当前位置：文档库 › MAX1935ETA15中文资料

MAX1935ETA15中文资料

General Description

The MAX1935 low-dropout linear regulator operates from a 2.25V to 5.5V supply and delivers a guaranteed 500mA load current with low 175mV dropout. The high-accuracy (±1.5%) output voltage is preset at an inter-nally trimmed voltage or can be adjusted from 0.8V to 4.5V with an external resistive-divider.

An internal PMOS pass transistor allows low 210μA supply current, making this device ideal for portable equipment such as personal digital assistants (PDAs),cellular phones, cordless phones, and other equip-ment, including base stations and docking stations.Other features include an active-low, power-OK output that indicates when the output is out of regulation, a 0.02μA shutdown mode, short-circuit protection, and thermal-shutdown protection. The MAX1935 comes in a tiny 1.9W, 8-pin 3mm x 3mm thin QFN package.

Applications

Notebook Computers

Cellular and Cordless Telephones PDAs

Palmtop Computers Base Stations USB Hubs Docking Stations

Features

o Guaranteed 500mA Output Current o Output Down to 0.8V

o Low 175mV Dropout at 500mA o ±1.5% Output Voltage Accuracy

Preset at 1.5V

Adjustable from 0.8V to 4.5V o Power-OK Output

o Low 210μA Ground Current o 0.02μA Shutdown Current o Thermal-Overload Protection o Output Current Limit

o Tiny 1.9W, 8-Pin 3mm x 3mm Thin QFN Package

MAX1935

500mA, Low-Voltage Linear Regulator

in Tiny QFN

________________________________________________________________Maxim Integrated Products 1

Pin Configuration

Ordering Information

Typical Operating Circuit

19-2599; Rev 0; 10/02

Selector Guide

For pricing, delivery, and ordering information,please contact Maxim/Dallas Direct!at 1-888-629-4642, or visit Maxim’s website at https://www.wendangku.net/doc/934548510.html,.

*Contact factory for preset output voltages.

M A X 1935

500mA, Low-Voltage Linear Regulator in Tiny QFN 2

_______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(V IN = V OUT(SETPOINT)+ 500mV or V IN = 2.25V whichever is greater, SET = GND, SHDN = IN, T A = 0°C to +85°C , unless otherwise noted. Typical values are at T

= +25°C.)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability.

IN, SHDN , POK, SET to GND...................................-0.3V to +6V OUT to GND ................................................-0.3V to (V IN + 0.3V)Output Short-Circuit Duration.....................................Continuous Continuous Power Dissipation (T A = +70°C)

8-Pin Thin QFN (derate 24.4mW/°C above +70°C).......1.95W

Operating Temperature.......................................-40°C to +85°C Junction Temperature......................................................+150°C Storage Temperature Range.............................-65°C to +150°C Lead Temperature (soldering, 10s).................................+300°C

MAX1935

500mA, Low-Voltage Linear Regulator

in Tiny QFN

_______________________________________________________________________________________3

ELECTRICAL CHARACTERISTICS (continued)

(V IN = V OUT(SETPOINT)+ 500mV or V IN = 2.25V whichever is greater, SET = GND, SHDN = IN, T A = 0°C to +85°C , unless otherwise

ELECTRICAL CHARACTERISTICS

(V IN = V OUT(SETPOINT)+ 500mV or V IN = 2.25V whichever is greater, SET = GND, SHDN = IN, T A = -40°C to +85°C , unless otherwise noted. Typical values are at T A = +25°C.) (Note 2)

M A X 1935

500mA, Low-Voltage Linear Regulator in Tiny QFN 4_______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(V IN = V OUT(SETPOINT)+ 500mV or V IN = 2.25V whichever is greater, SET = GND, SHDN = IN, T A = -40°C to +85°C , unless otherwise noted. Typical values are at T A = +25°C.) (Note 2)

OUT OUT voltage limit is equal to the value for V OUT = 4V.

Note 2:Specifications to -40°C are guaranteed by design, not production tested.

Typical Operating Characteristics

(V OUT = 3.3V, V IN = V OUT + 500mV, SHDN = IN, C IN = 1μF, C OUT = 10μF, T A = +25°C, unless otherwise noted.)

