 2021 LM34936-Q1
The LM34936-Q1 is a wide input voltage four-switch buck-boost controller IC with integrated drivers for N-channel MOSFETs. It operates in Buck mode when VIN is greater than VOUT and in Boost mode when VIN is less than VOUT. When VIN is close to VOUT, the device operates in a proprietary transition Buck or Boost mode. The control scheme provides smooth operation for any input/output combination within the specified operating range. The buck or boost transition control scheme provides a low ripple output voltage when VIN equals VOUT without compromising the efficiency.
The LM34936-Q1 integrates four N-channel MOSFET drivers including two low-side drivers and two high-side drivers, eliminating the need for external drivers or floating bias supplies. The internal VCC regulator supplies internal bias rails as well as the MOSFET gate drivers. The VCC regulator is powered either from the input voltage through the VIN pin or from the output or an external supply through the BIAS pin for improved efficiency.
The PWM control scheme is based on valley current mode control for buck operation and peak current mode control for boost operation. The inductor current is sensed through a single sense resistor in series with the low-side MOSFETs. The sensed current is also monitored for cycle-by-cycle current limit. The behavior of the LM34936-Q1 during an overload condition is dependent on the MODE pin programming (see Section 7.4.2). If hiccup mode fault protection is selected, the controller turns off after a fixed number of switching cycles in cycle-by-cycle current limit and restarts after another fixed number of clock cycles. Hiccup mode reduces the heating in the power components in a sustained overload condition. If Hiccup mode is disabled through the MODE pin, the controller remains in a cycle-by-cycle current limit condition until the overload is removed.
In addition to the cycle-by-cycle current limiting, the LM34936-Q1 also provides an optional average current regulation loop that can be configured for either input or output current limiting. This is useful for battery charging or other applications where a constant current behavior can be required.
The soft-start time of LM34936-Q1 is programmed by a capacitor connected to the SS pin to minimize the inrush current and overshoot during start-up.
The precision EN/UVLO pin supports programmable input undervoltage lockout (UVLO) with hysteresis. The output overvoltage protection (OVP) feature turns off the high-side drivers when the voltage at the FB pin exceeds the output overvoltage threshold (VOVP). The PGOOD output indicates when the FB voltage is inside the PGOOD regulation window centered at VREF.