Step-Up/Down DC-DC Converter

in QSOP Package

10

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__________Applications Information

Using a Single, Pushbutton On/Off Switch

A single pushbutton switch can be used to turn the

MAX1672 on and off. As shown in Figure 3, ONA is

pulled low and ONB is pulled high when the part is off.

When the momentary switch is pressed, ONB is pulled

low and the regulator turns on. The switch should be on

long enough for the µC to exit reset. The controller

issues a logic high to ONA, which guarantees the part

will stay on regardless of the switch state.

To turn off the regulator, press the switch again. The

controller reads the switch status and pulls ONA low.

When the switch is released, ONB goes high, turning

off the MAX1672.

Thermal Overload Protection

Thermal overload protection limits total power dissipa-

tion in the MAX1672. When the junction temperature

allowing the MAX1672 to cool. The pass transistor turns

on again after the IC’s junction temperature cools by

20°C, resulting in a pulsed output during thermal over-

load conditions.

Thermal overload protection is designed to protect the

MAX1672 if fault conditions occur. It is not intended to

be used as an operating mode. Prolonged operation in

thermal shutdown mode may reduce the IC’s reliability.

For continual operation, do not exceed the absolute

Power Dissipation and Operating Region

The MAX1672’s maximum power dissipation in step-

down mode depends on the thermal resistance of the

case and circuit board, the temperature difference

between the die junction and ambient air, and the air

flow rate. The power dissipated in the device is

maximum power dissipation is as follows:

the MAX1672 die junction and the surrounding air,

(or

cuit board, copper traces, and other materials to the

surrounding air. The MAX1672’s thermal resistance is

120°C/W. See the Typical Operating Characteristics for

the Maximum Output Current vs. Input Voltage Graph.

Layout Considerations

Proper PC board layout is essential to minimize noise

due to high inductor current levels and fast switching

waveforms. To maximize output power and efficiency

and minimize output ripple voltage and ground noise,

use the following guidelines when designing your

board:

• Use a ground plane.

• Keep the IC’s GND pin and the ground leads of C1

and C2 (Figure 2) less than 0.2in. (5mm) apart.

• Make all connections to the FB and LX pins as short

as possible.

• Solder the IC’s GND pin directly to the ground

plane.

Refer to the MAX1672 EV kit for a suggested PC board

layout.

MAX1672

ONA

ONB

I/O

I/O

OUT

PS

1M

Ω

1M

Ω

µC

Figure 3. Momentary Pushbutton On/Off Control