Rainbow Electronics MAX669 User Manual

General Description

The MAX668/MAX669 constant-frequency, pulse-width­modulating (PWM), current-mode DC-DC controllers are
designed for a wide range of DC-DC conversion applica­tions including step-up, SEPIC, flyback, and isolated­output configurations. Power levels of 20W or more can
be controlled with conversion efficiencies of over 90%.
The 1.8V to 28V input voltage range supports a wide
range of battery and AC-powered inputs. An advanced
BiCMOS design features low operating current (220µA),
adjustable operating frequency (100kHz to 500kHz),
soft-start, and a SYNC input allowing the MAX668/
MAX669 oscillator to be locked to an external clock.

DC-DC conversion efficiency is optimized with a low
100mV current-sense voltage as well as with Maxim’s
proprietary Idle Mode™ control scheme. The controller
operates in PWM mode at medium and heavy loads for
lowest noise and optimum efficiency, then pulses only as
needed (with reduced inductor current) to reduce oper­ating current and maximize efficiency under light loads.
A logic-level shutdown input is also included, reducing
supply current to 3.5µA.

The MAX669, optimized for low input voltages with a
guaranteed start-up voltage of 1.8V, requires boot­strapped operation (IC powered from boosted output). It
supports output voltages up to 28V. The MAX668 oper­ates with inputs as low as 3V and can be connected in
either a bootstrapped or non-bootstrapped (IC powered
from input supply or other source) configuration. When
not bootstrapped, it has no restriction on output voltage.
Both ICs are available in an extremely compact 10-pin
µMAX package.

Features

♦ 1.8V Minimum Start-Up Voltage (MAX669)
♦ Wide Input Voltage Range (1.8V to 28V)
♦ Tiny 10-Pin µMAX Package
♦ Current-Mode PWM and Idle Mode™ Operation
♦ Efficiency over 90%
♦ Adjustable 100kHz to 500kHz Oscillator or

SYNC Input

♦ 220µA Quiescent Current
♦ Logic-Level Shutdown
♦ Soft-Start

Applications

Cellular Telephones
Telecom Hardware
LANs and Network Systems
POS Systems

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

________________________________________________________________

Maxim Integrated Products

1

19-4778; Rev 0a; 8/98

PART
MAX668EUB
MAX669EUB

-40°C to +85°C

-40°C to +85°C

TEMP. RANGE PIN-PACKAGE

10 µMAX
10 µMAX

EVALUATION KIT MANUAL

FOLLOWS DATA SHEET

Idle Mode is a trademark of Maxim Integrated Products.

Ordering Information

Typical Operating Circuit

MAX669

FREQ

CS+

SYNC/
SHDN

PGND

FB

GND

V

CC

EXT

LDO

REF

V

OUT

= 28V

V

IN

= 1.8V to 28V

1

2

3

4

5

10

9

8

7

6

SYNC/SHDN

V

CC

EXT

PGNDREF

GND

FREQ

LDO

MAX668
MAX669

µMAX

TOP VIEW

CS+FB

Pin Configuration

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone].
For small orders, phone [phone].

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= LDO = +5V, R

OSC

= 200kΩ, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

V

CC

to GND ..........................................................-0.3V to +30V

PGND to GND....................................................................±0.3V

SYNC/

SHDN to GND.............................................-0.3V to +30V

EXT, REF to GND.....................................-0.3V to (V

LDO

+ 0.3V)

LDO, FREQ, FB, CS+ to GND ................................ -0.3V to +6V

LDO Output Current...........................................-1mA to +20mA

REF Output Current..............................................-1mA to +1mA

LDO Short Circuit to GND .........................................Momentary

REF Short Circuit to GND..........................................Continuous

Continuous Power Dissipation (T

A

= +70°C)

10-Pin µMAX (derate 5.6mW/°C above +70°C) ..........444mW

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

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

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

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

85 100 115

425 500 575

225 250 275R

OSC

= 200kΩ ±1%

Oscillator Frequency

Oscillator

1.0 1.1 1.2Rising edge, 1% hysteresisREF Undervoltage Lockout Threshold

-2 -10REF load = 0 to 50µA REF Load Regulation

1.225 1.250 1.275No load, C

REF

= 0.22µFREF Output Voltage

2.40 2.50 2.60

Sensed at LDO, falling edge,
hysteresis = 1%, MAX668 only

Undervoltage Lockout Threshold

2.65 5.50

3V ≤ VCC≤ 28V
(includes LDO dropout)

4.50 5.00 5.50

LDO Output Voltage

Reference and LDO Regulators

328MAX668

PWM Controller

Input Voltage Range, V

CC

3.5 6

SYNC/SHDN = GND, VCC= 28V

Shutdown Supply Current (VCC)

220 350VFB= 1.30V, VCC= 3V to 28VVCCSupply Current (Note 1)

0.2 1CS+ forced to GNDCS+ Input Current

51525Idle Mode Current-Sense Threshold

2.7 5.5Input Voltage Range with VCCTied to LDO

1.225 1.250 1.275FB Threshold

1 20 VFB= 1.30VFB Input Current

85 100 115Current Limit Threshold

MIN TYP MAXCONDITIONSPARAMETER

kHz

V

mV

V

V

V

µA

µA

µA

mV

mV

nA

V

V

V

UNITS

MAX669 1.8 28

LDO load =
∞ to 400Ω

5V ≤ VCC≤ 28V
(includes LDO dropout)

R

OSC

= 500kΩ ±1%

R

OSC

= 100kΩ ±1%

0.013

Typically 0.013% per mV on CS+;
VCS+ range is 0 to 100mV for 0 to full
load current.

