L5973AD STMicroelectronics, L5973AD Datasheet - Page 8

• Manufacturer Part Number: L5973AD
• Description: IC REG SW 2A STEPDOWN 8-SOIC
• Manufacturer: STMicroelectronics
• Type: Step-Down (Buck)r

Specifications of L5973AD

• Internal Switch(s): Yes
• Synchronous Rectifier: No
• Number Of Outputs: 1
• Voltage - Output: 1.24 ~ 35 V
• Current - Output: 2A
• Frequency - Switching: 500kHz
• Voltage - Input: 4 ~ 36 V
• Operating Temperature: -40°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (3.9mm Width) Exposed Pad, 8-eSOIC. 8-HSOIC
• Power - Output: 2.25W
• Output Voltage: 35 V
• Output Current: 2 A
• Input Voltage: 4 V to 36 V
• Switching Frequency: 500 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: 497-4134 - EVAL BOARD FOR L5973 SERIES497-4133 - EVAL BOARD FOR L5973 SERIES
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Other names: 497-1417-5; 497-1417-5; 497-4565-5; E-L5973AD

Functional description
4.1
4.2
4.3
8/22
Power supply and voltage reference
The internal regulator circuit (shown in
voltage pre-regulator, the Bandgap voltage reference and the Bias block that provides
current to all the blocks.
The Starter gives the start-up currents to the whole device when the input voltage goes high
and the device is enabled (inhibit pin connected to ground).
The pre-regulator block supplies the Bandgap cell with a pre-regulated voltage V
has a very low supply voltage noise sensitivity.
Voltages monitor
An internal block senses continuously the V
their thresholds, the regulator starts to work. There is also an hysteresis on the V
Figure 4.
Oscillator and synchronization
Figure 5
The clock generator provides the switching frequency of the device that is internally fixed at
500 kHz. The frequency shifter block acts reducing the switching frequency in case of strong
overcurrent or short circuit. The clock signal is then used in the internal logic circuitry and is
the input of the ramp generator and synchronization blocks.
The ramp generator circuit provides the sawtooth signal, used to realize the PWM control
and the internal voltage feed forward, while the Synchronization circuit generates the
synchronization signal. In fact the device has a synchronization pin that can works both as
Master and Slave.
As Master to synchronize external devices to the internal switching frequency.
As Slave to synchronize itself by external signal.
shows the block diagram of the oscillator circuit.
Internal regulator circuit
D00IN1126
STARTER
V
CC
Doc ID 9552 Rev 9
Figure
IC BIAS
CC
4) consists of a start-up circuit, an internal
, V
ref
and V
PREREGULATOR
bg
. If the voltages go higher than
BANDGAP
VREG
VREF
CC
REG
L5973AD
(UVLO).
that