Applications Information

MOSFET Configuration

The MAX4843–MAX4846 can be used with either a sin-

gle MOSFET configuration as shown in the Typical

Operating Circuit, or can be configured with a back-to-

back MOSFET as shown in Figure 5. The back-to-back

configuration has almost zero reverse current when the

input supply is below the output.

If reverse current leakage is not a concern, a single

MOSFET can be used. This approach has half the loss of

the back-to-back configuration when used with similar

MOSFET types and is a lower cost solution. Note that if

the input is actually pulled low, the output is also pulled

low due to the parasitic body diode in the MOSFET. If

this is a concern, the back-to-back configuration should

be used.

In a typical application of the MAX4846, an external

adapter with built-in battery charger is connected to IN

and a battery is connected to the source of the external

FET. When the adapter is unplugged, IN is directly con-

nected to the battery through the external FET. Since

the battery voltage is typically greater than 3V, the

GATE voltage stays high and the device remains pow-

ered by the battery.

MOSFET Selection

The MAX4843–MAX4846 are designed for use with

either a single n-channel MOSFET or dual back-to-back

n-channel MOSFETs. In most situations, MOSFETs with

input supply is near the UVLO maximum of 3.5V, consid-

stand the full 28V IN range of the MAX4843–MAX4846.

Table 1 shows a selection of MOSFETs appropriate for

use with the MAX4843–MAX4846.

IN Bypass Considerations

For most applications, bypass IN to GND with a 1µF

ceramic capacitor. If the power source has significant

inductance due to long lead length, take care to pre-

vent overshoots due to the LC tank circuit and provide

protection if necessary to prevent exceeding the 30V

absolute maximum rating on IN.

The MAX4843–MAX4846 provide protection against

voltage faults up to 28V, but this does not include neg-

ative voltages. If negative voltages are a concern, con-

nect a Schottky diode from IN to GND to clamp

negative input voltages.

ESD Test Conditions

ESD performance depends on a number of conditions.

The MAX4843–MAX4846 are protected from ±15kV typ-

ical ESD on IN when IN is bypassed to ground with a

1µF ceramic capacitor.

Overvoltage Protection Controllers with

Low Standby Current

_______________________________________________________________________________________

7

MAX4843–

MAX4846

4

GATE

FLAG

N

3

1

IN

2

GND

INPUT

+1.2V TO +28V

1

µF

N

PART

CONFIGURATION/

PACKAGE

MANUFACTURER

Si5902DC

Dual/1206-8

30

143

Si1426DH

Single/SSOT-6

30

115

Vishay Siliconix

www.vishay.com

FDC6561AN

Dual/SSOT-6

30

145

FDC6305N

Dual/SSOT-6

20

80

FDG315N

Single/SC70-6

30

160

Fairchild Semiconductor

www.fairchildsemi.com

Figure 5. Back-to-Back External MOSFET Configuration

Table 1. MOSFET Suggestions