STEVAL-ISA026V1 STMicroelectronics, STEVAL-ISA026V1 Datasheet - Page 21

• Manufacturer Part Number: STEVAL-ISA026V1
• Description: EVAL BOARD 20A 250KHZ L6732
• Manufacturer: STMicroelectronics
• Type: DC/DC Switching Converters, Regulators & Controllersr

Specifications of STEVAL-ISA026V1

• Design Resources: STEVAL-ISA026V1 Gerber Files STEVAL-ISA026V1 Schematic STEVAL-ISA026V1 Bill of Material
• Main Purpose: DC/DC, Step Down
• Outputs And Type: 1, Non-Isolated
• Voltage - Output: 3.3V
• Current - Output: 20A
• Voltage - Input: 4.5 ~ 14V
• Regulator Topology: Buck
• Frequency - Switching: 250kHz
• Board Type: Fully Populated
• Utilized Ic / Part: L6732
• Input Voltage: 4.5 V to 14 V
• Output Voltage: 3.3 V
• Product: Power Management Modules
• Silicon Manufacturer: ST Micro
• Silicon Core Number: L6732
• Kit Application Type: Power Management - Voltage Regulator
• Rohs Compliant: No
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Power - Output: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant
• For Use With/related Products: L6732
• Other names: 497-5869

L6732
5.12
5.12.1
Bootstrap anti-discharging system
This built-in system avoids that the voltage across the bootstrap capacitor becomes less
than 3.3 V. An internal comparator senses the voltage across the external bootstrap
capacitor keeping it charged, eventually turning-on the low-side MOSFET for approximately
200 ns. If the bootstrap capacitor is not enough charged the high-side MOSFET cannot be
effectively turned-on and it will present a higher R
also triggered. The bootstrap capacitor can be discharged during the soft-start in case of
very long soft-start time and light loads. It's also possible to mention one application
condition during which the bootstrap capacitor can be discharged:
Fan's power supply
In many applications the FAN is a DC MOTOR driven by a voltage-mode DC/DC converter.
Often only the speed of the MOTOR is controlled by varying the voltage applied to the input
terminal and there's no control on the torque because the current is not directly controlled.
In order to vary the MOTOR speed the output voltage of the converter must be varied. The
L6732 has a dedicated pin called EAREF (see the related section) that allows providing an
external reference to the non-inverting input of the error-amplifier.
In these applications the duty cycle depends on the MOTOR's speed and sometimes 100 %
has to be set in order to go at the maximum speed. Unfortunately in these conditions the
bootstrap capacitor can not be recharged and the system cannot work properly. Some PWM
controller limits the maximum duty-cycle to 80-90 % in order to keep the bootstrap cap
charged but this make worse the performance during the load transient. Thanks to the
“bootstrap anti-discharging system” the L6732 can work at 100 % without any problem. The
following picture shows the device behavior when input voltage is 5 V and 100 % is set by
the external reference.
Figure 16. 100 % duty cycle operation
DS(on)
. In some cases the OCP can be
Device description
21/37