FB Threshold Load Regulation %/mV

0.012

Typically 0.012% per % duty factor on
EXT; EXT duty factor for a step-up is:
100% (1 – VIN/V

OUT

)

FB Threshold Line Regulation %/%

REFERENCE AND LDO REGULATORS

OSCILLATOR

PWM CONTROLLER

V

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

_______________________________________________________________________________________ 3

70

100 500SYNC Input Frequency Range

SYNC/SHDN Falling Edge to Shutdown Delay

2 5 EXT high or lowEXT On-Resistance

1EXT forced to 2V

Ω

EXT Sink/Source Current

1.51.8V < V

CC

< 3.0V (MAX669)

A

SYNC/SHDN Input High Voltage

0.301.8V < V

CC

< 3.0V (MAX669)

µA

SYNC/SHDN Input Low Voltage

0.5 3.0

SYNC/SHDN = 5V

SYNC/SHDN Input Current

1.5 6.5

SYNC/SHDN = 28V

V

MIN TYP MAXCONDITIONSPARAMETER

µs

kHz

UNITS

ELECTRICAL CHARACTERISTICS (continued)

(VCC= LDO = +5V, R

OSC

= 200kΩ, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

ELECTRICAL CHARACTERISTICS

(VCC= LDO = +5V, R

OSC

= 200kΩ, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)

2.40 2.60

Sensed at LDO, falling edge,
hysteresis = 1%, MAX669 only

LDO Undervoltage Lockout Threshold

2.65 5.50

3V ≤ VCC≤ 28V
(includes LDO dropout)

4.50 5.50

5V ≤ VCC≤ 28V
(includes LDO dropout)

LDO Output Voltage

Reference and LDO Regulators

V

328MAX668

V

PWM Controller

Input Voltage Range, V

CC

6

SYNC/SHDN = GND, VCC= 28V

Shutdown Supply Current (VCC)

350VFB= 1.30V, VCC= 3V to 28V

µA

VCCSupply Current (Note 1)

1CS+ forced to GND

µA

CS+ Input Current

327

µA

Idle Mode Current-Sense Threshold

2.7 5.5

mV

Input Voltage Range with VCCTied to LDO

1.22 1.28

mV

FB Threshold

20 VFB= 1.30V nAFB Input Current

85 115

V

Current-Limit Threshold

MIN MAXCONDITIONS

V

PARAMETER

V

UNITS

86 90 94R

OSC

= 500kΩ ±1%

MAX669

LDO load =
∞ to 400Ω

1.8 28

3.0V < V

CC

< 28V

3.0V < V

CC

< 28V 2.0

0.45

V

200

Not testedSYNC Input Rise/Fall Time ns

50 200Minimum SYNC Input Low Pulse Width ns

20 45Minimum SYNC Input-Pulse Duty Cycle %

290Minimum EXT Pulse Width ns

87 90 93R

OSC

= 200kΩ ±1%

86 90 94R

OSC

= 100kΩ ±1%Maximum Duty Cycle %

PWM CONTROLLER

REFERENCE AND LDO REGULATORS

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

4 _______________________________________________________________________________________

ns

%Minimum SYNC Input-Pulse Duty Cycle 45
Minimum SYNC Input Low Pulse Width 200
SYNC Input Rise/Fall Time Not tested 200 ns

ELECTRICAL CHARACTERISTICS (continued)

(VCC= LDO = +5V, R

OSC

= 200kΩ, TA= -40°C to +85°C, unless otherwise noted.)

R

OSC

= 200kΩ ±1% 87 93

SYNC Input Frequency Range 100 500 kHz

1.8V < V

CC

< 3.0V (MAX669) 0.30

V

1.8V < V

CC

< 3.0V (MAX669) 1.5

V

SYNC/SHDN = 28V

6.5

µA

EXT On-Resistance EXT high or low 5 Ω

SYNC/SHDN Input Current

SYNC/SHDN = 5V

3.0

Note 1: This is the VCCcurrent consumed when active but not switching. Does not include gate-drive current.
Note 2: Limits at T

A

= -40°C are guaranteed by design.

222 278

UNITSPARAMETER CONDITIONS MIN MAX

R

OSC

= 200kΩ ±1%

%Maximum Duty Cycle

R

OSC

= 500kΩ ±1% 86 94

425 575R

OSC

=100kΩ ±1% kHzOscillator Frequency

85 115R

OSC

= 500kΩ ±1%

R

OSC

= 100kΩ ±1% 86 94

SYNC/SHDN Input High Voltage

3.0V < V

CC

< 28V 2.0

SYNC/SHDN Input Low Voltage

3.0V < V

CC

< 28V 0.45

VREF Output Voltage No load, C

REF

= 0.22µF 1.22 1.28

mVREF Load Regulation REF load = 0 to 50µA -10

VREF Undervoltage Lockout Threshold Rising edge, 1% hysteresis 1.0 1.2

OSCILLATOR

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

_______________________________________________________________________________________

5

50

60

65

70

75

80

85

90

95

1 10 100 1000 10,000

EFFICIENCY vs. LOAD CURRENT

(V

OUT

= 5V)

MAX668 toc01

LOAD CURRENT (mA)

EFFICIENCY (%)

55

VIN = 3.3V

VIN = 3.6V

VIN = 2V

VIN = 2.7V

BOOTSTRAPPED
FIGURE 3
R4 = 200kΩ

70

1 10,000100010 100

MAX668 EFFICIENCY vs.

LOAD CURRENT (V

OUT

= 12V)

85

75

95

80

90

MAX668 toc02

LOAD CURRENT (mA)

EFFICIENCY (%)

VIN = 5V
NON-BOOTSTRAPPED
FIGURE 4
R4 = 200kΩ

MAX668 EFFICIENCY vs.

LOAD CURRENT (V

OUT

= 24V)

MAX668 toc03

LOAD CURRENT (mA)

EFFICIENCY (%)

70

1 10,000100010 100

85

75

95

80

90

VIN = 8V

VIN = 5V

VIN = 12V

NON-BOOTSTRAPPED
FIGURE 4
R4 = 200kΩ

0

1.5

1.0

0.5

2.0

2.5

3.0

0 400300100 200 500 600 700 800 900 1000

MAX669 MINIMUM START-UP VOLTAGE

vs. LOAD CURRENT

MAX668 toc04

LOAD CURRENT (mA)

MINIMUM START-UP VOLTAGE (V)

V

OUT

= 5V

V

OUT

= 12V

BOOTSTRAPPED
FIGURE 2

0

0.5

1.5

2.0

2.5

3.0

3.5

0105 15202530

SHUTDOWN CURRENT vs.

