MAX767CAP ,5V-to-3.3V, Synchronous, Step-Down Power-Supply ControllerMAX76719-0224; Rev 2; 8/945V-to-3.3V, Synchronous, Step-Down Power-Supply Controller_______________
MAX767CAP+ ,5V to 3.3V Output, Synchronous, Step-Down Power Supply ControllerApplicationsPART TEMP. RANGEPACKAGE TOL (V)Local 5V-to-3.3V DC-DC ConversionMAX767CAP 0°C to +70°C ..
MAX767CAP-T ,5V to 3.3V Output, Synchronous, Step-Down Power Supply Controllerfeatures set♦ 120µA Standby Supply Currentthis device apart from similar, low-voltage step-down♦ 4. ..
MAX767EAP ,5V-to-3.3V, Synchronous, Step-Down Power-Supply ControllerMAX76719-0224; Rev 2; 8/945V-to-3.3V, Synchronous, Step-Down Power-Supply Controller_______________
MAX767EAP+ ,5V to 3.3V Output, Synchronous, Step-Down Power Supply ControllerFeatures♦ >90% EfficiencyThe MAX767 is a high-efficiency, synchronous buckcontroller IC dedicated t ..
MAX767EAP-T ,5V to 3.3V Output, Synchronous, Step-Down Power Supply ControllerMAX76719-0224; Rev 3; 7/005V-to-3.3V, Synchronous, Step-Down Power-Supply Controller________________
MB6M ,MINIATURE GLASS PASSIVATED SINGLE-PHASE BRIDGE RECTIFIERThermal Characteristics (TA = 25°C unless otherwise noted)Parameter Symbol MB2M MB4M MB6M UnitDevic ..
MB6S ,Bridge RectifiersThermal Characteristics (T = 25°C unless otherwise noted)AParameter Symbol MB2S MB4S MB6S UnitDevic ..
MB7117E , Schottky TTL 2048-Bit Bipolar Programmable Read-Only Memory
MB71A38-25 , PROGRAMMABLE SCHOTTKY 16384-BIT READ ONLY MEMORY
MAX767CAP-MAX767EAP-MAX767RCAP-MAX767TCAP-MAX767TEAP
5V-to-3.3V, Synchronous, Step-Down Power-Supply Controller
_______________General DescriptionThe MAX767 is a high-efficiency, synchronous buck
controller IC dedicated to converting a fixed 5V supply
into a tightly regulated 3.3V output. Two key features set
this device apart from similar, low-voltage step-down
switching regulators: high operating frequency and all
N-channel construction in the application circuit. The
300kHz operating frequency results in very small, low-
cost external surface-mount components.
The inductor, at 3.3µH for 5A, is physically at least five
times smaller than inductors found in competing solu-
tions. All N-channel construction and synchronous rectifi-
cation result in reduced cost and highest efficiency.
Efficiency exceeds 90% over a wide range of loading,
eliminating the need for heatsinking. Output capacitance
requirements are low, reducing board space and cost.
The MAX767 is a monolithic BiCMOS IC available in
20-pin SSOP packages. For other fixed output voltages
and package options, please consult the factory.
________________________ApplicationsLocal 5V-to-3.3V DC-DC Conversion
Microprocessor Daughterboards
Power Supplies up to 10A or More
____________________________Features>90% Efficiency700µA Quiescent Supply Current120µA Standby Supply Current4.5V-to-5.5V Input RangeLow-Cost Application CircuitAll N-Channel SwitchesSmall External ComponentsTiny Shrink-Small-Outline Package (SSOP)Predesigned Applications:
Standard 5V to 3.3V DC-DC Converters up to 10A
High-Accuracy Pentium P54C VR-Spec SupplyFixed Output Voltages Available:
3.3V (Standard)
3.45V (High-Speed Pentium™)
3.6V (PowerPC™)
______________Ordering Information
MAX767, Synchronous, Step-Down
Power-Supply Controller
__________________Pin Configuration
________Typical Application CircuitPentium is a trademark of Intel.PowerPC is a trademark of IBM.
Ordering Information continued at end of data sheet.Contact factory for dice specifications.
MAX767
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
ABSOLUTE MAXIMUM RATINGSStresses 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.
