MAXIM MAX1776 Technical data

General Description

The MAX1776 high-efficiency step-down converter pro­vides an adjustable output voltage from 1.25V to VINfrom
supply voltages as high as 24V. An internal current-limit­ed 0.4Ω MOSFET delivers load currents up to 600mA.
Operation to 100% duty cycle minimizes dropout volt­age (240mV at 600mA).

The MAX1776 has a low 15µA quiescent current to
improve light-load efficiency and conserve battery life.
The device draws only 3µA while in shutdown.

High switching frequencies (up to 200kHz) allow the
use of tiny surface-mount inductors and output capaci­tors. The MAX1776 is available in an 8-pin µMAX pack­age, which uses half the space of an 8-pin SO. For
increased output drive capability, use the MAX1626/
MAX1627 step-down controllers, which drive an exter­nal P-channel MOSFET to deliver up to 20W.

Applications

Notebook Computers

Distributed Power Systems

Keep-Alive Supplies

Hand-Held Devices

Features

♦ Fixed 5V or Adjustable Output

♦ 4.5V to 24V Input Voltage Range

♦ Up to 600mA Output Current
♦ Internal 0.4Ω P-Channel MOSFET

♦ Efficiency Over 95%

♦ 15µA Quiescent Supply Current

♦ 3µA Shutdown Current

♦ 100% Maximum Duty Cycle for Low Dropout

♦ Current-Limited Architecture

♦ Thermal Shutdown

♦ Small 8-µMAX Package

MAX1776

24V, 600mA Internal Switch, 100% Duty Cycle,

Step-Down Converter

________________________________________________________________ Maxim Integrated Products 1

Pin Configuration

Ordering Information

SHDN

V

OUT

V

IN

ILIM LX

OUT

IN

ILIM2

GNDFB

MAX1776

µMAX

Typical Operating Circuit

19-1975; Rev 2; 7/03

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

PART TEMP RANGE PIN-PACKAGE

MAX1776EUA -40°C to +85°C 8 µMAX

8

OUT

7

MAX1776EUA

µMAX

SHDN

6

ILIM2

5

INLX

TOP VIEW

1

FB

2

GND

3

ILIM

4

MAX1776

24V, 600mA Internal Switch, 100% Duty Cycle,
Step-Down Converter

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, VIN= +12V, SHDN = IN, TA= 0°C to +85°C, unless otherwise noted.)

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, ILIM, ILIM2 to GND .................................-0.3V to 25V

LX to GND.......................................................-2V to (V

IN

+ 0.3V)

OUT, FB to GND .........................................................-0.3V to 6V

Peak Input Current .................................................................. 2A

Maximum DC Input Current.............................................. 500mA

Continuous Power Dissipation (T

A

= +70°C)

8-Pin µMAX (derate 4.1mW/°C above +70°C) .............330mW

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

)

)

)

)

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

Input Voltage Range V

Input Supply Current I

Input Supply Current in Dropout I
Input Shutdown Current SHDN = GND 3 7 µA

Input Undervoltage Lockout
Threshold

Output Voltage (Preset Mode) V

Feedback Set Voltage
(Adjustable Mode)

