BD3504FVM,BD3500FVM,BD3501FVM,BD3502FVM

Technical Note

9/16

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2010.05 - Rev.A

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Pin Function Descriptions

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VCC

BD3500/01/02/04FVM has an independent power input pin for an internal circuit operation of IC. This is used for bias of

IC internal circuit and external N-MOSFET.

The voltage used of VCC terminal is 5.0V and maximum current is 1.7 mA.

It is recommended to connect a bypass capacitor of 0.1 µF or so to VCC pin.

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EN

With an input of 2.0 volts or higher, the EN terminal turns to “High” level and VOUT is outputted. At 0.8V or lower, it

detects “Low” level and VOUT is turned OFF and simultaneously, the discharge circuit inside the VS terminal is activated

and lowers output voltage (150 mA (Min) when VFB//VS=1V and VEN=0V).

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VIN(BD3500/01/02FVM)

The VIN terminal is a drain voltage detection terminal of external N-MOSFET. In the event that the VIN terminal is lower

than 1.1 times the output set voltage, output is turned OFF to prevent low-input maloperation.

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VD(BD3504FVM only)

The VD terminal is a drain voltage detection terminal of external N-MOSFET. In the event that drain voltage (VIN) is low,

output voltage is turned OFF to prevent low-input maloperation. The reset voltage (VDUVLO) of drain voltage low-input

maloperation prevention circuit is determined by the following equation:

In the event that the maloperation prevention set resistance at the time of low-input drain voltage is set to a resistance

value same as output voltage set resistor (R1 = R1’, R2 = R2’), low-input maloperation prevention (UVLO) is reset when

drain voltage (VIN) reaches 70% of the output voltage. UVLO detects only at the startup of the EN terminal.

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VFB(BD3504FVM only)

The VFB terminal is a terminal to decide output voltage and is determined by the following equation:

VFB is controlled to achieve 0.65 V (typ.).

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NRCS terminal

he NRCS terminal is a constant current output terminal, and operates as



Soft-Start ... during start-up



SCP-Delay ... after start-up (BD3504FVM only).

How to set Soft-Start of NRCS terminal

The output voltage startup time (TNRCS) 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 (INRCS) of 20 µA (Typ.) output, and charges

capacitor (CNRCS) externally connected. By changing over to internal reference voltage (0.65V) when the NRCS

terminal reaches 0.65V, output voltage (VOUT) is fixed.

How to set NRCS terminal short protection Delay (BD3504FVM only)

BD3504FVM has short protection (SCP) activated when output voltage becomes VOUT x 0.35 (typ.) or lower. The

time when short protection is activated until latching takes place (TSCP) is determined by the following equation:

Tscp = CNRCS × Voscp ÷ Iscp

When short protection is activated, the NRCS terminal provides 20 µA (typ.) constant current output (lscp), and charges

the capacitor (CNRCS) externally connected. When the NRCS terminal reaches 1.3V (Voscp), latch operation is

carried out and output voltage is turned OFF.

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SCP(BD3500/01/02FVM)

BD3500/01/02FVM has short protection (SCP) activated when output becomes 70% or lower than the set voltage. The

Tscp = CNRCS × Voscp ÷ Iscp

When short protection is activated, the NRCS terminal provides 20 µA (typ.) constant current output (lscp), and charges

the capacitor (CNRCS) externally connected. When the NRCS terminal reaches 1.3V (Voscp), latch operation is carried

out and output voltage is turned OFF.

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VFB//VS (BD3500FVM/BD3501FVM/BD3502FVM//BD3504FVM)

VFB//VS terminal is a source voltage detection terminal of external N-MOSFET. VFB//VS terminal has the internal

discharge circuit activated to lower output voltage when EN becomes a Low level or various protection circuits (TSD, SCP,

UVLO) are activated.

・

G

G terminal is a gate drive terminal of external N-MOSFET. Because the output voltage range of G terminal is up to 5V

(VCC), it is necessary to use N-MOSFET whose threshold is lower than “5V-VOUT.” In addition, by incorporating a RC

snubber circuit to the G terminal, phase allowance of loop gain can be increased and the terminal can accommodate

ceramic capacitors.

VDUVLO=VFB×0.7×

R1’+R2

R1’

VOUT=VFB×

R1’+R2

R1’