Datasheet MAX1614 (Analog Devices) - 5

MAX1614 High-Side, n-Channel MOSFET Switch Driver
Pin Description PIN NAME FUNCTION
1 ON 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. 2 OFF 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. 3 LBO Open-Drain, Low-Battery Comparator Output. LBO is low when VLBI is below the trip point. 4 LBI Low-Battery Comparator Input. LBO goes low when VLBI falls below 1.20V (typ). Connect a voltage-divider between BATT, LBI, and GND to set the battery undervoltage trip threshold (see Typical Operating Circuit). 5 GND System Ground 6 GATE Gate-Drive Output. Connect to the gates of external, n-channel MOSFETs. When the MAX1614 is off, GATE actively pulls to GND. 7 SRC Source Input. Connect to the sources of external, n-channel MOSFETs. When the MAX1614 is off, SRC actively pulls to GND. 8 BATT Battery Input. Connect to a battery voltage between 5V and 26V.
Detailed Description
3V or 5V) poses no problem if the gate outputs driving The MAX1614 uses an internal, monolithic charge pump these pins can sink at least 2μA while high. and low-dropout linear regulator to supply the required Although the MAX1614 shutdown function was designed 8V VGS voltage to fully enhance an n-channel MOSFET to operate with a single pushbutton on/off switch, it can high-side switch (Figure 1). The charge pump typically also be driven by a single gate. Connect ON to GND and supplies 30μA, charging 800pF of gate capacitance in drive OFF directly (Figure 2). 400μs (VBATT = 15V). For slower turn-on times, simply add a small capacitor between the GATE and SRC pins.
Maximum Switching Rate
When turned off, GATE and SRC pull low and typically The MAX1614 is not intended for fast switching applica- discharge an 800pF gate capacitance in 80μs. tions. In fact, it is specifically designed to limit the rate of change of the load current, ΔI/Δt. The maximum switching The MAX1614 provides separate on/off control inputs (ON rate is limited by the turn-on time, which is a function of and OFF). ON and OFF connect, respectively, to the SET the charge-pump output current and the total capacitance and RESET inputs of an internal flip-flop. When ON is on GATE (C pulsed low (with OFF = high), the internal charge pump GATE). Calculate the turn-on time as a func- tion of external MOSFET gate capacitance using the turns on, and GATE is pumped to 8V above SRC, turning Gate Charging Current vs. V on the external MOSFETs. The charge pump maintains BATT graph in the Typical Operating Characteristics. Since turn-off time is small gate drive to the external MOSFETs until OFF is pulsed low. compared to turn-on time, the maximum switching rate is When this happens, the internal charge pump turns off, and approximately 1/t GATE discharges to ground through an internal switch. For ON. slower turn-on times, simply add a small capacitor.
Adding Gate Capacitance Applications Information
The charge pump uses an internal monolithic trans- fer capacitor to charge the external MOSFET gates.
Connecting ON/OFF to 3V or 5V Logic
Normally, the external MOSFET’s gate capacitance is suf- ON and OFF internally connect to 2μA max pullup current ficient to serve as a reservoir capacitor. If the MOSFETs sources (Figure 1). The open-circuit voltage for ON and are located at a significant distance from the MAX1614, OFF ranges from 7V to 10.5V (nominally 8.5V). Since the place a local bypass capacitor (100pF typ) across the current sources are relatively weak, connecting ON and GATE and SRC pins. For slower turn-on times, simply OFF directly to logic powered from lower voltages (e.g., add a small capacitor between GATE and SRC. www.maximintegrated.com Maxim Integrated │ 5