SUPPLY VOLTAGE

MAX668 toc07

SUPPLY VOLTAGE (V)

SHUTDOWN CURRENT (µA)

1.0

CURRENT INTO VCC PIN

MAX668

MAX669

0

400

200

800

600

1000

1200

010155 202530

SUPPLY CURRENT vs.

SUPPLY VOLTAGE

MAX668 toc05

SUPPLY VOLTAGE (V)

SUPPLY CURRENT (µA)

MAX669

MAX668

CURRENT INTO VCC PIN
R

OSC

= 500kΩ

0

500

1000

2000

2500

3000

3500

4000

042681012

NO-LOAD SUPPLY CURRENT vs.

SUPPLY VOLTAGE

MAX668 toc06

SUPPLY VOLTAGE (V)

NO-LOAD SUPPLY CURRENT (µA)

1500

V

OUT

= 12V
BOOTSTRAPPED
FIGURE 2
R4 = 200kΩ

150

190

210

170

250

230

270

290

-40 -20 0 20 40 60 80 100

SUPPLY CURRENT vs.

TEMPERATURE

MAX668 toc08

TEMPERATURE (°C)

SUPPLY CURRENT (µA)

R

OSC

= 100kΩ

R

OSC

= 200kΩ

R

OSC

= 500kΩ

0.1 1 10 20

LDO DROPOUT VOLTAGE vs.

LDO CURRENT

MAX668 toc09

LDO CURRENT (mA)

LDO DROPOUT VOLTAGE (mV)

300

0

50

100

150

200

250

VIN = 3V

VIN = 4.5V

Typical Operating Characteristics

(Circuits of Figures 2, 3, 4, and 5; TA= +25°C; unless otherwise noted.)

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

6 _______________________________________________________________________________________

Typical Operating Characteristics (continued)

(Circuits of Figures 2, 3, 4, and 5; TA= +25°C; unless otherwise noted.)

1.240

1.242

1.243

1.241

1.245

1.246

1.244

1.248

1.249

1.247

1.250

-40 -20 0 20 40 60 80 100

REFERENCE VOLTAGE vs.

TEMPERATURE

MAX668 toc10

TEMPERATURE (°C)

REFERENCE VOLTAGE (V)

VCC = 5V

0

100

150

50

250

300

200

400

450

350

500

0 100 200 300 400 500

SWITCHING FREQUENCY vs. R

OSC

MAX668 toc11

R

OSC

(kΩ)

SWITCHING FREQUENCY (kHz)

VCC = 5V

0

100

300

400

500

600

-40 0-20 20 40 60 80 100

SWITCHING FREQUENCY vs.

TEMPERATURE

MAX668 toc12

TEMPERATURE (°C)

SWITCHING FREQUENCY (kHz)

200

100kΩ

165kΩ

499kΩ

VIN = 5V

100 1000 10,000

EXT RISE/FALL TIME vs.

CAPACITANCE

MAX668 toc13

CAPACITANCE (pF)

EXT RISE/FALL TIME (ns)

60

0

10

20

30

40

50

tR, VCC = 3.3V

tF, VCC = 3.3V

tR, VCC = 5V

tF, VCC = 5V

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

_______________________________________________________________________________________

7

EXITING SHUTDOWN

MAX668 toc14

OUTPUT

VOLTAGE

5V/div

INDUCTOR

CURRENT

2A/div

SHUTDOWN

VOLTAGE

5V/div

MAX668, V

IN

= 5V, V

OUT

= 12V, LOAD = 1.0A, R

OSC

= 100kΩ,

LOW VOLTAGE, NON-BOOTSTRAPPED

500µs/div

0V

0V

0A

ENTERING SHUTDOWN

MAX668 toc15

OUTPUT

VOLTAGE

5V/div

SHUTDOWN

VOLTAGE

5V/div

MAX668, V

IN

= 5V, V

OUT

= 12V, LOAD = 1.0A,

LOW VOLTAGE, NON-BOOTSTRAPPED

200µs/div

0V

0V

HEAVY-LOAD SWITCHING WAVEFORM

MAX668 toc16

V

OUT

200mV/div

AC-COUPLED

I

L

1A/div

Q1, DRAIN

5V/div

MAX668, V

IN

= 5V, V

OUT

= 12V, I

LOAD

= 1.0A,

LOW VOLTAGE, NON-BOOTSTRAPPED

1µs/div

0V

0A

LOAD-TRANSIENT RESPONSE

MAX668 toc18

OUTPUT

VOLTAGE

AC-COUPLED

100mV/div

LOAD

CURRENT

1A/div

MAX668, V

IN

= 5V, V

OUT

= 12V, I

LOAD

= 0.1A TO 1.0A,

LOW VOLTAGE, NON-BOOTSTRAPPED

1ms/div

LIGHT-LOAD SWITCHING WAVEFORM

MAX668 toc17

V

OUT

100mV/div

AC-COUPLED

I

L

1A/div

Q1, DRAIN

5V/div

MAX668, V

IN

= 5V, V

OUT

= 12V, I

LOAD

= 0.1A,

LOW VOLTAGE, NON-BOOTSTRAPPED

1µs/div

0V

0A

Typical Operating Characteristics (continued)

(Circuits of Figures 2, 3, 4, and 5; TA= +25°C; unless otherwise noted.)

LINE-TRANSIENT RESPONSE

MAX668 toc19

INPUT

VOLTAGE

5V/div

0V

OUTPUT

VOLTAGE

100mV/div

AC-COUPLED

MAX668, V

IN

= 5V TO 8V, V

OUT

= 12V, LOAD = 1.0A,

HIGH VOLTAGE, NON-BOOTSTRAPPED

20ms/div

Detailed Description

The MAX668/MAX669 current-mode PWM controllers
operate in a wide range of DC-DC conversion applica­tions, including boost, SEPIC, flyback, and isolated out­put configurations. Optimum conversion efficiency is
maintained over a wide range of loads by employing
both PWM operation and Maxim’s proprietary Idle
Mode control to minimize operating current at light
loads. Other features include shutdown, adjustable
internal operating frequency or synchronization to an
external clock, soft start, adjustable current limit, and a
wide (1.8V to 28V) input range.

