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MAX668EUB+-MAX668EUB+T-MAX669EUB+
1.8V to 28V Input, PWM Step-Up Controllers in µMAX
General DescriptionThe MAX668/MAX669 constant-frequency, pulse-width-
modulating (PWM), current-mode DC-DC controllers are
designed for a wide range of DC-DC conversion applications
including step-up, SEPIC, flyback, and isolated-output
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 boot-
strapped or non-bootstrapped (IC powered from input sup-
ply or other source) configuration. When not bootstrapped,
it has no restriction on output voltage. Both ICs are avail-able in an extremely compact 10-pin μMAX package.
Beneits and 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
Idle Mode is a trademark of Maxim Integrated Products.
+ Denotes a lead(Pb)-free/RoHS-compliant package.
T = Tape and reel.
/V Denotes an automotive qualified part.
Note: Devices are also available in a lead(Pb)-free/RoHS-compliant package. Specify lead-free by adding “+” to the part
number when ordering.
PARTTEMP RANGEPIN-PACKAGE
MAX668EUB-40°C to +85°C10 µMAX
MAX669EUB-40°C to +85°C10 µMAX
MAX669EUB/V+T-40°C to +85°C10 µMAX
MAX669FREQCS+
SYNC/
SHDN
PGND
GND
VCCEXT
LDO
REF
VOUT = 28V
VIN = 1.8V to 28V
SYNC/SHDN
VCC
EXT
PGNDREF
GND
FREQ
LDO
MAX668
MAX669µMAX
TOP VIEW
CS+FB
MAX668/MAX6691.8V to 28V Input, PWM Step-UpControllers in μMAX
Typical Operating CircuitPin Coniguration
Ordering Information
VCC 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 (VLDO + 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 (TA = +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
Soldering Temperature (Reflow) ......................................+300°C
Lead(Pb)-Free Packages ................................................+260°C
Packages Containing Lead(Pb).......................................+240°C
(VCC = VLDO = +5V, ROSC = 200kΩ, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETERCONDITIONSMINTYPMAXUNITS
PWM CONTROLLERInput Voltage Range, VCCMAX668328VMAX6691.828
Input Voltage Range with VCC Tied to LDO2.75.5V
FB Threshold1.2251.2501.275V
FB Threshold Load Regulation
Typically 0.013% per mV on CS+;
VCS+ range is 0 to 100mV for 0 to full load
current.
0.013%/mV
FB Threshold Line Regulation
Typically 0.012% per % duty factor on
EXT; EXT duty factor for a step-up is:
100% (1 – VIN/VOUT)
0.012%/%
FB Input CurrentVFB = 1.30V120nA
Current Limit Threshold85100115mV
Idle Mode Current-Sense Threshold51525mV
CS+ Input CurrentCS+ forced to GND0.21µA
VCC Supply Current (Note 1)VFB = 1.30V, VCC = 3V to 28V220350µA
Shutdown Supply Current (VCC)SYNC/SHDN = GND, VCC = 28V3.56µA
REFERENCE AND LDO REGULATORSLDO Output VoltageLDO load = ∞ to 400Ω
5V ≤ VCC ≤ 28V
(includes LDO dropout)4.505.005.503V ≤ VCC ≤ 28V
(includes LDO dropout)2.655.50
Undervoltage Lockout ThresholdSensed at LDO, falling edge,
hysteresis = 1%, MAX668 only2.402.502.60V
REF Output VoltageNo load, CREF = 0.22μF1.2251.2501.275V
REF Load RegulationREF load = 0 to 50μA-2-10mV
REF Undervoltage Lockout ThresholdRising edge, 1% hysteresis1.01.11.2V
OSCILLATOROscillator Frequency
ROSC = 200kΩ ±1%225250275
kHzROSC = 100kΩ ±1%425500575
MAX668/MAX6691.8V to 28V Input, PWM Step-UpControllers in μMAX
Absolute Maximum Ratings
Electrical Characteristics
(VCC = VLDO = +5V, ROSC = 200kΩ, TA = -40°C to +85°C, unless otherwise noted.) (Note 2)
(VCC = VLDO = +5V, ROSC = 200kΩ, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.)