1.00.5

2.01.5

3.02.53.5

1.5

2.5

3.02.0 3.5

4.0 4.5

5.0 5.5OUTPUT VOLTAGE vs. INPUT VOLTAGE

INPUT VOLTAGE (V)

O U T P U T V O L T A G E (V )

6.0

3.25

3.263.283.273.303.313.293.320200300100400500600700800

OUTPUT VOLTAGE vs. LOAD CURRENT

M A X 1935 t o c 02

LOAD CURRENT (mA)

O U T P U T V O L T A G E (V

)

3.28

3.303.293.323.313.333.34-4010-15356085

OUTPUT VOLTAGE vs. TEMPERATURE

TEMPERATURE (°C)

O U T P U T V O L T A G E (V )

010050200150250300350400

200300100400

500600700800

DROPOUT VOLTAGE vs. LOAD CURRENT

LOAD CURRENT (mA)

D R O P O U T V O L T A G

E (m V )

0.14

0.160.180.200.220.240.260.282.0

2.5

3.0

3.5

4.0

4.5

DROPOUT VOLTAGE vs. OUTPUT VOLTAGE

M A X 1935 t o c 05

OUTPUT VOLTAGE (V)

D R O P O U T V O L T A G

E (V )

0100501502002503003504004505005506002.0

3.0

4.0

5.0

6.0

GROUND-PIN CURRENT vs. INPUT VOLTAGE

INPUT VOLTAGE (V)

G R O U N D -P I N C U R R E N T (μA )

3.52.5

4.5

5.5

MAX1935

500mA, Low-Voltage Linear Regulator

in Tiny QFN

_______________________________________________________________________________________5

Typical Operating Characteristics (continued)

(V OUT = 3.3V, V IN = V OUT + 500mV, SHDN = IN, C IN = 1μF, C OUT = 10μF, T A = +25°C, unless otherwise noted.)

100

200150

3002503504004505000

200300100400500600700800

GROUND-PIN CURRENT vs. LOAD CURRENT

LOAD CURRENT (mA)

G R O U N D -P I N C U R R E N T (μA )

150

160

180

170

190

200-40

-15

GROUND-PIN CURRENT vs. TEMPERATURE

TEMPERATURE (°C)

G R O U N D -P I N C U R R E N T (μA )

-600.01

0.1

100

1000

-50-40-30-20

-100

POWER-SUPPLY REJECTION RATIO

vs. FREQUENCY

FREQUENCY (kHz)

P S R R (d B )

0.001

0.1

100

1000

OUTPUT SPECTRAL NOISE DENSITY

vs. FREQUENCY

0.010.1

FREQUENCY (kHz)

O U T P U T S P E C T R A L N O I S E D E N S I T Y (μV /H z )

10OUTPUT NOISE DC TO 1MHz

MAX1935 toc11

20ms/div

V OUT 1mV/div

OUT = 3.3V

R OUT = 66? (50mA)

0.01

200100400600800

700REGION OF STABLE C OUT ESR

vs. LOAD CURRENT

0.1

100

FREQUENCY (kHz)

R E G I O N O F C O U T E S R

300500LOAD-TRANSIENT RESPONSE

10μs/div

I OUT

200mA/div

V OUT 20mV/div

V IN = V OUT + 500mV C IN = 10μF

R OUT = 660? TO 6.6? (5mA TO 500mA)

M A X 1935

500mA, Low-Voltage Linear Regulator in Tiny QFN 6_______________________________________________________________________________________

Pin Description

Regulator Input. Supply voltage can range from 2.25V to 5.5V. Bypass with a 1μF capacitor to GND (see the Capacitor Selection and Regulation Stability Open-Drain, Active-Low Power-OK Output. POK remains low while the output voltage (V POK threshold. Connect a 100k ? pullup resistor from POK to OUT.

Active-Low Shutdown Input. A logic low at output is low. Connect SHDN to IN for normal operation.

Ground. This pin and the exposed pad also function as a heatsink. Solder both to a large pad or to the circuit-board ground plane to maximize power dissipation.