MAX668 vs. MAX669 Differences

Differences between the MAX668 and MAX669 relate
to their use in bootstrapped or non-bootstrapped cir­cuits (Table 1). The MAX668 operates with inputs as
low as 3V and can be connected in

either

a boot­strapped or non-bootstrapped (IC powered from input
supply or other source) configuration. When not boot­strapped, the MAX668 has no restriction on output volt­age. When bootstrapped, the output cannot exceed
28V.

The MAX669 is optimized for low input voltages (down
to 1.8V) and

requires

bootstrapped operation (IC pow-

ered from V

OUT

) with output voltages no greater than

28V. Bootstrapping is required because the MAX669
does not have undervoltage lockout, but instead drives
EXT with an open-loop, 50% duty-cycle start-up oscilla­tor when LDO is below 2.5V. It switches to closed-loop
operation only when LDO exceeds 2.5V. If a non-boot­strapped connection is used with the MAX669 and if
VCC(the input voltage) remains below 2.7V, the output
voltage will soar above the regulation point. Table 2
recommends the appropriate device for each biasing
option.

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

8 _______________________________________________________________________________________

NAME FUNCTION

1 LDO

5V On-Chip Regulator Output. This regulator powers all internal circuitry including the EXT gate driver.
Bypass LDO to GND with a 1µF or greater ceramic capacitor.

2 FREQ

Oscillator Frequency Set Input. A resistor from FREQ to GND sets the oscillator from 100kHz (R

OSC

=

500kΩ) to 500kHz (R

OSC

= 100kΩ). f

OSC

= 5 x 10

10

/ R

OSC

. R

OSC

is still required if an external clock is used

at SYNC/SHDN. (See

SYNC/SHDN and FREQ Inputs

section.)

PIN

3 GND Analog Ground

7 PGND Power Ground for EXT Gate Driver and Negative Current-Sense Input

6 CS+ Positive Current-Sense Input. Connect a current-sense resistor, RCS, between CS+ and PGND.

5 FB Feedback Input. The FB threshold is 1.25V.

4 REF 1.25V Reference Output. REF can source 50µA. Bypass to GND with a 0.22µF ceramic capacitor.

10

SYNC/

SHDN

Shutdown control and Synchronization Input. There are three operating modes:

• SYNC/SHDN low: DC-DC off.

• SYNC/SHDN high: DC-DC on with oscillator frequency set at FREQ by R

OSC

.

• SYNC/SHDN clocked: DC-DC on with operating frequency set by SYNC clock input. DC-DC conversion
cycles initiate on rising edge of input clock.

9 V

CC

Input Supply to On-Chip LDO Regulator. VCCaccepts inputs up to 28V. Bypass to GND with a 0.1µF ceramic
capacitor.

8 EXT External MOSFET Gate-Driver Output. EXT swings from LDO to PGND.

Pin Description

Table 1. MAX668/MAX669 Comparison

MAX668 MAX669

VCCInput
Range

3V to 28V 1.8V to 28V

Operation

Bootstrapped or nonboot­strapped. VCCcan be con­nected to input, output, or
other voltage source such as
a logic supply.

Must be boot­strapped (V

CC

must be connect­ed to boosted out­put voltage, V

OUT

).

Under­voltage
Lockout

IC stops switching for LDO
below 2.5V.

No

Soft-Start Yes

When LDO is
above 2.5V

FEATURE

PWM Controller

The heart of the MAX668/MAX669 current-mode PWM
controller is a BiCMOS multi-input comparator that
simultaneously processes the output-error signal, the
current-sense signal, and a slope-compensation ramp
(Figure 1). The main PWM comparator is direct sum­ming, lacking a traditional error amplifier and its associ­ated phase shift. The direct summing configuration
approaches ideal cycle-by-cycle control over the out­put voltage since there is no conventional error amp in
the feedback path.

In PWM mode, the controller uses fixed-frequency, cur­rent-mode operation where the duty ratio is set by the
input/output voltage ratio (duty ratio = (V

OUT

- VIN) / V

IN

in the boost configuration). The current-mode feedback
loop regulates peak inductor current as a function of
the output error signal.

At light loads the controller enters Idle Mode. During
Idle Mode, switching pulses are provided only as need­ed to service the load, and operating current is mini­mized to provide best light-load efficiency. The
minimum-current comparator threshold is 15mV, or 15%
of the full-load value (I

MAX

) of 100mV. When the con­troller is synchronized to an external clock, Idle Mode
occurs only at very light loads.

Bootstrapped/Non-Bootstrapped Operation

Low-Dropout Regulator (LDO)

Several IC biasing options, including bootstrapped and
non-bootstrapped operation, are made possible by an
on-chip, low-dropout 5V regulator. The regulator input is
at VCC, while its output is at LDO. All MAX668/MAX669
functions, including EXT, are internally powered from
LDO. The VCC-to-LDO dropout voltage is typically
200mV (300mV max at 12mA), so that when VCCis less
than 5.2V, LDO is typically V

CC

- 200mV. When LDO is

in dropout, the MAX668/MAX669 still operate with V

CC

as low as 3V (as long as LDO exceeds 2.7V), but with
reduced amplitude FET drive at EXT. The maximum
VCCinput voltage is 28V.

LDO can supply up to 12mA to power the IC, supply
gate charge through EXT to the external FET, and sup­ply small external loads. When driving particularly large
FETs at high switching rates, little or no LDO current
may be available for external loads. For example, when
switched at 500kHz, a large FET with 20nC gate charge
requires 20nC x 500kHz, or 10mA.

VCCand LDO allow a variety of biasing connections to
optimize efficiency, circuit quiescent current, and full­load start-up behavior for different input and output
voltage ranges. Connections are shown in Figures 2, 3,
4, and 5. The characteristics of each are outlined in
Table 1.