PARAMETERCONDITIONSMINTYPMAXUNITSMaximum Duty Cycle
ROSC = 200kΩ ±1%879093ROSC = 100kΩ ±1%869094
ROSC = 500kΩ ±1%869094
Minimum EXT Pulse Width290ns
Minimum SYNC Input-Pulse Duty Cycle2045%
Minimum SYNC Input Low Pulse Width50200ns
SYNC Input Rise/Fall TimeNot tested200ns
SYNC Input Frequency Range100500kHz
SYNC/SHDN Falling Edge to Shutdown
Delay70µs
SYNC/SHDN Input High Voltage3.0V < VCC < 28V2.0V1.8V < VCC < 3.0V (MAX669)1.5
SYNC/SHDN Input Low Voltage3.0V < VCC < 28V0.45V1.8V < VCC < 3.0V (MAX669)0.30
SYNC/SHDN Input CurrentVSYNC/SHDN = 5V0.53.0µAVSYNC/SHDN = 28V1.56.5
EXT Sink/Source CurrentEXT forced to 2V1A
EXT On-ResistanceEXT high or low25Ω
PARAMETERCONDITIONSMINMAXUNITS
PWM CONTROLLERInput Voltage Range, VCCMAX668328VMAX6691.828
Input Voltage Range with VCC Tied to LDO2.75.5V
FB Threshold1.221.28V
FB Input CurrentVFB = 1.30V20nA
Current-Limit Threshold85115mV
Idle Mode Current-Sense Threshold327mV
CS+ Input CurrentCS+ forced to GND1µA
VCC Supply Current (Note 1)VFB = 1.30V, VCC = 3V to 28V350µA
Shutdown Supply Current (VCC)SYNC/SHDN = GND, VCC = 28V6µA
REFERENCE AND LDO REGULATORSLDO Output VoltageLDO load = ∞ to 400Ω
5V ≤ VCC ≤ 28V
(includes LDO dropout)4.505.503V ≤ VCC ≤ 28V
(includes LDO dropout)2.655.50Sensed at LDO, falling edge,
MAX668/MAX6691.8V to 28V Input, PWM Step-UpControllers in μMAX
Electrical Characteristics
Electrical Characteristics (continued)
(VCC = VLDO = +5V, ROSC = 200kΩ, TA = -40°C to +85°C, unless otherwise noted.) (Note 2)
Note 1: This is the VCC current consumed when active but not switching. Does not include gate-drive current.
Note 2: Limits at TA = -40°C are guaranteed by design.
PARAMETERCONDITIONSMINMAXUNITSREF Output VoltageNo load, CREF = 0.22μF1.221.28V
REF Load RegulationREF load = 0 to 50μA-10mV
REF Undervoltage Lockout ThresholdRising edge, 1% hysteresis1.01.2V
OSCILLATOROscillator Frequency
ROSC = 200kΩ ±1%222278
kHzROSC = 100kΩ ±1%425575
ROSC = 500kΩ ±1%85115
Maximum Duty Cycle
ROSC = 200kΩ ±1%8793ROSC = 100kΩ ±1%8694
ROSC = 500kΩ ±1%8694
Minimum SYNC Input-Pulse Duty Cycle45%
Minimum SYNC Input Low Pulse Width200ns
SYNC Input Rise/Fall TimeNot tested200ns
SYNC Input Frequency Range100500kHz
SYNC/SHDN Input High Voltage3.0V < VCC < 28V2.0V1.8V < VCC < 3.0V (MAX669)1.5
SYNC/SHDN Input Low Voltage3.0V < VCC < 28V0.45V1.8V < VCC < 3.0V (MAX669)0.30
SYNC/SHDN Input CurrentVSYNC/SHDN = 5V3.0µAVSYNC/SHDN = 28V6.5
EXT On-ResistanceEXT high or low5Ω
MAX668/MAX6691.8V to 28V Input, PWM Step-UpControllers in μMAX
Electrical Characteristics (continued)
(Circuits of Figures 2, 3, 4, and 5; TA = +25°C; unless otherwise noted.)10,000100010100
MAX668 EFFICIENCY vs.
LOAD CURRENT (VOUT = 12V)MAX668 toc02
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = 5V
NON-BOOTSTRAPPED
FIGURE 4
R4 = 200kΩ
MAX668 EFFICIENCY vs.