OUT Bias Current V

OUT Pin Maximum Voltage 5.5 V

FB Bias Current I

FB Dual Mode™ Threshold Low 50 100 150 mV

LX Switch Minimum Off-Time t

LX Switch Maximum On-Time t

LX Switch On-Resistance R

LX Current Limit I

LX Zero-Crossing Threshold -75 +75 mV

Zero-Crossing Timeout LX does not rise above the threshold 30 µs

LX Switch Leakage Current

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

IN

IN

IN(DROP

V

UVLO

OUT

V

FB

FB

OFF(MIN

ON(MAX

LX(PEAK

No load 15 28 µA

No load 50 70 µA

VIN rising 3.6 4.0 4.4

VIN falling 3.5 3.9 4.3

FB = GND 4.80 5.00 5.20 V

= 5.5V 1.65 3.5 6.25 µA

OUT

VFB = 1.3V -25 +25 nA

VFB = 1.3V 8 10 12 µs

ILIM = ILIM2 = GND 1.6 3.2

VIN = 6V

LX

VIN = 4.5V

ILIM = ILIM2 = GND 120 150 180

ILIM = GND, ILIM2 = IN 240 300 360

ILIM = IN, ILIM2 = GND 480 600 720

ILIM = ILIM2 = IN 960 1200 1440

V

= 24V,

IN

LX = GND

ILIM = GND, ILIM2 = IN 0.8 1.6

ILIM = IN, ILIM2 = GND 0.4 0.8

ILIM = ILIM2 = IN 0.4 0.8

ILIM = ILIM2 = GND 1.9 3.8

ILIM = GND, ILIM2 = IN 1.0 1.9

ILIM = IN, ILIM2 = GND 0.5 0.95

ILIM = ILIM2 = IN 0.5 0.95

TA = +25°C1

= 0°C to +85°C10

T

A

4.5 24 V

1.212 1.25 1.288 V

0.22 0.42 0.62 µs

V

Ω

mA

µA

MAX1776

24V, 600mA Internal Switch, 100% Duty Cycle,

Step-Down Converter

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VIN= +12V, SHDN = IN, TA= 0°C to +85°C, unless otherwise noted.)

ELECTRICAL CHARACTERISTICS

(Circuit of Figure 1, VIN= +12V, SHDN = IN, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)

)

)

)

)

Dropout Voltage V

Line Regulation VIN = 8V/24V, 200Ω load 0.1 %/V

Load Regulation No load/full load 0.9 %

Digital Input Level SHDN, ILIM2

Digital Input Leakage Current V

ILIM Input Level

Thermal Shutdown 10°C hysteresis 160 °C

PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS

I

DROPOUT

= 525mA, ILIM = ILIM2 = IN 0.2 V

OUT

Low 0.8

High 2.4

, V

, V

SHDN

ILIM

Low 0.05

High 2.2

= 0 or 24V, VIN = 24V -1 +1 µA

ILIM2

Input Voltage Range V

Input Supply Current I

Input Supply Current in Dropout I
Input Shutdown Current SHDN = GND 7 µA

Input Undervoltage Lockout
Threshold

Output Voltage (Preset Mode) V

Feedback Set Voltage
(Adjustable Mode)

OUT Bias Current V

OUT Pin Maximum Voltage 5.5 V

FB Bias Current I

FB Dual Mode Threshold Low 45 155 mV

LX Switch Minimum Off-Time t

LX Switch Maximum On-Time t

LX Switch On-Resistance R

LX Current Limit I

PARAMETER SYMBOL CONDITIONS MIN MAX UNITS

IN

IN

IN(DROP

V

UVLO

OUT

V

FB

FB

OFF(MIN

ON(MAX

LX

LX(PEAK

No load 28 µA

No load 70 µA

VIN rising 3.6 4.4

VIN falling 3.5 4.3

FB = GND 4.75 5.25 V

= 5.5V 1.65 6.25 µA

OUT

VFB = 1.3V -25 +25 nA

VFB = 1.3V 7.5 12.5 µs

ILIM = ILIM2 = GND 3.2

VIN = 6V

VIN = 4.5V

ILIM = ILIM2 = GND 100 200

ILIM = GND, ILIM2 = IN 200 400

ILIM = IN, ILIM2 = GND 400 800

ILIM = ILIM2 = IN 800 1600

ILIM = GND, ILIM2 = IN 1.6

ILIM = IN, ILIM2 = GND 0.8

ILIM = ILIM2 = IN 0.8

ILIM = ILIM2 = GND 3.8

ILIM = GND, ILIM2 = IN 1.9

ILIM = IN, ILIM2 = GND 0.95

ILIM = ILIM2 = IN 0.95

4.5 24 V

1.2 1.3 V

0.22 0.64 µs

V

V

V

Ω

mA

1.0

-0.7

-0.8

-0.9

-0.6

-0.5

-0.4

-0.3

-0.2

-0.1

0

00.20.1 0.3 0.4 0.5 0.6

LOAD REGULATION, CIRCUIT 5

MAX1776 toc04

I

LOAD

(A)

V

OUTPUT

(% FROM V

OUT(NOM)

)

VIN = 24V

VIN = 12V

VIN = 15V

-3

0

-1

-2

1

2

3

513117 9 15 17 19 21 23 25

V

OUTPUT

vs. VIN,

CIRCUIT 5, V

OUTPUT

= 5V

MAX1776 toc05

VIN (V)

V

OUTPUT

(%)

I

LOAD

= 1mA

I

LOAD

= 50mA

I

LOAD

= 500mA

-1.0

0.5

0

-0.5

1.0

1.5

2.0

513117 9 15 17 19 21 23 25

V

OUTPUT

vs. VIN,

CIRCUIT 5, V

OUTPUT

= 3.3V

MAX1776 toc06

VIN (V)

V

OUTPUT

(%)

