MAX1709EUI+ Datasheet MAX1709EUI+, MAX1709ESE+T, MAX1709ESE | P7-P9

MAX1709

4A, Low-Noise, High-Frequency,

Step-Up DC-DC Converter

_______________________________________________________________________________________ 7

Pin Description

TSSOP NARROW SO NAME FUNCTION

1 1 ONA

On-Control Input. When ONA = high OR ONB = low, the device turns on

2–8 2, 3, 4 LX

Drain of n-Channel Power Switch. Connect pins 2, 3, and 4 together.

Connect external Schottky diode from LX to OUT.

11, 14 5, 8 GND Ground. Connect ground inputs together, then connect to PGND.

12 6 SS/LIM

Soft-Start and/or Current-Limit Input. Connect a capacitor from SS/LIM to

GND to control the rate at which the device reaches current limit (soft-start).

To reduce the current limit from the preset values, connect a resistor from

SS/LIM to GND (see Design Procedure). During shutdown, this pin is

internally pulled to GND to discharge the soft-start capacitor.

13 7 REF

1.26V Voltage Reference Output. Bypass with a 0.22µF capacitor to GND.

Maximum REF load is 50µA.

15 9 OUT

Output Voltage Sense Input. The device is powered from OUT. Bypass with

a 0.1µF to PGND with less than 5mm trace length. Connect a 2Ω series

resistor from the output filter capacitor to OUT (Figure 1).

16 10 FB

DC-DC Converter Feedback Input. Connect FB to GND for internally set

output voltage (see 3.3/5 pin description). Connect a resistor-divider from

the output to set the output voltage in the +2.5V to +5.5V range. FB

regulates to +1.25V (Figure 4).

18–23 11, 12, 13 PGND

Power Ground. Source of n-channel power MOSFET switch. Connect PGND

inputs together, then connect to GND.

26 14 3.3/5

Output Voltage Selection Pin. When FB is connected to GND, the regulator

uses internal feedback to set the output voltage. 3.3/5 = low sets output to

3.3V; 3.3/5 = high sets output to 5V. If an external divider is used at FB,

connect 3.3/5 to ground.

27 15 CLK

Clock Input for the DC-DC Converter. Connect to OUT for internal oscillator.

Optionally, drive with an external clock for external synchronization.

16 ONB

Shutdown Input. When ONB = high AND ONA = low, the device turns off

(Table 1).

9, 10, 17,

24, 25

— N.C. No Connect. Not internally connected.

—EP

Exposed Pad. Connect to large ground plane for maximum thermal

dissipation.

MAX1709

4A, Low-Noise, High-Frequency,

Step-Up DC-DC Converter

8 _______________________________________________________________________________________

Detailed Description

The MAX1709 step-up converter offers high efficiency

and high integration for high-power applications. It

operates with an input voltage as low as 0.7V and is

suitable for single- to 3-cell battery inputs as well as

2.5V or 3.3V regulated supply inputs. The output volt-

age is preset to +3.3V or +5.0V or can be adjusted with

external resistors for voltages between +2.5V to +5.5V.

The n-channel switch of the MAX1709EUI+ is rated for

10A

RMS

and can deliver loads up to 4A, depending on

input and output voltage. The n-channel switch of the

MAX1709ESE has a 6A

RMS

rating and supplies up to

2.4A output. The MAX1709ESE has a lower RMS switch

rating than the MAX1709EUI+, but has the same peak

switch current limit and so can supply 4A loads inter-

mittently. For flexibility, the current limit and soft-start

rate are independently programmable.

A 600kHz switching frequency allows for a small induc-

tor to be used. The switching frequency is also syn-

chronizable to an external clock ranging from 350kHz

to 1000kHz.

ONA,

ONB

The logic levels at ONA and ONB turn the MAX1709 on

or off. When ONA = 1 or ONB = 0, the part is on. When

ONA = 0 and ONB = 1, the part is off (Table 1). Logic-

high on control can be implemented by tying ONB high

and using ONA for shutdown. Implement inverted sin-

gle-line on/off control by grounding ONA and toggling

ONB. Implement momentary pushbutton On/Off as

described in the

Applications Information

section. Both

inputs have approximately 0.15V of hysteresis.