LOAD CURRENT (VOUT = 24V)MAX668 toc03
LOAD CURRENT (mA)
EFFICIENCY (%)10,000100010100VIN = 8V
VIN = 5V
VIN = 12V
NON-BOOTSTRAPPED
FIGURE 4
R4 = 200kΩ
MAX669 MINIMUM START-UP VOLTAGE
vs. LOAD CURRENT
MAX668 toc04
LOAD CURRENT (mA)
MINIMUM START-UP VOLTAGE (V)
VOUT = 5V
VOUT = 12V
BOOTSTRAPPED
FIGURE 2
SUPPLY CURRENT vs.
SUPPLY VOLTAGE
MAX668 toc05
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (µA)
MAX669
MAX668
CURRENT INTO VCC PIN
ROSC = 500kΩ
NO-LOAD SUPPLY CURRENT vs.
SUPPLY VOLTAGE
MAX668 toc06
SUPPLY VOLTAGE (V)
NO-LOAD SUPPLY CURRENT (µA)
VOUT = 12V
BOOTSTRAPPED
FIGURE 2
R4 = 200kΩ
SHUTDOWN CURRENT vs.
SUPPLY VOLTAGE
MAX668 toc07
SHUTDOWN CURRENT (µA)1.0
CURRENT INTO VCC PIN
MAX668
MAX66910100100010,000
EFFICIENCY vs. LOAD CURRENT
(VOUT = 5V)MAX668 toc01
LOAD CURRENT (mA)
EFFICIENCY (%)
VIN = 3.3V
VIN = 3.6V
VIN = 2V
VIN = 2.7V
BOOTSTRAPPED
FIGURE 3
R4 = 200kΩ
SUPPLY CURRENT vs.
TEMPERATURE
MAX668 toc08
SUPPLY CURRENT (µA)
ROSC = 100kΩ
ROSC = 200kΩ
ROSC = 500kΩ
LDO DROPOUT VOLTAGE vs.
LDO CURRENT
MAX668 toc09
LDO DROPOUT VOLTAGE (mV)
VIN = 3V
VIN = 4.5V
MAX668/MAX6691.8V to 28V Input, PWM Step-UpControllers in μMAX
Typical Operating Characteristics
(Circuits of Figures 2, 3, 4, and 5; TA = +25°C; unless otherwise noted.)
REFERENCE VOLTAGE vs.
TEMPERATURE
MAX668 toc10
TEMPERATURE (°C)
REFERENCE VOLTAGE (V)
VCC = 5V
SWITCHING FREQUENCY vs. ROSC
MAX668 toc11
ROSC (kΩ)
SWITCHING FREQUENCY (kHz)
VCC = 5V
SWITCHING FREQUENCY vs.
TEMPERATURE
MAX668 toc12
TEMPERATURE (°C)
SWITCHING FREQUENCY (kHz)
100kΩ
165kΩ
499kΩ
VIN = 5V
100100010,000
EXT RISE/FALL TIME vs.
CAPACITANCEMAX668 toc13
CAPACITANCE (pF)
EXT RISE/FALL TIME (ns)
tR, VCC = 3.3V
tF, VCC = 3.3V
tR, VCC = 5V
tF, VCC = 5V
MAX668/MAX6691.8V to 28V Input, PWM Step-UpControllers in μMAX
Typical Operating Characteristics (continued)
(Circuits of Figures 2, 3, 4, and 5; TA = +25°C; unless otherwise noted.)
