L5981 STMicroelectronics, L5981 Datasheet - Page 7

• Manufacturer Part Number: L5981
• Description: IC REG SW STEP DOWN 1A 8-VFQFPN
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L5981

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 0.6 ~ 18 V
• Current - Output: 1A
• Frequency - Switching: 250kHz ~ 1MHz
• Voltage - Input: 2.9 ~ 18 V
• Operating Temperature: -40°C ~ 125°C
• Mounting Type: Surface Mount
• Package / Case: 8-VFQFN, 8-VFQFPN
• Power - Output: 1.5W
• Output Voltage: 3 V
• Output Current: 1 A
• Input Voltage: 2.9 V to 18 V
• Switching Frequency: 220 KHz to 275 KHz
• Operating Temperature Range: - 40 C to + 150 C
• Mounting Style: SMD/SMT
• Duty Cycle (max): 100 %
• Low Dropout Operation: 100 % duty cycle
• For Use With: 497-6385 - BOARD EVAL FOR L5981
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

L5981
4
Functional description
The L5981 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 and 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 13004 Rev 6
Figure
3. They are:
Functional description
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