Voltage-Setting Input. Connect SET to GND for preset output. Connect an external resistive voltage-divider from OUT to SET to set the output voltage between 0.8V and 4.5V. The SET regulation voltage is 800mV.LINE-TRANSIENT RESPONSE

MAX1935 toc15

200μs/div

V IN 1V/div 6V 3V

V OUT 10mV/div

SHUTDOWN WAVEFORM

20μs/div

2V 3V 00

V OUT 1V/div R OUT = 6.6? (500mA)

V SHDN 1V/div Typical Operating Characteristics (continued)

(V OUT = 3.3V, V IN = V OUT + 500mV, SHDN = IN, C IN = 1μF, C OUT = 10μF, T A = +25°C, unless otherwise noted.)

LOAD-TRANSIENT RESPONSE

NEAR DROPOUT

10μs/div

I OUT

200mA/div

V OUT 50mV/div

V IN = V OUT + 100mV C IN = 10μF

R OUT = 660? TO

6.6? (5mA TO 500mA)POK WAVEFORM

200μs/div

V IN 2V/div V OUT 2V/div 5V 000

V POK 2V/div R OUT = 66? (50mA)

MAX1935

500mA, Low-Voltage Linear Regulator

in Tiny QFN

_______________________________________________________________________________________7

Detailed Description

The MAX1935 is a low-dropout, low-quiescent-current linear regulator. The device supplies loads up to 500mA and is available with preset output voltages. As illustrated in Figure 1, the MAX1935 includes a 0.8V ref-erence, error amplifier, P-channel pass transistor, and internal feedback voltage-divider.

The reference is connected to the error amplifier, which compares it with the feedback voltage and amplifies the difference. If the feedback voltage is lower than the reference voltage, the pass-transistor gate is pulled lower, which allows more current to pass to the output increasing the output voltage. If the feedback voltage is too high, the pass-transistor gate is pulled up, allowing less current to pass to the output.

The output voltage is fed back through either an internal resistive voltage-divider connected to OUT or an external resistor network connected to SET. The dual-mode comparator examines V SET and selects the feed-back path. If V SET is below 35mV, the internal feedback path is used, and the output is regulated to the factory-preset voltage. Additional blocks include an output current limiter, thermal sensor, and shutdown logic.

Internal P-Channel Pass Transistor

The MAX1935 features a 0.4?P-channel MOSFET pass transistor. Unlike similar designs using PNP pass transistors, P-channel MOSF ETs require no base drive,which reduces operating current. PNP-based regulators also waste considerable current in dropout when the pass transistor saturates, and use high base-drive currents under large loads. The MAX1935 does not suffer from these problems.

Output Voltage Selection

The MAX1935’s dual-mode operation allows operation in either a preset voltage mode or an adjustable mode.Connect SET to GND to select the preset output voltage. The two-digit part number suffix identifies the output voltage. For example, the MAX1935ETA33 has a preset 3.3V output voltage. The output voltage can also be adjusted by connecting a voltage-divider from OUT to SET (F igure 2). Select R2 in the 25k ?to 100k ?range. Calculate R1 with the following equation:

R1 = R2 [(V OUT / V SET ) - 1]

where V SET = 0.8V, and V OUT can range from 0.8V to 4.5V.

Shutdown

Drive SHDN low to enter shutdown. During shutdown,the output is disconnected from the input, and supply current drops to 0.02μA. When in shutdown, POK pulls

low. The capacitance and load at OUT determine the rate at which V OUT decays. SHDN can be pulled as high as 6V, regardless of the input and output voltage.

Power-OK Output

The POK output pulls low when OUT is less than 93% of the nominal regulation voltage. Once OUT exceeds 93% of the nominal voltage, POK goes high imped-ance. POK is an open-drain N-channel output. To obtain a logic voltage output, connect a pullup resistor from POK to OUT. A 100k ?resistor works well for most applications. POK can be used to signal a microcon-troller (μC), or drive an external LED to indicate power failure. When the MAX1935 is shutdown, POK is held low independent of the output voltage. If unused, leave POK grounded or unconnected.

Current Limit

The MAX1935 monitors and controls the pass transis-tor ’s gate voltage, limiting the output current to 1.4A (typ). The output can be shorted to ground for an indefi-nite period of time without damaging the part.