VCCto GND.................................................................-0.3V, +7V
PGND to GND........................................................................±2V
BST to GND...............................................................-0.3V, +15V
LX to BST.....................................................................-7V, +0.3V
Inputs/Outputs to GND
(ON, REF, SYNC, CS, FB, SS).....................-0.3V, VCC+ 0.3V
DL toPGND.....................................................-0.3V, VCC+ 0.3V
DH to LX...........................................................-0.3V, BST + 0.3V
REF Short to GND.......................................................Momentary
REF Current.........................................................................20mA
Continuous Power Dissipation (TA= +70°C)
20-Pin SSOP (derate 8.00mW/°C above +70°C)..........640mW
Operating Temperature Ranges:
MAX767CAP/MAX767_CAP.................................0°C to +70°C
MAX767EAP/MAX767_EAP..............................-40°C to +85°C
Lead Temperature (soldering, 10sec).............................+300°C
ELECTRICAL CHARACTERISTICS(VCC= ON = 5V, GND = PGND = SYNC = 0V, IREF= 0mA, TA= TMINto TMAX, unless otherwise noted. Typical values are at TA= +25°C.)
MAX767
5V-to-3.3V, Synchronous, Step-Down
Power-Supply ControllerEFFICIENCY vs. OUTPUT CURRENT
(1.5A CIRCUIT)
MAX767-01
OUTPUT CURRENT (A)
EFFICIENCY (%)70
EFFICIENCY vs. OUTPUT CURRENT
(3A CIRCUIT)
MAX767-02
OUTPUT CURRENT (A)
EFFICIENCY (%)70
EFFICIENCY vs. OUTPUT CURRENT
(5A CIRCUIT)
MAX767-03
OUTPUT CURRENT (A)
EFFICIENCY (%)70
EFFICIENCY vs. OUTPUT CURRENT
(7A CIRCUIT)
MAX767-04
OUTPUT CURRENT (A)
EFFICIENCY (%)70
EFFICIENCY vs. OUTPUT CURRENT
(10A CIRCUIT)
MAX767-05
OUTPUT CURRENT (A)
EFFICIENCY (%)70
SWITCHING FREQUENCY vs.
PERCENT OF FULL LOAD
MAX767-06
LOAD CURRENT (% FULL LOAD)
SWITCHING FREQUENCY (kHz)
__________________________________________Typical Operating Characteristics
(Circuit of Figure 1 (5A configuration), VIN= 5V, oscillator frequency = 300kHz, TA= +25°C, unless otherwise noted.)
MAX767
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
____________________________Typical Operating Characteristics (continued)(Circuit of Figure 1 (5A configuration), VIN= 5V, oscillator frequency = 300kHz, TA= +25°C, unless otherwise noted.)
MAX767
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
______________________________________________________________Pin Description
MAX767
_____Standard Application CircuitsThis data sheet shows five predesigned circuits with
output current capabilities from 1.5A to 10A. Many
users will find one of these standard circuits appropri-
ate for their needs. If a standard circuit is used, the
remainder of this data sheet (Detailed Descriptionand
Applications Information and Design Procedure) can
be bypassed.
Figure 1 shows the Standard Application Circuit. Table 1
gives component values and part numbers for five dif-
ferent implementations of this circuit: 1.5A, 3A, 5A, 7A,
and 10A output currents.
Each of these circuits is designed to deliver the full
rated output load current over the temperature range
listed. In addition, each will withstand a short circuit of
several seconds duration from the output to ground. If
the circuit must withstand a continuous short circuit,
refer to the Short-Circuit Durationsection for the
required changes.
Layout and GroundingGood layout is necessary to achieve the designed out-
put power, high efficiency, and low noise. Good layout
includes the use of a ground plane, appropriate com-
ponent placement, and correct routing of traces using
appropriate trace widths. The following points are in
order of decreasing importance.A ground plane is essential for optimum perfor-
mance. In most applications, the circuit will be
located on a multilayer board and full use of the four
or more copper layers is recommended. Use the
top and bottom layers for interconnections and the
inner layers for an uninterrupted ground plane.Because the sense resistance values are similar to
a few centimeters of narrow traces on a printed cir-
cuit board, trace resistance can contribute signifi-
cant errors. To prevent this, Kelvin connect CS and
FB to the sense resistor; i.e., use separate traces
not carrying any of the inductor or load current, as
shown in Figure 2. These signals must be carefully
shielded from DH, DL, BST, and the LX node.