I

LOAD

= 1mA

I

LOAD

= 10mA

I

LOAD

= 50mA

-1.2

-0.8

-1.0

-0.4

-0.6

0

-0.2

0.2

0 200 300100 400 500 600 700

LOAD REGULATION,

CIRCUIT 1, V

OUTPUT

= 5V

MAX1776 toc01

I

LOAD

(mA)

V

OUTPUT

(%)

VIN = 24V

VIN = 12V

VIN = 15V

-1.0

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

0200100 300 400 500 600

LOAD REGULATION,

CIRCUIT 1, V

OUTPUT

= 3.3V

MAX1776 toc02

I

LOAD

(mA)

V

OUTPUT

(%)

VIN = 24V

VIN = 12V

VIN = 15V

VIN = 5V

-1.2

-1.0

-0.6

-0.8

-0.2

0

-0.4

0.2

0 100 15050 200 250 300 350 400

LOAD REGULATION, CIRCUIT 2

MAX1776 toc03

I

LOAD

(mA)

V

OUTPUT

(%)

VIN = 24V

VIN = 12V

VIN = 15V

Typical Operating Characteristics

(Circuit of Figure 1, components from Table 3, VIN= +12V, SHDN = IN, TA= +25°C.)

MAX1776

24V, 600mA Internal Switch, 100% Duty Cycle,
Step-Down Converter

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(Circuit of Figure 1, VIN= +12V, SHDN = IN, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)

Note 1: Specifications to -40°C are guaranteed by design, not production tested.

LX Zero-Crossing Threshold -75 75 mV

LX Switch Leakage Current VIN = 24V, LX = GND 10 µA

Digital Input Level SHDN, ILIM2

Digital Input Leakage Current V

ILIM Input Level

PARAMETER SYMBOL CONDITIONS MIN MAX UNITS

Low 0.8

High 2.4

, V

, V

SHDN

ILIM

= 0 or 24V, VIN = 24V -1 1 µA

ILIM2

Low 0.05

High 2.2

V

V

MAX1776

24V, 600mA Internal Switch, 100% Duty Cycle,

Step-Down Converter

_______________________________________________________________________________________ 5

Typical Operating Characteristics (continued)

(Circuit of Figure 1, components from Table 3, VIN= +12V, SHDN = IN, TA= +25°C.)

V

vs. VIN,

OUTPUT

CIRCUIT 1, V

0.4

0.2

0

(%)

-0.2

OUTPUT

-0.4

V

-0.6

-0.8

1.0
513117 9 15 17 19 21 23 25

I

I

LOAD

LOAD

= 10mA

= 50mA

VIN (V)

EFFICIENCY vs. I

V

100

95

90

85

80

75

70

EFFICIENCY (%)

65

60

55

50

0.10 1 10 100 1000

OUTPUT

VIN = 15V

I

LOAD

OUTPUT

, CIRCUIT 5,

LOAD

= 3.3V

VIN = 6V

VIN = 12V

(mA)

= 5V

I

I

LOAD

VIN = 24V

SWITCHING FREQUENCY vs.

LOAD CURRENT, CIRCUIT 1

200

180

160

140

120

100

80

FREQUENCY (kHz)

60

40

20

0

0 200 300 400100 500 600 700 800 900

VIN = 15V

VIN = 12V

I

LOAD

VIN = 24V

(mA)

LOAD

= 500mA

= 1mA

MAX1776 toc07

MAX1776 toc10

MAX1776 toc13

0.6

0.4

0.2

0

(%)

-0.2

-0.4

OUTPUT

V

-0.6

-0.8

-1.0

-1.2
513117 9 15 17 19 21 23 25

100

95

90

85

80

75

70

EFFICIENCY (%)

65

60

55

50

0.10 1 10 100 1000

140

120

100

80

60

FREQUENCY (kHz)

40

20

0

5 10152025

V

vs. VIN,

OUTPUT

CIRCUIT 1, V

I

LOAD

I

LOAD

EFFICIENCY vs. I

= 10mA

= 50mA

V

OUTPUT

OUTPUT

VIN (V)

VIN = 24V

I

LOAD

I

LOAD

, CIRCUIT 1,

LOAD

= 3.3V

VIN = 6V

(mA)

SWITCHING FREQUENCY vs.