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

_______________________________________________________________________________________ 9

ANTISAT

MUX

LOW-VOLTAGE

START-UP

OSCILLATOR

(MAX669 ONLY)

+A

-A

X6

+C

-C

X1

+S

-S

X1

SLOPE COMPENSATION

SQ

BIAS

OSC OSC

FREQ

SYNC/SHDN

0
1

LDO

PGND

1.25V

REF

EXT

UVLO

V

CC

R1
552k

R2
276k

R3
276k

100mV

15mV

I

MAX

I

MIN

MAIN PWM
COMPARATOR

1.25V

FB

CURRENT SENSE

CS+

MAX668
MAX669

LDO

MAX669 ONLY

R

Figure 1. MAX668/MAX669 Functional Diagram

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

10 ______________________________________________________________________________________

MAX669

LDO

CS+

REF

FREQ

V

CC

SYNC/
SHDN

PGND

FB

GND

N1

EXT

VIN = 1.8V to 12V

C3

0.22µF

C2

0.1µF

C4

1µF

R4
100k
1%

R1

0.02Ω

R2
218k
1%

R3

24.9k
1%

C7

220pF

D1

MBRS340T3

C5
68µF
20V

C6
68µF
20V

C8

0.1µF

3

5

7

6

8

2

4

9

1

10

V

OUT

= 12V @ 0.5A

C1

68µF

20V

L1

4.7µH

IRF7401

Figure 2. MAX669 High-Voltage Bootstrapped Configuration

MAX669

LDO

CS+

REF

FREQ

V

CC

SYNC/
SHDN

PGND

FB

GND

N1

EXT

VIN = 1.8V to 5V

C3

0.22µF

C2

1µF

R4
100k
1%

R1

0.02Ω

R2
75k
1%

R3

24.9k
1%

C7

220pF

D1

MBRS340T3

C4
68µF
10V

C5
68µF
10V

C6

0.1µF

3

5

7

6

8

2

4

9

1

10

V

OUT

= 5V @ 1A

C1

68µF

10V

L1

4.7µH

FDS6680
IRF7401

Figure 3. MAX669 Low-Voltage Bootstrapped Configuration

Bootstrapped Operation

With bootstrapped operation, the IC is powered from
the circuit output (V

OUT

). This improves efficiency
when the input voltage is low, since EXT drives the FET
with a higher gate voltage than would be available from
the low-voltage input. Higher gate voltage reduces the
FET on-resistance, increasing efficiency. Other (unde­sirable) characteristics of bootstrapped operation are
increased IC operating power (since it has a higher
operating voltage) and reduced ability to start up with
high load current at low input voltages. If the input volt-

age range extends below 2.7V, then bootstrapped
operation with the MAX669 is the only option.

With VCCconnected to V

OUT

, as in Figure 2, EXT volt-

age swing is 5V when VCCis 5.2V or more, and V

CC

-

0.2V when VCCis less than 5.2V. If the output voltage
does not exceed 5.5V, the on-chip regulator can be
disabled by connecting VCCto LDO (Figure 3). This
eliminates the LDO forward drop and supplies maxi­mum gate drive to the external FET.

Non-Bootstrapped Operation

With non-bootstrapped operation, the IC is powered
from the input voltage (VIN) or another source, such as
a logic supply. Non-bootstrapped operation (Figure 4)
is recommended (but not required) for input voltages
above 5V, since the EXT amplitude (limited to 5V by
LDO) at this voltage range is no higher than it would be
with bootstrapped operation. Note that non-boot­strapped operation is

required

if the output voltage

exceeds 28V, since this level is too high to safely con-

nect to VCC. Also note that only the MAX668 can be
used with non-bootstrapped operation.

If the input voltage does not exceed 5.5V, the on-chip
regulator can be disabled by connecting VCCto LDO
(Figure 5). This eliminates the regulator forward drop
and supplies the maximum gate drive to the external
FET for lowest on-resistance. Disabling the regulator
also reduces the non-bootstrapped minimum input volt­age from 3V to 2.7V.

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

______________________________________________________________________________________ 11

MAX668

LDO

CS+

REF

FREQ

V

CC

SYNC

/

SHDN

PGND

FB

GND

N1

EXT

VIN = 2.7V to 5.5V

C3

0.22µF

C2

1µF

R4
100k
1%

R1

0.02Ω

R2
218k
1%

R3

24.9k
1%

C7

220pF

D1

MBRS340T3

C4
68µF
20V

C5
68µF
20V

C6

0.1µF

3

5

7

6

8

2

4

9

1

10

V

OUT

= 12V @ 1A

C1

68µF

10V

L1

4.7µH

FDS6680

Figure 5. MAX668 Low-Voltage Non-Bootstrapped Configuration

MAX668

LDO

CS+

REF

FREQ

V

CC

PGND

FB

GND

N1

EXT

VIN = 3V to 12V

C3

0.22µF

C4

1µF

C2

0.1µF

R4
100k
1%

R1

0.02Ω

R2
218k
1%

R3

24.9k
1%

C7

220pF

D1

MBRS340T3

C5
68µF
20V

C6
68µF
20V

C8

0.1µF

3

5

7

6

8

2

4

9

1

10

V

OUT

= 12V @ 1A

C1

68µF

20V

L1

4.7µH

FDS6680

SYNC/
SHDN

Figure 4. MAX668 High-Voltage Non-Bootstrapped Configuration

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

12 ______________________________________________________________________________________

Table 2. Bootstrapped and Non-Bootstrapped Configurations

CONFIGURATION FIGURE

USE

WITH:

INPUT

VOLTAGE

RANGE* (V)

OUTPUT

VOLTAGE

RANGE (V)

COMMENTS

High-Voltage,
Bootstrapped

Figure

2

MAX669 1.8 to 28 3V to 28

Connect VCCto V

OUT

. Provides maximum external
FET gate drive for low-voltage (Input <3V) to high­voltage (output >5.5V) boost circuits. V

OUT

cannot

exceed 28V.

Low-Voltage,
Bootstrapped

Figure

3

MAX669 1.8 to 5.5 2.7 to 5.5

Connect V

OUT

to VCCand LDO. Provides maxi-

mum possible external FET gate drive for low-volt­age designs, but limits V

OUT

to 5.5V or less.

High-Voltage,
Non-Bootstrapped

Figure

4

MAX668 3 to 28 VINto ∞

Connect VINto VCC. Provides widest input and out-

put range, but external FET gate drive is reduced for
V

IN

below 5V.

