BD3504FVM,BD3500FVM,BD3501FVM,BD3502FVM 
Technical Note
 
14/16 
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2010.05  -  Rev.A
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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 礔 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 礔 
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. 
20. We are certain that examples of applied circuit diagrams are recommendable,   
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. 
 
OUTPUT  PIN 
(Example)