,

CIRCUIT 1

V

IN

I

= 500mA

LOAD

I

= 375mA

LOAD

I

= 250mA

LOAD

I

= 10mA

= 50mA

LOAD

VIN (V)

I

LOAD

= 3.3V

I

LOAD

= 500mA

VIN = 12V

I

LOAD

= 1mA

= 5mA

MAX1776 toc08

MAX1776 toc11

MAX1776 toc14

EFFICIENCY vs. I

V

100

95

90

85

80

75

70

EFFICIENCY (%)

65

60

55

50

0.10 1 10 100 1000

VIN = 6V

VIN = 15V

EFFICIENCY vs. VIN, I

100

95

CIRCUIT 5, 5V

90

85

80

CIRCUIT 1, 3.3V

75

70

EFFICIENCY (%)

65

60

55

50

7 9 10 118 1213141516

V

ACCURACY vs. TEMPERATURE

OUTPUT

1.5

1.0

0.5

0

ACCURACY (%)

OUT

-0.5

V

-1.0

-1.5

-40 20 40-20 0 60 80 100

TEMPERATURE (°C)

I

OUT

LOAD

VIN = 12V

VIN (V)

, CIRCUIT 1,

LOAD

= 5V

VIN = 24V

(mA)

LOAD

CIRCUIT 1, 5V

CIRCUIT 5, 3.3V

MAX1776 toc09

= 500mA

MAX1776 toc12

MAX1776 toc15

MAX1776

24V, 600mA Internal Switch, 100% Duty Cycle,
Step-Down Converter

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(Circuit of Figure 1, components from Table 3, VIN= +12V, SHDN = IN, TA= +25°C.)

15.0

16.0

15.5

17.0

16.5

17.5

18.0

-40 -20 0 20 40 60 80

QUIESCENT SUPPLY CURRENT

vs. TEMPERATURE

MAX1776 toc16

TEMPERATURE (°C)

QUIESCENT SUPPLY CURRENT (µA)

13.70

13.80

13.75

13.90

13.85

14.00

13.95

14.05

14.15

14.10

14.20

5 9 11 1371517192321 25

QUIESCENT SUPPLY CURRENT

vs. SUPPLY VOLTAGE

MAX1776 toc17

SUPPLY VOLTAGE (V)

QUIESCENT SUPPLY CURRENT (µA)

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 5 10 15 20 25

PEAK SWITCH CURRENT

vs. INPUT VOLTAGE, CIRCUIT 3, 0.3A

MAX1776 toc18

VIN (V)

PEAK SWITCH CURRENT (A)

L = 10µH

L = 22µH

L = 47µH

L = 100µH

LOAD-TRANSIENT RESPONSE,

CIRCUIT 5

MAX1776 toc19

I

LOAD

V

OUT

V

LX

0

1A

0

10V

10µs/div

10mA

500mA

I

L

AC COUPLED
50mV/div

LINE-TRANSIENT RESPONSE,

CIRCUIT 5, I

LOAD

= 500mA

MAX1776 toc20

V

IN

V

OUT

V

LX

AC-COUPLED
200mv/div

5V

10V

200µs/div

0

5V

LINE-TRANSIENT RESPONSE,

CIRCUIT 5, I

LOAD

= 50mA

MAX1776 toc21

V

IN

V

OUT

V

LX

15V

10V

10V

200µs/div

0

5V

AC-COUPLED
200mv/div

MAX1776

24V, 600mA Internal Switch, 100% Duty Cycle,

Step-Down Converter

_______________________________________________________________________________________ 7

Typical Operating Characteristics (continued)

(Circuit of Figure 1, components from Table 3, VIN= +12V, SHDN = IN, TA= +25°C.)

STARTUP WAVEFORM, CIRCUIT 1,

R

LOAD

= 100Ω

MAX1776 toc23

I

L

V

OUT

5V

1A

0

2µs/div

6V

0

V

SHDN

0

2V

4V

75

0.10 100010 1001

EFFICIENCY vs. I

LOAD

, CIRCUIT 3, VIN = 12V

100

85

80

95

90

MAX1776 toc24

I

LOAD

(mA)

EFFICIENCY (%)

L = 22µH

L = 47µH

L = 100µH

75

0.10 100010 1001

EFFICIENCY vs. I

LOAD

, CIRCUIT 3, VIN = 12V

100

85

80

95

90

MAX1776 toc25

I

LOAD

(mA)

EFFICIENCY (%)

L = 22µH, 0.6A

L = 10µH, 1.2A

L = 47µH, 0.3A

LX WAVEFORM, CIRCUIT 1

= 15V, I

V

IN

I

L

V

LX

V

OUT

LOAD

2µs/div

= 500mA

MAX1776 toc22

1A

0

10V

0

50mV/div

MAX1776

24V, 600mA Internal Switch, 100% Duty Cycle,
Step-Down Converter

8 _______________________________________________________________________________________

