BD9329AEFJ_15 Datasheet, PDF (16/23 Pages) Rohm – Synchronous Buck Converter with Integrated FET

BD9329AEFJ
Operational Notes – continued
11. Unused Input Pins
Input pins of an IC are often connected to the gate of a MOS transistor. The gate has extremely high impedance and
extremely low capacitance. If left unconnected, the electric field from the outside can easily charge it. The small charge
acquired in this way is enough to produce a significant effect on the conduction through the transistor and cause
unexpected operation of the IC. So unless otherwise specified, unused input pins should be connected to the power
supply or ground line.
12. Regarding the Input Pin of the IC
This monolithic IC contains P+ isolation and P substrate layers between adjacent elements in order to keep them
isolated. P-N junctions are formed at the intersection of the P layers with the N layers of other elements, creating a
parasitic diode or transistor. For example (refer to figure below):
When GND > Pin A and GND > Pin B, the P-N junction operates as a parasitic diode.
When GND > Pin B, the P-N junction operates as a parasitic transistor.
Parasitic diodes inevitably occur in the structure of the IC. The operation of parasitic diodes can result in mutual
interference among circuits, operational faults, or physical damage. Therefore, conditions that cause these diodes to
operate, such as applying a voltage lower than the GND voltage to an input pin (and thus to the P substrate) should be
avoided.
Figure 29. Example of monolithic IC structure
13. Thermal Shutdown Circuit(TSD)
This IC has a built-in thermal shutdown circuit that prevents heat damage to the IC. Normal operation should always be
within the IC’s power dissipation rating. If however the rating is exceeded for a continued period, the junction
temperature (Tj) will rise which will activate the TSD circuit that will turn OFF all output pins. When the Tj falls below the
TSD threshold, the circuits are automatically restored to normal operation.
Note that the TSD circuit operates in a situation that exceeds the absolute maximum ratings and therefore, under no
circumstances, should the TSD circuit be used in a set design or for any purpose other than protecting the IC from heat
damage.
14. Over Current Protection Circuit (OCP)
This IC incorporates an integrated overcurrent protection circuit that is activated when the load is shorted. This
protection circuit is effective in preventing damage due to sudden and unexpected incidents. However, the IC should
not be used in applications characterized by continuous operation or transitioning of the protection circuit.
15. EN control speed
Chattering happens if standing lowering speed is slow when standing of EN pin is lowered. The reverse current in
which the input side and the pressure operation are done from the output side is generated when chattering operates
with the output voltage remained, and there is a case to destruction. Please set to stand within 100µs when you control
ON/OFF by the EN signal.
16. About output voltage when EN terminal on
When restarting by EN terminal, BD9329AEFJ starts from 0V. When an electric charge is left in an output capacitance at
this time, electric current discharge from an output capacitance is performed. When many electric charges are left in an
output capacitance, this electrical current discharge becomes big, and BD9329AEFJ sometimes comes to destruction.
Therefore please do the discharge control to follow conditions of output voltage when EN terminal on.
In case of output capacitor value is less than 100 μF,: Please set the output voltage less than 2.0V when EN terminal on.
In case of output capacitor value is more than 100 μF,: Please set the output voltage based on the next formula.
(-0.33)
(Output voltage when EN terminal on [V]) < 9.15 x ( Output capacitance [μF] )
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TSZ22111・15・001
16/19
TSZ02201-0323AAJ00010-1-2
16.Feb.2015 Rev.003