L7983 datasheet(9/43 Pages) STMICROELECTRONICS

9 / 43 page

Functional description

The L7983 device is a monolithic step-down (“buck”) DC-DC voltage regulator based on a peak current mode,

constant frequency architecture, with integrated control loop compensation network.

The main internal blocks are shown in Figure 2 and can be summarized as follows:

•

Power section, including high-side and low-side power MOSFETs, gate driver and current sensing

•

Control loop blocks, including the trans-conductor (gm), the PWM comparator and the slope generator

•

The control logic for low noise mode (LNM) or low consumption mode (LCM) operation selection and

synchronization to external clock

•

The frequency programming circuitry for device configuration

•

Input voltage monitor and enable circuit with soft-start management and RST output signal for sequencing

programming

•

The low drop-out linear regulator (LDO) and switchover block to improve the power conversion efficiency.

The fault management, including the overcurrent (OCP), the overvoltage (OVP) and overtemperature (OTP)

protection

5.1

Power section

The L7983 integrates both power MOSFETs for synchronous operation; one P-channel (high-side, HS) and one

N-channel (low-side, LS), optimized for fast switching transition and high efficiency over the entire load range. The

power stage is designed to deliver a continuous output current up to 0.3 A.

The HS MOSFET source is connected to the VIN pin, the LS MOSFET source is connected to the GND pin

(power ground). The HS MOSFET drain and LS MOSFET drain are connected together and to the LX pin (see

Figure 2).

The L7983 embodies an anti-shoot-through and adaptive deadtime control to minimize low-side body diode

conduction time and consequently reduce power losses. This feature is implemented by comparing LX with HS

and LS gate driving voltage.

•

Following the HS turn-off, the LS MOSFET is suddenly switched on as soon as the voltage at the LX pin

drops

•

Following the LS turn-off, the HS MOSFET is suddenly switched on as soon as the gate driving voltage of

LS drops

If the current flowing in the inductor is negative (i.e. from VOUT to VIN), the voltage on the LX pin can’t drop after

HS MOS turn-off. A watchdog controller is implemented to allow the LS MOSFET to turn on even in this case,

allowing the negative current of the inductor to flow to ground. This mechanism allows the system to regulate

even if the current is negative (if LNM mode is enabled).

5.2

Control loop and voltage programming

The L7983 is based on a constant frequency peak current mode architecture.

Thanks to integrated compensation network and slope generation, no additional external components are

necessary for loop stabilization.

L7983

Functional description

DS13354 - Rev 1

page 9/43

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