Detailed Description

The MAX1776 step-down converter is designed primar­ily for battery-powered devices and notebook comput­ers. The unique current-limited control scheme
provides high efficiency over a wide load range.
Operation up to 100% duty cycle allows the lowest pos­sible dropout voltage, increasing the usable supply
voltage range. Under no load, the MAX1776 draws only
15µA, and in shutdown mode, it draws only 3µA to fur­ther reduce power consumption and extend battery life.
Additionally, an internal 24V switching MOSFET, inter­nal current sensing, and a high switching frequency
minimize PC board space and component costs.

Current-Limited Control Architecture

The MAX1776 uses a proprietary current-limited control
scheme with operation to 100% duty cycle. This DC-DC
converter pulses as needed to maintain regulation,
resulting in a variable switching frequency that increas­es with the load. This eliminates the high supply cur­rents associated with conventional constant-frequency
pulse-width-modulation (PWM) controllers that switch
the MOSFET unnecessarily.

When the output voltage is too low, the error comparator
sets a flip-flop, which turns on the internal P-channel
MOSFET and begins a switching cycle (Figure 2). As
shown in Figure 3, the inductor current ramps up linear­ly, storing energy in a magnetic field while charging the
output capacitor and servicing the load. The MOSFET
turns off when the peak current limit is reached, or when
the maximum on-time of 10µs is exceeded and the out­put voltage is in regulation. If the output is out of regula­tion and the peak current is never obtained, the
MOSFET remains on, allowing a duty cycle up to 100%.
This feature ensures the lowest possible dropout volt­age. Once the MOSFET turns off, the flip-flop resets, the
inductor current is pulled through D1, and the current
through the inductor ramps back down, transferring the
stored energy to the output capacitor and load. The
MOSFET remains off until the 0.42µs minimum off-time
expires, and the output voltage drops out of regulation.

Pin Description

Figure 1. Typical Application Circuit

PIN NAME FUNCTION

1FB

2 GND Ground

3 ILIM

4 LX Inductor Connection. Connect LX to external inductor and diode as shown in Figure 1.

5 IN Input Supply Voltage. Input voltage range is 4.5V to 24V.

6 ILIM2

7 SHDN

8 OUT

Dual-Mode Feedback Input. Connect to GND for the preset 5V output. Connect to a resistive divider
between OUT and GND to adjust the output voltage between 1.25V and V

Peak Current Control Input. Connect to IN or GND to set peak current limit. ILIM and ILIM2 together set
the peak current limit. See Setting Current Limit.

Peak Current Control Input 2. Connect to IN or GND. ILIM and ILIM2 together set the peak current limit.
See Setting Current Limit.

Shutdown Input. A logic low shuts down the MAX1776 and reduces the supply current to 3µA. LX is high
impedance in shutdown. Connect to IN for normal operation.

Regulated Output Voltage High-Impedance Sense Input. Internally connected to a resistive divider.
Do not connect for output voltages higher than 5.5V. Connect to GND when not used.

INPUT

4.5V TO 24V

C

IN

J1

J2

CIN: 10µF, 25V CERAMIC

SEE TABLE 3 FOR OTHER COMPONENT VALUES

IN

SHDN

MAX1776

ILIM

J3

ILIM2

J4

GND

NOTE: HIGH-CURRENT PATHS SHOWN WITH BOLD LINES.

LX

OUT

FB

L1

D1

OUTPUT

C

OUT

.

IN

5V

MAX1776

24V, 600mA Internal Switch, 100% Duty Cycle,

Step-Down Converter

_______________________________________________________________________________________ 9

Input-Output (Dropout) Voltage

A step-down converter’s minimum input-to-output volt­age differential (dropout voltage) determines the lowest
usable supply voltage. In battery-powered systems,
this limits the useful end-of-life battery voltage. To maxi­mize battery life, the MAX1776 operates with duty
cycles up to 100%, which minimizes the dropout volt­age and eliminates switching losses while in dropout.
When the supply voltage approaches the output volt­age, the P-channel MOSFET remains on continuously to
supply the load.

