MAX1749EUK-T 查看數據表（PDF） - Maxim Integrated

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MAX1749EUK-T

SOT23 Vibrator Motor Driver

Maxim Integrated 

SOT23 Vibrator Motor Driver

IN

OUT

CIN

BATTERY 1µF

ON

OFF

MAX1749

ON

SET

GND

OUTPUT

VOLTAGE

R1

R2

COUT VIBRATOR

1µF

Figure 2. Adjustable Output Using External Feedback

Resistors

The P-channel MOSFET requires no base drive current,

which reduces quiescent current considerably. PNP-

based regulators waste considerable amounts of base

current under large loads. The MAX1749 does not suf-

fer from these problems and consumes only 80µA of

quiescent current independent of the load (see Typical

Operating Characteristics).

Output Voltage Selection

To select the preset 1.25V output, connect OUT directly

to SET. To adjust the output (1.25V to 6.5V), use two

external resistors connected as a voltage divider to SET

(Figure 2). The output voltage is set by the following

equation:

VOUT = VSET (1 + R1 / R2)

where VSET = 1.25V. To simplify resistor selection:

R1 =

R2





VOUT

VSET



− 1

Choose R2 = 100kΩ to optimize power consumption,

accuracy, and high-frequency power-supply rejection.

The total current through the external resistive feedback

and load should not be less than 10µA.

ON/OFF

Drive ON high to provide power to the load. Drive ON

low to disable power to the load and reduce the supply

current to typically 0.1nA (1µA max). Refer to the

ON/OFF waveforms in the Typical Operating Char-

acteristics. When ON goes high, output current rises to

the current limit until VOUT reaches regulation. While in

regulation, the output current drops to a lower value

sufficient to maintain motor speed. When ON goes low,

the regulator turns off; however, inertial energy in the

motor exhibits a slow output voltage decline. The

MAX1749 is designed to withstand this condition with

no negative effects.

Current Limit

The MAX1749 includes a current limiter that monitors

and controls the pass transistor’s gate voltage, estimat-

ing the output current and limiting it to about 280mA.

For design purposes, the current limit should be con-

sidered 120mA (min) to 420mA (max). The output can

be shorted to ground for an infinite time period without

damaging the part.

Thermal-Overload Protection

Thermal-overload protection limits total power dissipa-

tion in the MAX1749. When the junction temperature

exceeds TJ = +170°C, the thermal sensor sends a sig-

nal to the ON/ OFF logic, turning off the pass transistor

and allowing the IC to cool. The thermal sensor will turn

the pass transistor on again after the IC’s junction tem-

perature cools by typically 20°C, resulting in a pulsed

output during continuous thermal-overload conditions.

Operating Region and Power Dissipation

Maximum power dissipation of the MAX1749 depends

on the thermal resistance of the case and circuit board,

the temperature difference between the die junction

and ambient air, and the rate of air flow. The power dis-

sipation across the device is P = IOUT (VIN - VOUT). The

resulting maximum power dissipation is:

PMAX = (TJ - TA) / θJA

where (TJ - TA) is the temperature difference between

the MAX1749 die junction and the surrounding air, and

θJA is +140°C/W.

GND performs the dual function of providing an electri-

cal connection to ground and channeling heat away.

Connect GND to a large pad or ground plane.

Reverse Battery Protection

The MAX1749 has a unique protection scheme that lim-

its the reverse supply current to less than 1mA when

either VIN or VON falls below ground. The circuitry moni-

tors the polarity of these two pins, disconnecting the

internal circuitry and parasitic diodes when the battery

is reversed. This feature prevents the device from over-

heating and damaging the battery.

VIN > 5.5V Minimum Load Current

When operating the MAX1749 with an input voltage

above 5.5V, the minimum current through the external

feedback resistors and load must be 30µA.

6 _______________________________________________________________________________________

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