Technical Note
7/14
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2010.05 - Rev.
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BD3506F,BD3506EFV
●Block Function
AMP
An error amplifier that compares reference voltage (VREF) to Vo and drives Nch FET (Ron = 120/100 m) of output. The
frequency characteristics are optimized so that low ESR functional polymer capacitor can be used for the output capacitor
and high-speed transient response can be achieved. The input voltage range at the AMP section is GND-2.5V and the
output voltage range of the AMP section is GND-VCC. At the time of EN OFF or UVLO, the output is brought to the LOW
level and the output NchFET is turned OFF.
EN
By the logic input pin, regulator ON/OFF is controlled. At the time of OFF, the circuit current is controlled to be 0 µA to
reduce the standby current consumption of the apparatus. In addition, EN turns ON FET that can discharge NRCS
terminal Vo and removes excess electric charge to prevent maloperation of IC on the load side. Since there is no
electrical connection with the Vcc terminal as is the case of Di for electrostatic measures, it does not depend on the input
sequence.
UVLO
UVLO turned OFF output to prevent output voltage from making maloperation at the time of Vcc reduced voltage. Same
as EN, UVLO discharges NRCS Vo. When voltage exceeds the threshold voltage (TYP 4.15V), UVLO starts output.
CURRENT LIMIT
In the event the output current that exceeds the current (2.5A or more) set inside the IC flows when output is turned ON,
output voltage is attenuated to protect the IC on the load side. When current reduces, output voltage returns to the set
voltage.
NRCS
Connecting an external capacitor to the counter-GND of NRCS pin can achieve soft start. The output voltage startup time
is determined by the time when the NRCS terminal reaches VFB (0.65V). During start-up, the NRCS terminal serves as
a constant current source of 20 µA (Typ.) output, and charges the capacitor externally connected.
TSD (Thermal Shut down)
In order to prevent thermal breakdown and thermal runaway of the IC, the output is turned OFF when chip temperature
becomes high. In addition, when temperature returns to the specified temperature, the output is recovered. However,
since the temperature protection circuit is originally built in to protect the IC itself, thermal design within Tj(max) is
requested.
VIN
This is a large-current supply line. The VIN terminal is connected to the rain of output NchFET. Since there is no
electrical connection with the Vcc terminal as is the case of Di for electrostatic measures, it does not depend on the input
sequence. However, because there is body Di of output NchFET between VIN and Vo, there is electrical connection
(Di-connection) between VIN and Vo. Consequently, when the output is turned ON/OFF by VIN, reverse current flows
from Vo to VIN, to which care must be taken.