Dropout voltage is defined as the difference between
the input and output voltages when the input is low
enough for the output to drop out of regulation. For a
step-down converter with 100% duty cycle, dropout
depends on the MOSFET drain-to-source on-resistance
and inductor series resistance; therefore, it is propor­tional to the load current:

V

DROPOUT

= I

OUT

✕

(R

DS(ON) + RINDUCTOR

)

Figure 2. Simplified Functional Diagram

Figure 3. Discontinuous-Conduction Operation

D

C

IN

SHDN

ILIM

ILIM2

ILIM
SET

MAXIMUM

ON-TIME

DELAY

MINIIMUM
OFF-TIME

DELAY

MAX1776

RQ

S

100mV

V

SET

1.25V

OUT

FB

GND

L1

LX

D1

OUTPUT

C

OUT

LX WAVEFORM, CIRCUIT 1

= 15V, I

V

IN

I

L

V

LX

V

OUT

LOAD

2µs/div

= 500mA

1A

0

10V

0

50mV/div

MAX1776

24V, 600mA Internal Switch, 100% Duty Cycle,
Step-Down Converter

10 ______________________________________________________________________________________

Shutdown (

SSHHDDNN

)

A logic low level on SHDN shuts down the MAX1776
converter. When in shutdown, the supply current drops
to 3µA to maximize battery life, and the internal P-chan­nel MOSFET turns off to isolate the output from the input.
The output capacitance and load current determine the
rate at which the output voltage decays. A logic level
high on SHDN activates the MAX1776. Do not leave
SHDN floating. If unused, connect SHDN to IN.

Thermal-Overload Protection

Thermal-overload protection limits total power dissipa­tion in the MAX1776. When the junction temperature
exceeds T

J

= +160°C, a thermal sensor turns off the
pass transistor, allowing the IC to cool. The thermal sen­sor turns the pass transistor on again after the IC’s junc­tion temperature cools by 10°C, resulting in a pulsed
output during continuous thermal-overload conditions.

Design Information

Output Voltage Selection

The feedback input features dual-mode operation.
Connect FB to GND for the 5.0V preset output voltage.
Alternatively, adjust the output voltage by connecting a
voltage-divider from the output to GND (Figure 4).
Select a value for R2 between 10kΩ and 100kΩ.
Calculate R1 with the following equation:

where VFB= 1.25V, and V

OUTPUT

may range from

1.25V to VIN.

Setting Current Limit

The MAX1776 has an adjustable peak current limit.
Configure this peak current limit by connecting ILIM
and ILIM2 as shown in Table 1.

Choose a current limit that realistically reflects the maxi­mum load current. The maximum output current is half
of the peak current limit. Although choosing a lower
current limit allows using an inductor with a lower cur­rent rating, it requires a higher inductance (see
Inductor Selection) and does little to reduce inductor
package size.

Inductor Selection

When selecting the inductor, consider these four para­meters: inductance value, saturation rating, series
resistance, and size. The MAX1776 operates with a
wide range of inductance values. For most applica­tions, values between 10µH and 100µH work best with
the controller’s high switching frequency. Larger induc­tor values will reduce the switching frequency and
thereby improve efficiency and EMI. The trade-off for
improved efficiency is a higher output ripple and slower
transient response. On the other hand, low-value induc­tors respond faster to transients, improve output ripple,
offer smaller physical size, and minimize cost. If the
inductor value is too small, the peak inductor current
exceeds the current limit due to current-sense com­parator propagation delay, potentially exceeding the
inductor’s current rating. Calculate the minimum induc­tance value as follows:

where t

ON(MIN)

= 1µs.

The inductor’s saturation current rating must be greater
than the peak switch current limit, plus the overshoot
due to the 250ns current-sense comparator propaga­tion delay. Saturation occurs when the inductor’s mag­netic flux density reaches the maximum level the core
can support and the inductance starts to fall. Choose
an inductor with a saturation rating greater than I

PEAK

in the following equation:

I

PEAK

= I

LX(PEAK)

+ (VIN- V

OUTPUT

) ✕250ns / L

Figure 4. Adjustable Output Voltage

Table 1. Current-Limit Configuration

R1 R2





V

OUTPUT










V

FB





-=×

1










CURRENT

LIMIT (mA)

150 GND GND

300 GND IN

600 IN GND

1200 IN IN

ILIM

CONNECTED TO

CONNECTED TO

L

(MIN) =

VV

()

IN(MAX) OUTPUT ON(MIN)

-

I

LX (PEAK

× t

)

ILIM2

R1

R2

OUTPUT

1.25V TO V

IN

C

OUT

INPUT

4.5V TO 24V

C

IN

IN

SHDN

ILIM

ILIM2

GND

MAX1776

LX

L1

D1

FB

OUT

Inductor series resistance affects both efficiency and
dropout voltage (see Input-Output (Dropout) Voltage).
High series resistance limits the maximum current avail­able at lower input voltages, and increases the dropout
voltage. For optimum performance, select an inductor
with the lowest possible DC resistance that fits in the
allotted dimensions. Some recommended component
manufacturers are listed in Table 2.

