EVALA5970D STMicroelectronics, EVALA5970D Datasheet - Page 8

• Manufacturer Part Number: EVALA5970D
• Description: Power Management Modules & Development Tools EVAL BOARD A5970D Auto Grade
• Manufacturer: STMicroelectronics
• Type: DC/DC Switching Converters, Regulators & Controllersr

Specifications of EVALA5970D

• Input Voltage: 4.4 V to 36 V
• Output Voltage: 1.235 V to 35 V
• Board Size: 23 mm x 20 mm
• Product: Power Management Modules
• Supply Current: 1 A
• Dimensions: 23 mm x 20 mm
• For Use With/related Products: AN1330
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Functional description
2.4
2.5
8/31
Figure 6.
Current protection
The L5970D has two types of current limit protection: pulse-by-pulse and frequency
foldback.
The schematic of the current limitation circuitry for the pulse-by-pulse protection is shown in
Figure
The smallest one includes a resistor in series, R
R
switched off until the next falling edge of the internal clock pulse. Due to this reduction of the
ON time, the output voltage decreases. Since the minimum switch ON time (necessary to
avoid a false overcurrent signal) is too short to obtain a sufficiently low duty cycle at 250
kHz, the output current, in strong overcurrent or short circuit conditions, could increase
again. For this reason the switching frequency is also reduced, thus keeping the inductor
current under its maximum threshold. The Frequency Shifter
the feedback voltage. As the feedback voltage decreases (due to the reduced duty cycle),
the switching frequency decreases also.
Figure 7.
Error amplifier
The voltage error amplifier is the core of the loop regulation. It is a transconductance
operational amplifier whose non inverting input is connected to the internal voltage
SENSE
7. The output power PDMOS transistor is split into two parallel PDMOS transistors.
and if reaches the threshold, the mirror becomes unbalanced and the PDMOS is
Oscillator circuit block diagram
Current limitation circuitry
A1/A2=95
DRIVER
VCC
OUT
Ibias_osc
FREQUENCY
I
GENERATOR
OFF
FREQUENCY
GENERATOR
SHIFTER
SHIFTER
CLOCK
CLOCK
PWM
A1
RSENSE
SYNCHRONIZATOR
A2
SENSE
SYNCHRONIZER
GENERATOR
GENERATOR
RAMP
RAMP
. The current is sensed through
I
(Figure
I
CLOCK
RAMP
SYNC
NOT
AM00008v1
6) functions based on
t
RTH
I
L
AM00007v1
AN1330