PAM2310

Document number: DS36397 Rev. 3 - 2

8 of 11

www.diodes.com

April 2020

© Diodes Incorporated

PAM2310

Application Information (continued)

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

V

I

R

I

P

IN

Q

H

)

ON

(

DS

2

O

D





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:







JA

A

)

MAX

(

J

D

T

T

P

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, t

he thermal resistance θJA of SO-8 is 90°C/W. The

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

PD = (125°C - 25°C) /90°C/W = 1.11W

Setting 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.











 



2

R

1

R

1

x

6

.

0

VO

Table 1: Resistor selection for output voltage setting.

VO

R1

R2

1.2V

150k

150k

1.5V

225k

150k

1.8V

300k

150k

2.5V

475k

150k

3.3V

680k

150k

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:





R

R

I

V

V

L

DSON

LOAD

IN

OUT







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 PAM2310 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 (3000mA).

Short Circuit Protection

The switch peak current is limited cycle-by-cycle to a typical value of 3000mA. In the event of an output voltage short circuit, the device operates

with a frequency of 500kHz and minimum duty cycle, therefore the average input current is typically 500mA.

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.