L5988D datasheet(12/52 Pages) STMICROELECTRONICS

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Functional description

L5988D

12/52

DocID15324 Rev 4

Functional description

The L5988D is based on a voltage mode control loop. Therefore the duty ratio of the internal

switch is obtained through a comparison between a saw-tooth waveform (generated by an

oscillator) and the output voltage of the error amplifier as shown in Figure 3. The advantage

of this technique is the very short conduction time of the power elements thanks to the

proper operation of the control loop without a precise current sense, which instead is

required in current mode regulators. Thanks to this architecture the L5988D supports

extremely low conversion ratio (D = VOUT/VIN) even at very high switching frequency

(up to 1 MHz).

Figure 3. Voltage mode control loop

The main internal blocks are represented in Figure 4.

Figure 4. Internal block diagram

REF

E/A

PWM

VOUT

OSCILLATOR RAMP

REF

E/A

PWM

VOUT

OSCILLATOR RAMP

REF

E/A

PWM

VOUT

OSCILLATOR RAMP

REF

E/A

PWM

VOUT

OSCILLATOR RAMP

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