Low-Voltage,
Non-Bootstrapped

Figure

5

MAX668 2.7 to 5.5 VINto ∞

Connect VINto VCCand LDO. FET gate-drive
amplitude = V

IN

for logic-supply (input 3V to 5.5V) to
high-voltage (output >5.5V) boost circuits. IC oper­ating power is less than in Figure 4, since IC current
does not pass through the LDO regulator.

Extra IC supply,
Non-Bootstrapped

None MAX668

Not

Restricted

VINto ∞

Connect VCC and LDO to a separate supply
(V

BIAS

) that powers only the IC. FET gate-drive

amplitude = V

BIAS

. Input power source (V

IN)

and

output voltage range (V

OUT

) are not restricted,

except that V

OUT

must exceed VIN.

In addition to the configurations shown in Table 2, the
following guidelines may help when selecting a config­uration:

1) If VINis ever below 2.7V, V

CC

must

be boot-

strapped to V

OUT

and the MAX669 must be used. If

V

OUT

never exceeds 5.5V, LDO may be shorted to

VCCand V

OUT

to eliminate the dropout voltage of

the LDO regulator.

2) If VINis greater than 3.0V, VCCcan be powered
from VIN, rather than from V

OUT

(non-bootstrapped).
This can save quiescent power consumption, espe­cially when V

OUT

is large. If VINnever exceeds

5.5V, LDO may be shorted to VCCand VINto elimi­nate the dropout voltage of the LDO regulator.

3) If VINis in the 3V to 4.5V range (i.e., 1-cell Li-Ion or
3-cell NiMH battery range), bootstrapping VCCfrom
V

OUT

, although not required, may increase overall
efficiency by increasing gate drive (and reducing
FET resistance) at the expense of quiescent power
consumption.

4) If VINalways exceeds 4.5V, VCCshould be tied to
VIN, since bootstrapping from V

OUT

does not
increase gate drive from EXT but does increase
quiescent power dissipation.

*

For standard step-up DC-DC circuits (as in Figures 2, 3, 4, and 5), regulation cannot be maintained if VINexceeds V

OUT

. SEPIC

and transformer-based circuits do not have this limitation.

SYNC/

SHDN

and FREQ Inputs

The SYNC/SHDN pin provides both external-clock syn­chronization (if desired) and shutdown control. When
SYNC/SHDN is low, all IC functions are shut down. A
logic high at SYNC/SHDN selects operation at a fre­quency set by R

OSC

, connected from FREQ to GND.

The relationship between f

OSC

and R

OSC

is:

R

OSC

= 5 x 10

10

/ f

OSC

So a 500kHz operating frequency, for example, is set
with R

OSC

= 100kΩ.

Rising clock edges on SYNC/SHDN are interpreted as
synchronization inputs. If the sync signal is lost while
SYNC/SHDN is high, the internal oscillator takes over at
the end of the last cycle and the frequency is returned
to the rate set by R

OSC

. If sync is lost with SYNC/SHDN
low, the IC waits for 70µs before shutting down. This
maintains output regulation even with intermittent sync
signals. When an external sync signal is used, Idle
Mode switchover at the 15mV current-sense threshold
is disabled so that Idle Mode only occurs at very light
loads. Also, R

OSC

should be set for a frequency 15%

below the SYNC clock rate:

R

OSC(SYNC)

= 5 x 10

10

/ (0.85 x f

SYNC

)

Soft-Start

The MAX668/MAX669 feature a “digital” soft start which
is preset and requires no external capacitor. Upon
start-up, the peak inductor increments from 1/5 of the
value set by RCS, to the full current-limit value, in five
steps over 1024 cycles of f

OSC

or f

SYNC

. For example,

with an f

OSC

of 200kHz, the complete soft-start

sequence takes 5ms. See the

Typical Operating

Characteristics

for a photo of soft-start operation. Soft­start is implemented: 1) when power is first applied to
the IC, 2) when exiting shutdown with power already
applied, and 3) when exiting undervoltage lockout. The
MAX669’s soft-start sequence does not start until LDO
reaches 2.5V.

Design Procedure

The MAX668/MAX669 can operate in a number of DC­DC converter configurations including step-up, SEPIC
(single-ended primary inductance converter), and fly­back. The following design discussions are limited to
step-up, although SEPIC and flyback examples are
shown in the

Application Circuits

section.

Setting the Operating Frequency

The MAX668/MAX669 can be set to operate from
100kHz to 500kHz. Choice of operating frequency will
depend on number of factors:

1) Noise considerations may dictate setting (or syn­chronizing) f

OSC

above or below a certain frequency
or band of frequencies, particularly in RF applica­tions.

2) Higher frequencies allow the use of smaller value
(hence smaller size) inductors and capacitors.

3) Higher frequencies consume more operating power
both to operate the IC and to charge and discharge
the gate of the external FET. This tends to reduce
efficiency at light loads; however, the MAX668/
MAX669’s Idle Mode feature substantially increases
light-load efficiency.

4) Higher frequencies may exhibit poorer overall effi­ciency due to more transition losses in the FET;
however, this shortcoming can often be nullified by
trading some of the inductor and capacitor size
benefits for lower-resistance components.

The oscillator frequency is set by a resistor, R

OSC

, con-

nected from FREQ to GND. R

OSC

must be connected

whether or not the part is externally synchronized R

OSC

is in each case:

R

OSC

= 5 x 1010/ f

OSC

when

not

using an external clock.

R

OSC(SYNC)

= 5 x 10

10

/ (0.85 x f

SYNC

)

when using an external clock, f

SYNC

.

Setting the Output Voltage

The output voltage is set by two external resistors (R2
and R3, Figures 2, 3, 4, and 5). First select a value for
R3 in the 10kΩ to 1MΩ range. R2 is then given by:

R2 = R3 [(V

OUT

/ V

REF

) – 1]

where V

REF

is 1.25V.