Maximum Output Current

The MAX1776 converter’s output current determines
the regulator’s switching frequency. When the convert­er approaches continuous mode, the output voltage
falls out of regulation. For the typical application, the
maximum output current is approximately:

I

LOAD(MAX)

= 1/2 I

LX (PEAK)(MIN)

For low-input voltages, the maximum on-time may be
reached and the load current is limited by:

I

LOAD

= 1/2 (VIN- V

OUT

) ✕10µs / L

Output Capacitor

Choose the output capacitor to service the maximum
load current with acceptable voltage ripple. The output
ripple has two components: variations in the charge
stored in the output capacitor with each LX pulse, and
the voltage drop across the capacitor’s equivalent
series resistance (ESR) caused by the current into and
out of the capacitor:

V

RIPPLE

≅ V

RIPPLE(ESR)

+ V

RIPPLE(C)

The output voltage ripple as a consequence of the ESR
and output capacitance is:

where I

PEAK

is the peak inductor current (see Inductor
Selection). The worst-case ripple occurs at no-load.
These equations are suitable for initial capacitor selec­tion, but final values should be set by testing a proto­type or evaluation circuit. As a general rule, a smaller
amount of charge delivered in each pulse results in
less output ripple. Since the amount of charge deliv­ered in each oscillator pulse is determined by the
inductor value and input voltage, the voltage ripple
increases with larger inductance, and as the input volt­age decreases. See Table 3 for recommended capaci­tor values and Table 2 for recommended component
manufacturers.

Input Capacitor

The input filter capacitor reduces peak currents drawn
from the power source and reduces noise and voltage
ripple on the input caused by the circuit’s switching.
The input capacitor must meet the ripple-current
requirement (I

RMS

) imposed by the switching current

defined by the following equation:

For most applications, nontantalum chemistries (ceram­ic, aluminum, polymer, or OS-CON) are preferred due to
their robustness to high inrush currents typical of sys­tems with low-impedance battery inputs. Alternatively,
connect two (or more) smaller value low-ESR capacitors
in parallel to reduce cost. Choose an input capacitor
that exhibits less than +10°C temperature rise at the
RMS input current for optimal circuit longevity.

MAX1776

24V, 600mA Internal Switch, 100% Duty Cycle,

Step-Down Converter

______________________________________________________________________________________ 11

Table 2. Component Suppliers

V

RIPPLE(ESR) PEAK

V

RIPPLE(C)

ESR I

=×

LI I

×

=

C

2VVVV

-

()

PEAK OUTPUT

×

OUT OUTPUT

2






IN OUTPUT

IN

-








IV

I

LOAD OUTPUT

=×−

RMS

V

IN

4

V



3



IN

V

OUTPUT



1




SUPPLIER WEBSITE

DIODES

Central Semiconductor www.centralsemi.com

Fairchild www.fairchildsemi.com

General Semiconductor www.gensemi.com

International Rectifier www.irf.com

Nihon

On Semi www.onsemi.com

Vishay-Siliconix

Zetex

CAPACITORS

AVX www.avxcorp.com

Kemet www.kemet.com

Nichicon www.nichicon-us.com

Sanyo www.sanyo.com

Taiyo Yuden www.t-yuden.com

INDUCTORS

Coilcraft www.coilcraft.com

Coiltronics www.cooperet.com

Pulse Engineering www.pulseeng.com

Sumida USA www.sumida.com

Toko www.tokoam.com

www.niec.co.jp/engver2/
niec.co.jp_eg.htm

www.vishay.com/brands/siliconix/
main.html

www.zetex.com

MAX1776

Diode Selection

The current in the external diode (D1 in Figure 1)
changes abruptly from zero to its peak value each time
the LX switch turns off. To avoid excessive losses, the
diode must have a fast turn-on time and a low forward
voltage.

Make sure that the diode’s peak current rating exceeds
the peak current limit set by the current limit, and that
its breakdown voltage exceeds VIN. Use Schottky
diodes when possible.

MAX1776 Stability

Instability is frequently caused by excessive noise on
OUT, FB, or GND due to poor layout or improper com­ponent selection. Instability typically manifests itself as
“motorboating,” which is characterized by grouped
switching pulses with large gaps and excessive low­frequency output ripple during no-load or light-load
conditions.

