BD3504FVM(2008) データシートの表示（PDF） - ROHM Semiconductor

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BD3504FVM
(Rev.:2008)

Ultra Low Dropout Linear Regulator Controllers for PC Chipsets

ROHM Semiconductor 

10.Output capacitor (C5)

Connect the output capacitor between Vo1, Vo2 terminals and GND terminal without fail in order to stabilize output voltage. The output

capacitor has a role to compensate for the phase of loop gain and to reduce output voltage fluctuation when load is rapidly changed.

When there is an insufficient capacity value, there is a possibility to cause oscillation, and when the equivalent serial resistance (ESR) of

the capacitors is large, output voltage fluctuation is increased when load is rapidly changed. About 220 μF high-performance electrolytic

capacitors are recommended, but this greatly depends on the gate capacity of external MOSFET and mutual conductance (gm),

temperature and load conditions. In addition, when only ceramic capacitors with low ESR are used, or various capacitors are connected in

series, the total phase allowance of loop gain becomes not sufficient, and oscillation may result. Thoroughgoing confirmation at

application temperature and under load range conditions is requested.

11.Input capacitor setting method (C1, C4)

The input capacitor plays a part to lower output impedance of a power supply connected to input terminals (Vcc, VIN). When output

impedance of this power supply increases, the input voltages (Vcc, VIN) become unstable and there is a possibility of giving rise to

oscillation and degraded ripple rejection characteristics. The use of capacitors of about 10 μF with low ESR, which provide less capacity

value changes caused by temperature changes, is recommended, but since input capacitor greatly depends on characteristics of the power

supply used for input, substrate wiring pattern, and MOSFET gate-drain capacity, thoroughgoing confirmation under the application

temperature, load range, and M-MOSFET conditions is requested.

12.NRCS terminal capacitor setting method (C3)

To the present IC, there mounted is a function (Non Rush Current on Start-up: NRCS) to prevent rush current from VIN to load and output

capacitor via Vo at the output voltage start-up. When the EN terminal is reset from Hi or UVLO, constant current is allowed to flow from the

NRCS terminal. By this current, voltage generated at the NRCS terminal becomes the reference voltage and output voltage is started. In

order to stabilize the NRCS set time, it is recommended to use a capacitor (B special) with less capacity value change caused by

temperature change.

13.SCP terminal capacitor setting method (C2)

The present IC incorporates a timer-latch type short-circuit protection circuit in order to prevent MOSFET from being destroyed by abnormal

current when output terminal is short-circuited (operates at the time of NRCS, too). When the output terminal voltage drops 30% from

output setting voltage, IC judges that the output is short-circuited. In such event, constant current begins to flow. When the voltage

generated in the SCP terminal reaches 1.3V (Typ) by this current, the gate terminal is brought to the Low level. In order to stabilize the

SCP setting time, a capacitor (B special) with less capacity value change caused by temperature changes is recommended. When the

SCP function is not used, short-circuit the SCP terminal to the GND terminal. In addition, when the output terminal is short-circuited, the

MOSFET gate voltage reaches the Vcc voltage and the large current that meets MOSFET characteristics flows to the output while the timer

latch type protection circuit operates. When the current capacity of VIN terminal power supply lacks, the Vin terminal voltage lowers and

the UVLO circuit operates, and the latch operation may not be finished. In such event, connect a limiting resistor across drain terminal

and VIN terminal of MOSFET.

14.Input terminals (VCC, VIN, EN)

In the present IC, N terminal, VIN terminal, and VCC terminal have an independent construction. In addition, in order to prevent

malfunction at the time of low input, the UVLO function is equipped with the VIN terminal and the VCC terminal. They begin to start output

voltage when all the terminals reach threshold voltage without depending on the input order of input terminals.

15.Maximum output current (maximum load)

The maximum output current capacity of the power supply which is composed by the use of the present IC depends on the external FET.

Consequently, confirm the characteristics of the power required for the set to be used, choose the external FET.

16.Operating ranges

If it is within the operating ranges, certain circuit functions and operations are warranted in the working ambient temperature range. With

respect to characteristic values, it is unable to warrant standard values of electric characteristics but there are no sudden variations in

characteristic values within these ranges.

17.Allowable loss Pd

With respect to the allowable loss, the thermal derating characteristics are shown in the Exhibit, which we hope would be used as a

good-rule-of-thumb. Should the IC be used in such a manner to exceed the allowable loss, reduction of current capacity due to chip

temperature rise, and other degraded properties inherent to the IC would result. You are strongly urged to use the IC within the allowable

loss.

18.The use in the strong electromagnetic field may sometimes cause malfunction, to which care must be taken.

19.In the event that load containing a large inductance component is connected to the output terminal, and generation of back-EMF at the

start-up and when output is turned OFF is assumed, it is requested to insert a protection diode.

19. In the event that load containing a large inductance component is connected to the output terminal, and generation of back-EMF at the

start-up and when output is turned OFF is assumed, it is requested to insert a protection diode.

20.We are certain that examples of applied circuit diagrams are recommendable,

(Example) OUTPUT PIN

but you are requested to thoroughly confirm the characteristics before using the IC.

In addition, when the IC is used with the external circuit changed, decide the IC with sufficient margin provided

while consideration is being given not only to static characteristics but also variations of external parts and our IC including transient

characteristics.

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