PAM2306DYP datasheet(8/12 Pages) DIODES

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PAM2306D

Document number: DS36394 Rev. 2 - 2

8 of 12

www.diodes.com

December 2014

PAM2306D

A Product Line of

Diodes Incorporated

Application Information (cont.)

For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to:

)

(





Since RDS(ON), quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete

input voltage range. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surrounding

airflow and temperature difference between junction and ambient. The maximum power dissipation can be calculated by the following formula:







)

MAX

(

Where TJ(MAX) is the maximum allowable junction temperature 125°C. TA is the ambient temperature and θJA is the thermal resistance from the

junction to the ambient. Based on the standard JEDEC for a two layers thermal test board, the thermal resistance θJA of WDFN3X3 is 60°C/W.

The maximum power dissipation at TA = +25°C can be calculated by following formula:

PD = (125°C - 25°C)/60°C/W = 1.66W

Selecting the Output Voltage

The internal reference is 0.6V (Typical). The output voltage is calculated as below:











 





The output voltage is given by Table 1.

Table 1: Resistor selection for output voltage setting.

1.2V

100k

1.5V

150k

100k

1.8V

200k

100k

2.5V

380k

120k

3.3V

540k

120k

100% Duty Cycle Operation

As the input voltage approaches the output voltage, the converter turns the P-Channel transistor continuously on. In this mode the output

voltage is equal to the input voltage minus the voltage drop across the P-Channel transistor:

VOUT = VIN - ILOAD (RDS(ON) + RL )

where RDS(ON) = P-Channel switch ON resistance, ILOAD = Output Current, RL = Inductor DC Resistance

UVLO and Soft-Start

The reference and the circuit remain reset until the VIN crosses its UVLO threshold.

The PAM2306D has an internal soft-start circuit that limits the in-rush current during start-up. This prevents possible voltage drops of the input

voltage and eliminates the output voltage overshoot. The soft-start acts as a digital circuit to increase the switch current in several steps to the

P-Channel current limit (1500mA).

Short Circuit Protection

The switch peak current is limited cycle-by-cycle to a typical value of 1500mA. In the event of an output voltage short circuit, the device

operates with a frequency of 400kHz and minimum duty cycle, therefore the average input current is typically 200mA.

Thermal Shutdown

When the die temperature exceeds 150°C, a reset occurs and the reset remains until the temperature decrease to 120°C, at which time the

circuit can be restarted.

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