TD340ID STMicroelectronics, TD340ID Datasheet - Page 10

• Manufacturer Part Number: TD340ID
• Description: MOSFET & Power Driver ICs H-Bridge Quad MOSFET
• Manufacturer: STMicroelectronics
• Type: High Side/Low Sider

Specifications of TD340ID

• Supply Voltage (min): 6.5 V
• Supply Current: 7 mA
• Maximum Power Dissipation: 500 mW
• Maximum Operating Temperature: + 125 C
• Mounting Style: SMD/SMT
• Package / Case: SO-20
• Bridge Type: H Bridge
• Minimum Operating Temperature: - 40 C
• Number Of Drivers: 4
• Number Of Outputs: 4
• Output Current: 1.5 A
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

MOS drivers
Output drivers are designed to drive MOS with gate capacitance of up to 4 nF. A small resistor in serial
with gate input is recommended to prevent spurious oscillations due to parasitic inductance in conjunction
with gate capacitance. Typical value of these resistors are from 10 to 100 ohms, depending on the MOS
characteristics.
Charge pump
To drive the high side MOS, the TD340 has to provide a voltage of about 10V higher that the power supply
voltage. The TD340 provides an internal charge pump which acts as a voltage tripling generator clamped
to 12V and allows the output of correct gate voltage with power voltage level as low as 6.5V. Its double
balanced structure ensures low EMI Ground Noise. The internal charge pump is used to achieve correct
voltage level at startup or static states.
An 5.6k resistor needs to be connected between OSC and GND for proper operation.
Bootstrap capacitors
To achieve dynamic driving up to 25kHz, it is necessary to support the internal charge pump with
bootstrap capacitors.
Bootstrap capacitors are charged from Vbat when the lower MOS is ON. When the lower MOS is switched
off and the upper one is switched ON, the bootstrap capacitor provides the necessary current to the driver
in order to charge the gate capacitor to the right voltage level.
A design rule to select the bootstrap capacitor value is to choose ten times the gate capacitance.
For example, MOS with 4 nF gate capacitance will require bootstrap capacitors of about 47nF.
MOS gate discharge
The high side MOS are switched off with internal Gate to Source discharge (not Gate to Ground
discharge) to prevent the Gates from negative transient voltages.
Figure 4 : Typical waveforms on low and high side MOS gates.
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Upper trace : High side MOS gate
Lower trace : Low side MOS gate
TD340