Determining Inductance Value

For most MAX668/MAX669 boost designs, the inductor
value (L

IDEAL

) can be derived from the following equa­tion, which picks the optimum value for stability based
on the MAX668/MAX669’s internally set slope compen­sation:

L

IDEAL

= V

OUT

/ (4 x I

OUT

x f

OSC

)

The MAX668/MAX669 allow significant latitude in induc­tor selection if L

IDEAL

is not a convenient value. This

may happen if L

IDEAL

is a not a standard inductance

(such as 10µH, 22µH, etc.), or if L

IDEAL

is too large to
be obtained with suitable resistance and saturation-cur­rent rating in the desired size. Inductance values small­er than L

IDEAL

may be used with no adverse stability
effects; however, the peak-to-peak inductor current
(I

LPP

) will rise as L is reduced. This has the effect of

raising the required I

LPK

for a given output power and

also requiring larger output capacitance to maintain a

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

______________________________________________________________________________________ 13

MAX668/MAX669

given output ripple. An inductance value larger than
L

IDEAL

may also be used, but output-filter capacitance
must be increased by the same proportion that L has to
L

IDEAL

. See the

Capacitor Selection

section for more

information on determining output filter values.
Due the MAX668/MAX669’s high switching frequencies,

inductors with a ferrite core or equivalent are recom­mended. Powdered iron cores are

not

recommended

due to their high losses at frequencies over 50kHz.

Determining Peak Inductor Current

The peak inductor current required for a particular out­put is:

I

LPEAK

= I

LDC

+ (I

LPP

/ 2)

where I

LDC

is the average DC input current and I

LPP

is

the inductor peak-to-peak ripple current. The I

LDC

and

I

LPP

terms are determined as follows:

where VDis the forward voltage drop across the
Schottky rectifier diode (D1), and VSWis the drop
across the external FET, when on.

where L is the inductor value. The saturation rating of
the selected inductor should meet or exceed the calcu­lated value for I

LPEAK

, although most coil types can be
operated up to 20% over their saturation rating without
difficulty. In addition to the saturation criteria, the induc­tor should have as low a series resistance as possible.
For continuous inductor current, the power loss in the
inductor resistance, PLR, is approximated by:

P

LR

≅ (I

OUT

x V

OUT

/ VIN)2x R

L

where RLis the inductor series resistance.
Once the peak inductor current is selected, the current-

sense resistor (RCS) is determined by:

RCS= 85mV / I

LPEAK

For high peak inductor currents (>1A), Kelvin sensing
connections should be used to connect CS+ and
PGND to RCS. PGND and GND should be tied together
at the ground side of RCS.

Power MOSFET Selection

The MAX668/MAX669 drive a wide variety of N-channel
power MOSFETs (NFETs). Since LDO limits the EXT
output gate drive to no more than 5V, a logic-level
NFET is required. Best performance, especially at low
input voltages (below 5V), is achieved with low-thresh-

old NFETs that specify on-resistance with a gate­source voltage (VGS) of 2.7V or less. When selecting an
NFET, key parameters can include:

1) Total gate charge (Qg)

2) Reverse transfer capacitance or charge (C

RSS

)

3) On-resistance (R

DS(ON)

)

4) Maximum drain-to-source voltage (V

DS(MAX)

)

5) Minimum threshold voltage (V

TH(MIN)

)

At high switching rates, dynamic characteristics (para­meters 1 and 2 above) that predict switching losses
may have more impact on efficiency than R

DS(ON),

which predicts DC losses. Qgincludes all capacitances
associated with charging the gate. In addition, this
parameter helps predict the current needed to drive the
gate at the selected operating frequency. The continu­ous LDO current for the FET gate is:

I

GATE

= Qgx f

OSC

For example, the MMFT3055L has a typical Qgof 7nC
(at V

GS

= 5V); therefore, the I

GATE

current at 500kHz is

3.5mA. Use the FET manufacturer’s

typical

value for Q

g

in the above equation, since a maximum value (if sup­plied) is usually too conservative to be of use in esti­mating I

GATE

.

Diode Selection

The MAX668/MAX669’s high switching frequency
demands a high-speed rectifier. Schottky diodes are
recommended for most applications because of their
fast recovery time and low forward voltage. Ensure that
the diode’s average current rating is adequate using
the diode manufacturer’s data, or approximate it with
the following formula:

Also, the diode reverse breakdown voltage must
exceed V

OUT

. For high output voltages (50V or above),
Schottky diodes may not be practical because of this
voltage requirement. In these cases, use a high-speed
silicon rectifier with adequate reverse voltage.

Capacitor Selection

Output Filter Capacitor

The minimum output filter capacitance that ensures sta­bility is:

where V

IN(MIN)

is the minimum expected input voltage.

Typically C

OUT(MIN)

, though sufficient for stability, will

C

(7.5V x L / L )

(2 R x V x f )

OUT(MIN)

IDEAL

CS IN(MIN) OSC

=

π

II

I- I

3

DIODE OUT

LPEAK OUT

=+

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

14 ______________________________________________________________________________________

I =

I (V + V

(V – V

LDC

OUT OUT D

IN SW

)

)

I =

(V – V ) (V + V – V )

L x f (V + V )

LPP

IN SW OUT D IN

OSC OUT D

not be adequate for low output voltage ripple. Since
output ripple in boost DC-DC designs is dominated by
capacitor equivalent series resistance (ESR), a capaci­tance value 2 or 3 times larger than C

OUT(MIN)

is typi­cally needed. Low-ESR types must be used. Output
ripple due to ESR is:

V

RIPPLE(ESR)

= I

LPEAK

x ESR

COUT

Input Capacitor

The input capacitor (CIN) in boost designs reduces the
current peaks drawn from the input supply and reduces
noise injection. The value of CINis largely determined
by the source impedance of the input supply. High
source impedance requires high input capacitance,
particularly as the input voltage falls. Since step-up DC­DC converters act as “constant-power” loads to their
input supply, input current rises as input voltage falls.
Consequently, in low-input-voltage designs, increasing
CINand/or lowering its ESR can add as many as five
percentage points to conversion efficiency. A good
starting point is to use the same capacitance value for
CINas for C

OUT

.

Bypass Capacitors

In addition to CINand C

OUT

, three ceramic bypass
capacitors are also required with the MAX668/MAX669.
Bypass REF to GND with 0.22µF or more. Bypass LDO
to GND with 1µF or more. And bypass VCCto GND with

0.1µF or more. All bypass capacitors should be located
as close to their respective pins as possible.

