MAX1703ESE+T Datasheet MAX1703ESE+T, MAX1703ESE | P10-P12

MAX1703

Synchronized PWM Operation

The MAX1703 can be synchronized in PWM mode to a

200kHz to 400kHz frequency by applying an external

clock to CLK/SEL. This allows the user to set the har-

monics to avoid IF bands in wireless applications. The

synchronous rectifier is also active during synchronized

PWM operation.

Low-Power PFM Operation

Pulling CLK/SEL low places the MAX1703 in a low-

power mode. During low-power mode, PFM operation

regulates the output voltage by transferring a fixed

amount of energy during each cycle, and then modulat-

ing the pulse frequency to control the power delivered

to the output. The devices switch only as needed to

service the load, resulting in the highest possible effi-

ciency at light loads. Output current capability in PFM

mode is 150mA (max). The output voltage is typically

1% higher than in PWM mode.

During PFM operation, the error comparator detects the

output voltage falling out of regulation and sets a flip-

flop, which turns on the N-channel MOSFET switch

(Figure 4). When the inductor current ramps to the PFM

mode current limit (800mA typical) and stores a fixed

amount of energy, the current-sense comparator resets

a flip-flop. The flip-flop turns off the N-channel switch

and turns on the P-channel synchronous rectifier. A

second flip-flop, previously reset by the switch’s “on” sig-

nal, inhibits the error comparator from initiating another

cycle until the energy stored in the inductor is transferred

to the output filter capacitor and the synchronous rectifier

current has ramped down to 80mA. This forces operation

with a discontinuous inductor current.

Synchronous Rectifier

The MAX1703 features an internal 140mΩ, P-channel

synchronous rectifier to enhance efficiency. Synchro-

nous rectification provides a 5% efficiency improve-

ment over similar nonsynchronous boost regulators. In

PWM mode, the synchronous rectifier is turned on dur-

ing the second half of each switching cycle. In low-

power mode, an internal comparator turns on the

synchronous rectifier when the voltage at LX exceeds

the boost regulator output, and then turns it off when

the inductor current drops below 80mA.

Low-Voltage Start-Up Oscillator

The MAX1703 uses a CMOS, low-voltage start-up oscil-

lator for a 1.1V guaranteed minimum start-up input volt-

age at +25°C. On start-up, the low-voltage oscillator

switches the N-channel MOSFET until the output volt-

age reaches 2.15V. Above this level, the normal boost-

converter feedback and control circuitry take over.

Once the device is in regulation, it can operate down to

a 0.7V input, since internal power for the IC is boot-

strapped from the output via the OUT pin. Do not apply

full load until the output exceeds 2.3V (max).

1-Cell to 3-Cell, High-Power (1.5A),

Low-Noise, Step-Up DC-DC Converter

10 ______________________________________________________________________________________

2.7A TYP

CURRENT

LIMIT

OSC

REF

LXP

LXN

POUT

PGND

Figure 3. Simplified PWM Controller Block Diagram

ERROR

COMPARATOR

REF

800mA TYP

CURRENT

LIMIT

LOGIC HIGH

POUT

PGND

LXP

LXN

Figure 4. Controller Block Diagram in Low-Power PFM Mode

Shutdown

The MAX1703 shuts down to reduce quiescent current

to 1µA. During shutdown (ON = V

OUT

), the reference,

low-battery comparator, gain block, and all feedback

and control circuitry are off. The boost converter’s out-

put drops to one Schottky diode drop below the input.

Power-Good (POK) Comparator

The MAX1703 features an uncommitted POK compara-

tor. The internal POK comparator has an open-drain

output (POK) capable of sinking 1mA. When the input

(POKIN) rises above the 1.25V reference, the POK

open-drain output turns off. The POKIN input has 10mV

of hysteresis.

To provide a power-good signal, connect the POKIN

input to an external resistor-divider between OUT and

GND (Figure 5). Calculate the resistor values as follows:

R3 = R4(V

/ V

REF

- 1)

where V

is the desired input voltage trip threshold.

Since the input bias current into POKIN is less than

20nA, R4 can be a large value (such as 270kΩ or less)

without sacrificing accuracy. Connect the resistor volt-

age-divider as close to the IC as possible, within 0.2in.

(5mm) of POKIN.

Reference

The MAX1703 has an internal 1.250V, 1% bandgap ref-

erence. Connect a 0.22µF bypass capacitor to GND

within 0.2in. (5mm) of the REF pin. REF can source up

to 50µA of external load current.

Gain Block

The MAX1703 gain block can function as a second

comparator, or can be used to build a linear regulator

using an external P-channel MOSFET pass device. The

gain-block output is a single-stage transconductance

amplifier that drives an open-drain N-channel MOSFET.

The g

of the entire gain-block stage is 10mmho.

Figure 6 shows the gain block used in a linear-regulator

application. The output of an external P-channel pass

element is compared to the internal reference. The dif-

ference is amplified and used to drive the gate of the

pass element. Use a logic-level PFET, such as an

NDS336P (R

DS(ON)

= 270mΩ) from Fairchild. This con-

figuration allows ripple reduction at the output. If a

lower R

DS(ON)

PFET is used, then the linear regulator

output filter capacitance may need to be increased.

To use the gain block as a comparator, refer to the

Power-Good (POK) Comparator

section.

