Pin Descriptions

No.

Pin.

Descriptions

1

Boot

This pin provides ground referenced bias voltage to the upper MOSFET driver. A

bootstrap circuit is used to create a voltage suitable to drive a logic-lever N-channel

MOSFET. It can take 20V as the maximum voltage. It can be powered by a DC power

supply or powered by a boost strap circuit.

2

Ugate

This pin provides the PWM controlled gate driver for the upper MOSFET. It is also

monitored by the adaptive shoot-through protection circuitry to determine when the

upper MOSFET can be turned on. The sourcing Rds(on) is 15Ω and the sink Rds(on) is

7Ω. Ugate can handle high voltage up to maximum 20V.

3

Gnd

This pin represents the signal and power ground for the IC. Tie this pin to the ground

island/plane through the lowest impedance connection available.

4

Lgate

This pin provides the PWM controlled gate drive for the lower MOSFET. This pin is also

monitored by the adaptive shoot-through protection circuitry to determine when the

lower MOSFET can be turned on.

5

Vcc

This pin provides the bias supply for the TS3405, as well as the lower MOSFET’s gate.

Connect a well-decoupled 5V supply to this pin.

6

FB

This pin is the inverting input of the internal error amplifier. Use this pin in combination

with the COMP Pin to compensate the voltage-control feedback loop of the converter.

7

COMP

During soft start and all the time during normal converter operation, this pin represents

the output of the error amplifier. Use this pin in combination with the FB pin to

compensate the voltage control feedback loop of the converter. Pulling COMP to a level

below 0.3V enables soft start process. The whole soft start process takes about 5mS.

8

Phase

This pin is used to monitor the voltage drop across the lower MOSFET for over current

protection. The OCP threshold is –30mV. If Phases is less thean –300mV, the upper

MOSFET cannot be turned-on in the next cycle.

Block Diagram

TS3405

2-10

2003/12 rev. A