EXITING SHUTDOWNMAX668 toc14
OUTPUT
VOLTAGE
5V/div
INDUCTOR
CURRENT
2A/div
SHUTDOWN
VOLTAGE
5V/div
MAX668, VIN = 5V, VOUT = 12V, LOAD = 1.0A, ROSC = 100kW,
LOW VOLTAGE, NON-BOOTSTRAPPED
500ms/div
ENTERING SHUTDOWNMAX668 toc15
OUTPUT
VOLTAGE
5V/div
SHUTDOWN
VOLTAGE
5V/div
MAX668, VIN = 5V, VOUT = 12V, LOAD = 1.0A,
LOW VOLTAGE, NON-BOOTSTRAPPED
200µs/div
HEAVY-LOAD SWITCHING WAVEFORMMAX668 toc16
VOUT
200mV/div
AC-COUPLED
1A/div
Q1, DRAIN
5V/div
MAX668, VIN = 5V, VOUT = 12V, ILOAD = 1.0A,
LOW VOLTAGE, NON-BOOTSTRAPPED
1µs/div
LIGHT-LOAD SWITCHING WAVEFORMMAX668 toc17
VOUT
100mV/div
AC-COUPLED
1A/div
Q1, DRAIN
5V/div
MAX668, VIN = 5V, VOUT = 12V, ILOAD = 0.1A,
LOW VOLTAGE, NON-BOOTSTRAPPED
1µs/div
LOAD-TRANSIENT RESPONSEMAX668 toc18OUTPUT
VOLTAGE
AC-COUPLED
100mV/div
LOAD
CURRENT
1A/div
MAX668, VIN = 5V, VOUT = 12V, ILOAD = 0.1A TO 1.0A,
1ms/div
LINE-TRANSIENT RESPONSEMAX668 toc19
INPUT
VOLTAGE
5V/div
OUTPUT
VOLTAGE
100mV/div
AC-COUPLED
MAX668, VIN = 5V TO 8V, VOUT = 12V, LOAD = 1.0A,
20ms/div
MAX668/MAX6691.8V to 28V Input, PWM Step-UpControllers in μMAX
Typical Operating Characteristics (continued)
Detailed DescriptionThe 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 DifferencesDifferences 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 boot-
strapped, the output cannot exceed 28V.
The MAX669 is optimized for low input voltages (down to
1.8V) and requires bootstrapped operation (IC powered
from VOUT) 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.
Table 1. MAX668/MAX669 Comparison
PINNAMEFUNCTIONLDO5V 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.FREQOscillator Frequency Set Input. A resistor from FREQ to GND sets the oscillator from 100kHz (ROSC =500kΩ) to 500kHz (ROSC = 100kΩ). fOSC = 5 x 1010 / ROSC. ROSC is still required if an external clock is used
at SYNC/SHDN. (See SYNC/SHDN and FREQ Inputs section.)GNDAnalog GroundREF1.25V Reference Output. REF can source 50µA. Bypass to GND with a 0.22µF ceramic capacitor.FBFeedback Input. The FB threshold is 1.25V.CS+Positive Current-Sense Input. Connect a current-sense resistor, RCS, between CS+ and PGND.PGNDPower Ground for EXT Gate Driver and Negative Current-Sense InputEXTExternal MOSFET Gate-Driver Output. EXT swings from LDO to PGND.VCCInput Supply to On-Chip LDO Regulator. VCC accepts inputs up to 28V. Bypass to GND with a 0.1µF ceramic
capacitor.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 ROSC.• 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.
FEATUREMAX668MAX669VCC Input
Range3V to 28V1.8V to 28V
Operation
Bootstrapped or nonboot-
strapped. VCC can be
connected to input,
output, or other voltage
source such as a logic
supply.
Must be boot-
strapped (VCC must
be connected to
boosted output
voltage, VOUT).
Under-
voltage
Lockout
IC stops switching for
LDO below 2.5V.No
Soft-StartYesWhen LDO is
above 2.5V
MAX668/MAX6691.8V to 28V Input, PWM Step-UpControllers in μMAX
Pin Description
PWM ControllerThe 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 = (VOUT - VIN)/VIN
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 (IMAX) of 100mV. When the controller is synchro-
nized 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 VCC is less than
5.2V, LDO is typically VCC - 200mV. When LDO is in drop-
out, the MAX668/MAX669 still operate with VCC as low
as 3V (as long as LDO exceeds 2.7V), but with reduced
amplitude FET drive at EXT. The maximum VCC input
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.
VCC and LDO allow a variety of biasing connections to
optimize efficiency, circuit quiescent current, and full-load
start-up behavior for different input and output voltage
ranges. Connections are shown in Figure 2, Figure 3,
Figure 4, and Figure 5. The characteristics of each are
outlined in Table 1.
ANTISATMUXLOW-VOLTAGE
START-UP
OSCILLATOR
(MAX669 ONLY)X6X1X1SLOPE COMPENSATION
S Q
BIAS
OSCOSCFREQ
SYNC/SHDN
LDO
PGND
1.25V
REF
EXT
UVLO
VCC
552k
276k
276k
100mV
15mV
IMAX
IMIN
MAIN PWM
COMPARATOR
1.25V
CURRENT SENSECS+
MAX668
MAX669LDO
MAX669 ONLY
MAX668/MAX6691.8V to 28V Input, PWM Step-UpControllers in μMAX
