High-Side, n-Channel MOSFET

Switch Driver

_______________________________________________________________________________________

5

_______________Detailed Description

The MAX1614 uses an internal, monolithic charge pump

and low-dropout linear regulator to supply the required

high-side switch (Figure 1). The charge pump typically

supplies 30µA, charging 800pF of gate capacitance in

add a small capacitor between the GATE and SRC

pins. When turned off, GATE and SRC pull low and typi-

cally discharge an 800pF gate capacitance in 80µs.

The MAX1614 provides separate on/off control inputs

(ON and OFF). ON and OFF connect, respectively, to

the SET and RESET inputs of an internal flip-flop. When

ON is pulsed low (with OFF = high), the internal charge

pump turns on, and GATE is pumped to 8V above SRC,

turning on the external MOSFETs. The charge pump

maintains gate drive to the external MOSFETs until OFF

is pulsed low. When this happens, the internal charge

pump turns off, and GATE discharges to ground

through an internal switch. For slower turn-on times,

simply add a small capacitor.

__________ Applications Information

Connecting

ON/OFF to 3V or 5V Logic

ON and OFF internally connect to 2µA max pullup

current sources (Figure 1). The open-circuit voltage

for ON and OFF ranges from 7V to 10.5V (nominally

8.5V). Since the current sources are relatively weak,

connecting ON and OFF directly to logic powered from

lower voltages (e.g., 3V or 5V) poses no problem if the

gate outputs driving these pins can sink at least 2µA

while high.

Although the MAX1614 shutdown function was designed

to operate with a single pushbutton on/off switch, it can

also be driven by a single gate. Connect ON to GND

and drive OFF directly (Figure 2).

Maximum Switching Rate

The MAX1614 is not intended for fast switching appli-

cations. In fact, it is specifically designed to limit the

rate of change of the load current,

∆I/∆t. The maximum

switching rate is limited by the turn-on time, which is a

function of the charge-pump output current and the

on time as a function of external MOSFET gate capaci-

in the

Typical Operating Characteristics. Since turn-off

time is small compared to turn-on time, the maximum

Adding Gate Capacitance

The charge pump uses an internal monolithic transfer

capacitor to charge the external MOSFET gates.

Normally, the external MOSFET’s gate capacitance is

sufficient to serve as a reservoir capacitor. If the

MOSFETs are located at a significant distance from the

MAX1614, place a local bypass capacitor (100pF typ)

across the GATE and SRC pins. For slower turn-on

times, simply add a small capacitor between GATE and

SRC.

______________________________________________________________Pin Description

System Ground

GND

5

Gate-Drive Output. Connect to the gates of external, n-channel MOSFETs. When the MAX1614 is off, GATE

actively pulls to GND.

GATE

6

Source Input. Connect to the sources of external, n-channel MOSFETs. When the MAX1614 is off, SRC

actively pulls to GND.

SRC

7

Battery Input. Connect to a battery voltage between 5V and 26V.

BATT

8

between BATT, LBI, and GND to set the battery undervoltage trip threshold (see

Typical Operating Circuit).

LBI

4

LBO

3

PIN

RESET Input to the On/Off Latch. Pulse OFF low with ON high to turn off the external MOSFET switch. When

both ON and OFF are low, the part is off.

OFF

2

SET Input to the On/Off Latch. Pulse ON low with OFF high to turn on the external MOSFET switch. When

both ON and OFF are low, the part is off.

ON

1

FUNCTION

NAME