MAX1703

1-Cell to 3-Cell, High-Power (1.5A),

Low-Noise, Step-Up DC-DC Converter

______________________________________________________________________________________ 11

GNDPGND

POUT

OUT

LXP, LXN

MBR0520L

OUTPUT

100µF

2 x 220µF

4.7µH

POK

REF

CLK/SEL

AIN

POKIN

0.22µF

NOTE: HEAVY LINES INDICATE HIGH-CURRENT PATHS.

0.22µF

10Ω

MAX1703

SIGNAL GROUND

POWER GROUND

Figure 5. Adjustable Output (PWM Mode)

GNDPGND

POUT

OUT

LXP, LXN

100µF

MBR0520L

BOOST

OUTPUT

47µF

LINEAR

REGULATED

OUTPUT

20k

0.22µF

330µF

10Ω

0.22µF

4.7µH

POK

REF

CLK/SEL

AIN

POKIN

100k

MAX1703

SIGNAL GROUND

POWER GROUND

Figure 6. Using the Gain Block as a Linear Regulator

MAX1703

__________________Design Procedure

Setting the Output Voltages

Set the output voltage between 2.5V and 5.5V by con-

necting a resistor voltage-divider to FB from OUT to

GND, as shown in Figure 2. The resistor values are then

as follows:

R1 = R2(V

OUT

/ V

- 1)

where V

, the boost-regulator feedback setpoint, is

1.24V. Since the input bias current into FB is less than

20nA, R2 can have a large value (such as 270kΩ or

less) without sacrificing accuracy. Connect the resistor

voltage-divider as close to the IC as possible, within

0.2in. (5mm) of the FB pin.

Inductor Selection

The MAX1703’s high switching frequency allows the

use of a small surface-mount inductor. A 4.7µH induc-

tor should have a saturation-current rating that exceeds

the N-channel switch current limit. However, it is gener-

ally acceptable to bias the inductor current into satura-

tion by as much as 20%, although this will slightly

reduce efficiency. For high efficiency, choose an induc-

tor with a high-frequency core material, such as ferrite,

to reduce core losses. To minimize radiated noise, use

a toroid, pot core, or shielded bobbin inductor. See

Table 3 for suggested components and Table 4 for a

list of component suppliers. Connect the inductor from

the battery to the LX pins as close to the IC as possible.

Output Diode

Use a Schottky diode such as a 1N5817, MBR0520L, or

equivalent. The Schottky diode carries current during

both start-up and PFM mode after the synchronous recti-

fier turns off. Thus, its current rating only needs to be

500mA. Connect the diode between LXN/LXP and

POUT, as close to the IC as possible. Do not use ordi-

nary rectifier diodes, since slow switching speeds and

long reverse recovery times will compromise efficiency

and load regulation.

Input and Output Filter Capacitors

Choose input and output filter capacitors that will ser-

vice the input and output peak currents with accept-

able voltage ripple. Choose input capacitors with

working voltage ratings over the maximum input volt-

age, and output capacitors with working voltage ratings

higher than the output.

A 330µF, 100mΩ, low-ESR tantalum capacitor is recom-

mended for a 5V output. For full output load current,

one 470µF or two 220µF, 100mΩ low-ESR tantalum

capacitors are recommended for a 3.3V output. The

input filter capacitor (C

) also reduces peak currents

drawn from the input source and reduces input switch-

ing noise. The input voltage source impedance deter-

mines the required size of the input capacitor.

When operating directly from one or two NiCd cells

placed close to the MAX1703, use a 100µF, low-ESR

input filter capacitor.

Sanyo OS-CON and Panasonic SP/CB-series ceramic

capacitors offer the lowest ESR. Low-ESR tantalum

capacitors are a good choice and generally offer a

good tradeoff between price and performance. Do not

exceed the ripple current ratings of tantalum capaci-

tors. Avoid most aluminum-electrolytic capacitors,

because their ESR is often too high.

1-Cell to 3-Cell, High-Power (1.5A),

Low-Noise, Step-Up DC-DC Converter

12 ______________________________________________________________________________________

Sanyo OS-CON series

Sumida RCH654 seriesThrough Hole

Matsuo 267 series

CAPACITORS

1N5817

DIODESPRODUCTION INDUCTORS

Table 3. Component Selection Guide

Table 4. Component Suppliers

(714) 960-6492USA: (714) 969-2491Matsuo

(847) 639-1469USA: (847) 639-6400Coilcraft

(803) 626-3123

FAXSUPPLIER

USA: (803) 946-0690

(800) 282-4975

AVX

PHONE

Nichicon PL series

Sprague 595D series

(602) 994-6430USA: (602) 303-5454Motorola

(619) 661-1055

81-7-2070-1174

USA: (619) 661-6835

Japan: 81-7-2070-6306

Sanyo

(847) 956-0702

81-3-3607-5144

USA: (847) 956-0666

Japan: 81-3-3607-5111

Sumida

Sumida CDR125

AVX TPS series

Surface Mount Motorola MBR0520L

Coilcraft DO3316

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P16

MAX1703ESE+T

Mfr. #:

Buy MAX1703ESE+T

Manufacturer:

Maxim Integrated

Description:

Switching Voltage Regulators 1-3 Cell 1A Step-Up DC/DC Converters

Lifecycle:

New from this manufacturer.

Delivery:

DHL FedEx Ups TNT EMS

Payment:

T/T Paypal Visa MoneyGram Western Union

MAX1703ESE+T

MAX1703ESE+T

Products related to this Datasheet