L5987 STMicroelectronics, L5987 Datasheet - Page 8

• Manufacturer Part Number: L5987
• Description: IC REG STEPDOWN 3A 8VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L5987

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 V ~ 18 V
• Current - Output: 3A
• Frequency - Switching: 250kHz
• Voltage - Input: 2.9 V ~ 18 V
• Operating Temperature: -40°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 8-VFQFN, Exposed Pad
• Output Voltage: 0.6 V
• Output Current: 3 A
• Output Power: 1.5 W
• Input Voltage: 2.9 V to 18 V
• Switching Frequency: 250 KHz
• Mounting Style: SMD/SMT
• Duty Cycle (max): 100 %
• Low Dropout Operation: 100 % duty cycle
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Functional description
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Functional description
The L5987 is based on a “voltage mode”, constant frequency control. The output voltage
V
an error signal that, compared to a fixed frequency sawtooth, controls the on and off time of
the power switch.
The main internal blocks are shown in the block diagram in
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Figure 3.
OUT
A fully integrated oscillator that provides sawtooth to modulate the duty cycle and the
synchronization signal. Its switching frequency can be adjusted by an external resistor.
The voltage and frequency feed forward are implemented.
The soft-start circuitry to limit inrush current during the start up phase.
The voltage mode error amplifier
The pulse width modulator and the relative logic circuitry necessary to drive the internal
power switch.
The High-side driver for embedded P-channel power MOSFET switch.
The peak current limit sensing block, to handle over load and short circuit conditions.
A voltage regulator and internal reference. It supplies internal circuitry and provides a
fixed internal reference.
A voltage monitor circuitry (UVLO) that checks the input and internal voltages.
A thermal shutdown block, to prevent thermal run away.
is sensed by the feedback pin (FB) compared to an internal reference (0.6 V) providing
Block diagram
Doc ID 14972 Rev 3
Figure
3. They are:
L5987