Compensation Capacitor

Output ripple voltage due to C

OUT

ESR affects loop
stability by introducing a left half-plane zero. A small
capacitor connected from FB to GND forms a pole with
the feedback resistance that cancels the ESR zero. The
optimum compensation value is:

where R2 and R3 are the feedback resistors (Figures 2,
3, 4, and 5). If the calculated value for CFBresults in a
non-standard capacitance value, values from 0.5C

FB

to

1.5C

FB

will also provide sufficient compensation.

Applications Information

Starting Under Load

In non-bootstrapped configurations (Figures 4 and 5),
the MAX668 can start up with any combination of out­put load and input voltage at which it can operate when
already started. In other words, there are no special
limitations to start-up in non-bootstrapped circuits.

In bootstrapped configurations with the MAX668 or
MAX669, there may be circumstances where full load
current can only be applied after the circuit has started
and the output is near its set value. As the input voltage
drops, this limitation becomes more severe. This char­acteristic of all bootstrapped designs occurs when the
MOSFET gate is not fully driven until the output voltage
rises. This is problematic because a heavily loaded out­put cannot rise until the MOSFET has low on-resis­tance. In such situations, low-threshold FETs (V

TH

<

V

IN(MIN)

) are the most effective solution. The

Typical

Operating Characteristics

section shows plots of start­up voltage versus load current for a typical boot­strapped design.

Layout Considerations

Due to high current levels and fast switching waveforms
that radiate noise, proper PC board layout is essential.
Protect sensitive analog grounds by using a star ground
configuration. Minimize ground noise by connecting
GND, PGND, the input bypass-capacitor ground lead,
and the output-filter ground lead to a single point (star
ground configuration). Also, minimize trace lengths to
reduce stray capacitance, trace resistance, and radiat­ed noise. The trace between the external gain-setting
resistors and the FB pin must be extremely short, as
must the trace between GND and PGND.

Application Circuits

Low-Voltage Boost Circuit

Figure 3 shows the MAX669 operating in a low-voltage
boost application. The MAX669 is configured in the
bootstrapped mode to improve low input voltage per­formance. The IRF7401 N-channel MOSFET was select­ed for Q1 in this application because of its very low

0.7V gate threshold voltage (VGS). This circuit provides
a 5V output at greater than 2A of output current and
operates with input voltages as low as 1.8V. Efficiency
is typically in the 85% to 90% range.

+12V Boost Application

Figure 5 shows the MAX668 operating in a 5V to 12V
boost application. This circuit provides output currents
of greater than 1A at a typical efficiency of 92%. The
MAX668 is operated in non-bootstrapped mode to mini­mize the input supply current. This achieves maximum
light-load efficiency. If input voltages below 5V are
used, the IC should be operated in bootstrapped mode
to achieve best low-voltage performance.

4-Cell to +5V SEPIC Power Supply

Figure 6 shows the MAX668 in a SEPIC (single-ended
primary inductance converter) configuration. This con­figuration is useful when the input voltage can be either

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

______________________________________________________________________________________ 15

C C x

ESR

(R2 x R3) / (R2 + R3)

FB OUT

COUT

=

MAX668/MAX669

larger or smaller than the output voltage, such as when
converting four NiMH, NiCd, or Alkaline cells to a 5V
output. The SEPIC configuration is often a good choice
for combined step-up/step-down applications.

The N-channel MOSFET (Q1) must be selected to with­stand a drain-to-source voltage (VDS) greater than the
sum of the input and output voltages. The coupling
capacitor (C2) must be a low-ESR type to achieve max­imum efficiency. C2 must also be able to handle high
ripple currents; ordinary tantalum capacitors should not
be used for high-current designs.

The circuit in Figure 6 provides greater than 1A output
current at 5V when operating with an input voltage from
3V to 25V. Efficiency will typically be between 70% and
85%, depending upon the input voltage and output cur­rent.

Isolated +5V to +5V Power Supply

The circuit of Figure 7 provides a 5V isolated output at
400mA from a 5V input power supply. Transformer T1
provides electrical isolation for the forward path of the
converter, while the TLV431 shunt regulator and
MOC211 opto-isolator provide an isolated feedback
error voltage for the converter. The output voltage is set
by resistors R2 and R3 such that the mid-point of the
divider is 1.24V (threshold of TLV431). Output voltage
can be adjusted from 1.24V to 6V by selecting the
proper ratio for R2 and R3. For output voltages greater
than 6V, substitute the TL431 for the TLV431, and use

2.5V as the voltage at the midpoint of the voltage­divider.

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

16 ______________________________________________________________________________________

R3

100k

R4

0.02Ω

R1
75k

R2
25k

C4

520pF

V

IN

3V to 25V

30V
FDS6680

Q1

L1

CTX5-4

MAX668

SHDNV

CC

910

LDO

FREQ

D1: MBR5340T3, 3A, 40V SCHOTTKY DIODE
R4: WSL-2512-R020F, 0.02Ω
C3: AVX TPSZ686M020R0150, 68µF, 150mΩ ESR

REF

EXT

CS+

8

6

PGNDGND

73

FB

1

2

4

5

1µF

22µF x 3

@ 35V

C3
68µF x 3

V

OUT

5V @ 1A

4.9µH

C2

10µF @ 35V

D1

40V

0.22µF

Figure 6. MAX668 in SEPIC Configuration

Chip Information

TRANSISTOR COUNT: 1861

MAX668/MAX669

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

______________________________________________________________________________________ 17

MAX668

LDO

CS+

FB

SHDN

PGND

FREQREF

V

CC

GND

T1

2:1

EXT

VIN = +5V

T1: COILTRONICS CTX03-14232

+5V @ 400mA

+5V RETURN

0.1Ω

R2
301k
1%

510Ω

TLV431

610Ω0.068µF

R3
100k
1%

MBR0540L

MBR0540L

47µH

220µF

10V

0.22µF

1µF

100k

10k

MOC211

IRF7603

220µF

10V

0.1µF

Figure 7. Isolated +5V to +5V at 400mA Power Supply

MAX668/MAX669

Package Information

1.8V to 28V Input, PWM Step-Up
Controllers in µMAX

18 ______________________________________________________________________________________

10LUMAXB.EPS