Thermal-Overload Protection

Thermal-overload protection limits total power dissipa-tion in the MAX1935. When the junction temperature exceeds T J = +170°C, a thermal sensor turns off the pass transistor, allowing the device to cool. The thermal sensor turns the pass transistor on again after the junc-tion temperature cools by +20°C, resulting in a pulsed output during continuous thermal-overload conditions.Thermal-overload protection protects the MAX1935 in the event of fault conditions. For continuous operation,do not exceed the absolute maximum junction-temper-ature rating of T J = +150°C.

Operating Region and Power Dissipation

The MAX1935’s maximum power dissipation depends on the thermal resistance of the IC package and circuit board, the temperature difference between the die junction and ambient air, and the rate of air flow. The power dissipated in the device is P = I OUT ?(V IN -V OUT ). The maximum allowed power dissipation is 1.95W or:

PMAX = (T J(MAX)- T A ) / (θJC + θCA )

where T J - T A is the temperature difference between the MAX1935 die junction and the surrounding air, θJC is the thermal resistance from the junction to the case, and θCA is the thermal resistance from the case through the PC board, copper traces, and other materials to the sur-rounding air. The MAX1935 package features an exposed thermal pad on its underside. This pad lowers the package ’s thermal resistance by providing

M A X 1935

500mA, Low-Voltage Linear Regulator in Tiny QFN 8

_______________________________________________________________________________________

a direct heat conduction path from the die to the PC board. Connect the exposed backside pad and GND to the system ground using a large pad or ground plane,or multiple vias to the ground plane layer.

The MAX1935 delivers up to 0.5A(RMS) and operates with input voltages up to 5.5V, but not simultaneously.High output currents can only be sustained when input-output differential is within the limits outlined.

Applications Information

Capacitor Selection and Regulator

Stability

Connect a 1μF capacitor between IN and ground and a 10μF low equivalent series-resistance (ESR) capacitor between OUT and ground. The input capacitor (C IN )lowers the source impedance of the input supply.Reduce noise and improve load-transient response,stability, and power-supply rejection by using larger

output capacitors. The output capacitor ’s (C OUT ) ESR affects stability and output noise. Use output capacitors with an ESR of 0.1?or less to ensure stability and opti-mum transient response. Surface-mount ceramic capacitors have very low ESR and are commonly avail-able in values up to 10μF. Connect C IN and C OUT as close to the MAX1935 as possible.

Noise, PSRR, and Transient Response

The MAX1935 is designed to operate with low dropout voltages and low quiescent currents, while still maintaining good noise, transient response, and AC rejection. See the Typical Operating Characteristics for a plot of Power-Supply Rejection Ratio (PSRR) vs.F requency. When operating from noisy sources,improved supply-noise rejection and transient response can be achieved by increasing the values of the input and output bypass capacitors and through passive-filtering techniques. The MAX1935 load-transient

Figure 1. Functional Diagram

MAX1935

500mA, Low-Voltage Linear Regulator

in Tiny QFN

_______________________________________________________________________________________9

response graphs (see the Typical Operating Characteristics ) show two components of the output response: a DC shift from the output impedance due to the load current change, and the transient response. A typical transient overshoot for a step change in the load current from 5mA to 500mA is 40mV. Increasing the output capacitor ’s value and decreasing the ESR attenuates the overshoot.

Input-Output (Dropout) Voltage

A regulator ’s minimum input-to-output voltage differential (dropout voltage) determines the lowest usable supply voltage. In battery-powered systems, this determines the useful end-of-life battery voltage. Because the MAX1806uses a P-channel MOSF ET pass transistor, its dropout voltage is a function of drain-to-source on-resistance (R DS(ON)) multiplied by the load current (see the Typical Operating Characteristics ):

V DROPOUT = V IN - V OUT = R DS(ON)?I OUT

Chip Information

TRANSISTOR COUNT: 949

Figure 2. Adjustable Output Using External Feedback Resistors

Figure 3. Power Operating Regions: Maximum Output Current vs. Input-Output Voltage Difference

M A X 1935

500mA, Low-Voltage Linear Regulator in Tiny QFN

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

10____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600?2002 Maxim Integrated Products

Printed USA

is a registered trademark of Maxim Integrated Products.

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,go to https://www.wendangku.net/doc/934548510.html,/packages .)