Switching Frequency

The MAX1709 switches at the fixed-frequency internal

oscillator rate (600kHz) or can be synchronized to an

external clock. Connect CLK to OUT for internal clock

operation. Apply a clock signal to CLK to synchronize

to an external clock. The frequency can be changed on

the fly. The MAX1709 will synchronize to a new external

clock rate in two cycles and will take approximately

40µs to revert to its internal clock frequency once the

external clock pulses stop and CLK is driven high.

Table 2 summarizes oscillator operation.

Figure 1. Standard Operating Circuit

2Ω

GND

ONA

GND

SS/LIM

REF

GND

ONB

CLK

3.3/5

PGND

OUT

KEEP TRACES

SHORT AND WIDE

0.22μF

0.1μF

C6, C7

2 x

150μF

1μH

OUT

1V TO 5V

ON-OFF

CONTROL

MAX1709

C1, C2

2 x 150μF

MAX1709

4A, Low-Noise, High-Frequency,

Step-Up DC-DC Converter

_______________________________________________________________________________________ 9

Operation

The MAX1709 switches at a constant frequency

(600kHz) and modulates the MOSFET switch pulse

width to control the power transferred per cycle and

regulate the voltage across the load. In low-noise appli-

cations, the fundamental and the harmonics generated

by the fixed switching frequency are easily filtered out.

Figure 2 shows the simplified functional diagram for the

MAX1709. Figure 3 shows the simplified PWM con-

troller functional diagram. The MAX1709 enters syn-

chronized current-mode PWM when a clock signal

(350kHz < f

CLK

< 1000kHz) is applied to CLK. For

wireless or noise-sensitive applications, this ensures

that switching harmonics are predictable and kept out-

side the IF frequency band(s). High-frequency opera-

tion permits low-magnitude output ripple voltage and

minimum inductor and filter capacitor size. Switching

losses will increase at the higher frequencies (see

Power Dissipation

Setting the Output Voltage

The MAX1709 features Dual-Mode™ operation. When

FB is connected to ground, the MAX1709 generates a

fixed output voltage of either +3.3V or +5V, depending

on the logic applied to the 3.3/5 input (Figure 1). The

output can be configured for other voltages, using two

external resistors as shown in Figure 4. To set the out-

put voltage externally, choose an R3 value that is large

enough to minimize load at the output but small enough

to minimize errors due to leakage and the time constant

to FB. A value of R3

≤ 50kΩ is required.

where V

= 1.24V.

Soft-Start/Current-Limit Adjustment

(SS/LIM)

The soft-start pin allows the soft-start time to be adjust-

ed by connecting a capacitor from SS/LIM to ground.

Select capacitor C3 (connected to SS/LIM pin) as:

C3 (in µF) = 3.2



where t

is the time (in seconds) it takes the switch

current limit to reach full value.

To improve efficiency or reduce inductor size at

reduced load currents, the current limit can be reduced

OUT

43 1=−

⎛

⎝

⎜

⎞

⎠

⎟

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ONA ONB MAX1709

00On

01Off

10On

11On

Figure 2. Simplified Functional Diagram

Table 2. Selecting Switching FrequencyTable 1. On/Off Logic Control

CLK MODE

0 Not allowed

1 PWM

External clock

(350kHz−1000kHz)

Synchronized PWM

PWM

CONTROLLER

STARTUP

OSCILLATOR

SEE

FIGURE 3.

OSC

UNDERVOLTAGE LOCKOUT

EN Q

600kHz

OSCILLATOR

REFERENCE

RDY

DUAL MODE

PGND

1.260V

2.15V

OUT

ONA

ONB

REF

CLK

3.3/5

GND

IC POWER

MAX1709

OUT

Dual Mode is a trademark of Maxim Integrated Products, Inc.

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15

MAX1709EUI+

Mfr. #:

Buy MAX1709EUI+

Manufacturer:

Maxim Integrated

Description:

Switching Voltage Regulators 4A High f Step-Up DC/DC Converter

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MAX1709EUI+

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