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Datasheet

Datasheet

BM6202FS

TSZ02201-0828AB400090-1-2

© 2013 ROHM Co., Ltd. All rights reserved.

22.FEB.2013 Rev.001

http://www.rohm.com

TSZ22111 · 15 · 001

3) Bootstrap operation

Figure 5. Charging period

Figure 6. Discharging period

The bootstrap is operated by the charge period and the discharge period being alternately repeated for bootstrap

capacitor (CB) as shown in the figure above. In a word, this operation is repeated while the output of an external

transistor is switching with synchronous rectification. Because the supply voltage of the floating driver is charged from the

VCC power supply to CB through prevention of backflow diode DX, it is approximately (VCC-1V).

The resistance series connection with DX has the impedance of approximately 200

Ω.

The capacitance value for the bootstrap is the following formula:

Example:

Output MOSFET total gate charge Qg : 25nC(max.)

The allowed drop voltage actually becomes smaller by the range of the used power supply voltage, the output MOSFET

ON resistance, the forward voltages of the internal boot diode (the drop voltage to the capacitor by the charge current),

and the power supply voltage monitor circuits etc. Please set the calculation value to the criterion about the capacitance

value tenfold or more to secure the margin in consideration of temperature characteristics and the value change, etc.

Moreover, the example of the mentioned above assumes the synchronous rectification switching. Because the total gate

charge is needed only by the carrier frequency in the upper switching section, for example 150° commutation driving, it

becomes a great capacity shortage in the above settings. Please set it after confirming actual application operation.

4) Thermal shutdown (TSD) circuit

The TSD circuit operates when the junction temperature of the gate driver exceeds the preset temperature (150°C

nominal). At this time, the controller forces all driver outputs low. Since thermal hysteresis is provided in the TSD circuit,

the chip returns to normal operation when the junction temperature falls below the preset temperature (125°C nominal).

The TSD circuit is designed only to shut the IC off to prevent thermal runaway. It is not designed to protect the IC or

guarantee its operation in the presence of extreme heat. Do not continue using the IC after the TSD circuit is activated,

and do not use the IC in an environment where activation of the circuit is assumed. Moreover, it is not possible to follow

the output MOSFET junction temperature rising rapidly because it is a gate driver chip that monitors the temperature and

it is likely not to function effectively.

5) Overcurrent protection (OCP) circuit

The overcurrent protection circuit can be activated by connecting a low value resistor for current detection between the

PGND pin and the GND pin. When the PGND pin voltage reaches or surpasses the threshold value (0.9V typical), the

gate driver outputs low to the gate of all output MOSFETs, thus initiating the overcurrent protection operation.

HO

VS

VDC

VB

L

H

DX

LO

OFF

ON

VCC

HO

VS

VDC

VB

H

L

DX

LO

ON

OFF

VCC