PC Board Layout and Grounding

High switching frequencies and large peak currents
make PC board layout an important part of the design.
Poor layout introduces switching noise into the feed­back path, resulting in jitter, instability, or degraded
performance. High-power traces, highlighted in the

24V, 600mA Internal Switch, 100% Duty Cycle,
Step-Down Converter

12 ______________________________________________________________________________________

Table 3. Recommended Components

INPUT

CIRCUIT

1 10 to 24 600 1.20

2 10 to 24 300 0.60

3 10 to 24 150 0.30

4 10 to 24 75 0.15

5 5 to 15 600 1.20

6 5 to 15 300 0.60

7 5 to 15 150 0.30

8 5 to 15 75 0.15

VOLTAGE

(V)

MAXIMUM

LOAD

CURRENT

(mA)

I

LX(PEAK)

CURRENT

(A)

INDUCTOR CAPACITOR

10µH, 1.56A, 70mΩ
Toko D75F 646FY-100M,
10µH, 1.70A, 48mΩ
Sumida CDRH6D28-100NC,
or 10µH, 1.63A, 55mΩ
Toko D75C 646CY-100M 0.055

22µH, 1.17A, 120mΩ
Toko D75F 646FY-220M,
22µH, 1.09A, 115mΩ
Toko D75C 646CY-220M,
or 22µH, 1.20A, 95mΩ
Sumida CDRH6D28-220NC

47µH, 0.54A, 440mΩ
Sumida CDRH5D18-470

100µH, 0.29A, 766mΩ
Sumida CDRH4D28-101

5.4µH, 1.6A, 56mΩ
Sumida CDRH5D18-5R4

10µH, 1.04A, 80mΩ
Toko D73LC 817CY-100M

22µH, 0.41A, 294mΩ
Sumida CDRH4D18-220

47µH, 0.33A, 230mΩ
Coilcraft DS1608C-473

100µF, 6.3V
Sanyo POSCAP 6TPC100M

47µF, 6.3V
Sanyo POSCAP 6TPA47M

22µF, 6.3V, 1210 case
Taiyo Youden JMK325BJ226MM

10µF, 6.3V, X7R, 1206 case
Taiyo Youden JMK316BJ106ML

100µF, 6.3V
Sanyo POSCAP 6TPC100m

47µF, 6.3V
Sanyo POSCAP 6TPA47M

22µF, 6.3V, 1210 case
Taiyo Youden JMK325BJ226MM

10µF, 6.3V, X7R, 1206 case
Taiyo Youden JMK316BJ106ML

MAX1776

24V, 600mA Internal Switch, 100% Duty Cycle,

Step-Down Converter

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 13

© 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

Typical Application Circuit (Figure 1), should be as
short and wide as possible. Additionally, the current
loops formed by the power components (CIN, COUT,
L1, and D1) should be as short as possible to avoid
radiated noise. Connect the ground pins of these
power components at a common node in a star-ground
configuration. Separate the noisy traces, such as the
LX node, from the feedback network with grounded
copper. Furthermore, keep the extra copper on the

board and integrate it into a pseudo-ground plane.
When using external feedback, place the resistors as
close to the feedback pin as possible to minimize noise
coupling.

Chip Information

TRANSISTOR COUNT: 932

PROCESS: BiCMOS

Package Information

4X S

BOTTOM VIEW

0.6±0.1

0.6±0.1

8

1

TOP VIEW

ÿ 0.50±0.1

D

E H

8

1

DIM

A
A1
A2
b

c
D
e

E

H

L

α

S

INCHES

MIN

-

0.002

0.030

0.010

0.005

0.116

0.0256 BSC

0.116

0.188

0.016
0∞

0.0207 BSC

MAX

0.043

0.006

0.037

0.014

0.007

0.120

0.120

0.198

0.026
6∞

MILLIMETERS

MIN

0.05 0.15

0.25 0.36

0.13 0.18

2.95 3.05

2.95 3.05

4.78

0.41

MAX

- 1.10

0.950.75

0.65 BSC

5.03

0.66

0.5250 BSC

6∞0∞

8LUMAXD.EPS

A2

e

FRONT VIEW

A1

A

c

b

L

SIDE VIEW

α

PROPRIETARY INFORMATION

TITLE:

PACKAGE OUTLINE, 8L uMAX/uSOP

REV.DOCUMENT CONTROL NO.APPROVAL

21-0036

1

J

1