Important: place the sense resistor as close as pos-
sible to and no further than 10mm from the MAX767.Place the LX node components N1, N2, L1, and D2
as close together as possible. This reduces resis-
tive and switching losses and confines noise due to
ground inductance.The input filter capacitor C1 should be less than
10mm away from N1’s drain. The connecting cop-
per trace carries large currents and must be at least
2mm wide, preferably 5mm.Keep the gate connections to the MOSFETs short
for low inductance (less than 20mm long and more
than 0.5mm wide) to ensure clean switching.To achieve good shielding, it is best to keep all
switching signals (MOSFET gate drives DH and DL,
BST, and the LX node) on one side of the board
and all sensitive nodes (CS, FB, and REF) on the
other side.Connect the GND and PGND pins directly to the
ground plane, which should ideally be an inner
layer of a multilayer board.
_______________Detailed DescriptionNote: The remainder of this document contains the
detailed information necessary to design a circuit that
differs substantially from the five standard application
circuits. If you are using one of the predesigned stan-
dard circuits, the following sections are provided only
for your reading pleasure.
The MAX767 converts a 4.5V to 5.5V input to a 3.3V
output. Its load capability depends on external compo-
nents and can exceed 10A. The 3.3V output is generat-
ed by a current-mode, pulse-width-modulation (PWM)
step-down regulator. The PWM regulator operates at
either 200kHz or 300kHz, with a corresponding trade-
off between somewhat higher efficiency (200kHz) and
smaller external component size (300kHz). The
MAX767 also has a 3.3V, 5mA reference voltage. Fault-
protection circuitry shuts off the output should the refer-
ence lose regulation or the input voltage go below 4V
(nominally).
External components for the MAX767 include two N-
channel MOSFETs, a rectifier, and an LC output filter.
The gate-drive signal for the high-side MOSFET, which
must exceed the input voltage, is provided by a boost
circuit that uses a 0.1µF capacitor. The synchronous
rectifier keeps efficiency high by clamping the voltage
across the rectifier diode. An external low-value cur-
rent-sense resistor sets the maximum current limit, pre-
venting excessive inductor current during start-up or
under short-circuit conditions. An optional external
capacitor sets the programmable soft-start, reducing
in-rush surge currents upon start-up and providing
adjustable power-up time.
The PWM regulator is a direct-summing type, lacking a
traditional integrator-type error amplifier and the phase
shift associated with it. It therefore does not require
external feedback-compensation components, as long
as you follow the ESR guidelines in the Applications
Information and Design Proceduresections.
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
MAX767
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
Table 1. Component Values
Table 2. Component Suppliers
MAX767The main gain block is an open-loop comparator that
sums four signals: output voltage error signal, current-
sense signal, slope-compensation ramp, and the 3.3V
reference. This direct-summing method approaches
the ideal of cycle-by-cycle control of the output voltage.
Under heavy loads, the controller operates in full PWM
mode. Every pulse from the oscillator sets the output
latch and turns on the high-side switch for a period
determined by the duty factor (approximately
VOUT/ VIN).
As the high-side switch turns off, the synchronous recti-
fier latch is set; 60ns later, the low-side switch turns on.
The low-side switch stays on until the beginning of the
next clock cycle (in continuous-conduction mode) or
until the inductor current reaches zero (in discontinu-
ous-conduction mode). Under fault conditions where
the inductor current exceeds the 100mV current-limit
threshold, the high-side latch resets and the high-side
switch turns off.
At light loads, the inductor current fails to exceed the
25mV threshold set by the minimum-current compara-
tor. When this occurs, the PWM goes into Idle-Mode™,
skipping most of the oscillator pulses to reduce the
switching frequency and cut back switching losses.
The oscillator is effectively gated off at light loads
because the minimum-current comparator immediately
resets the high-side latch at the beginning of each
cycle, unless the FB signal falls below the reference
voltage level.
Soft-StartConnecting a capacitor from the soft-start pin (SS) to
ground allows a gradual build-up of the 3.3V output
after power is applied or ON is driven high. When ON is
low, the soft-start capacitor is discharged to GND.
When ON is driven high, a 4µA constant current source
charges the capacitor up to 4V. The resulting ramp volt-
age on SS linearly increases the current-limit compara-
tor set-point, increasing the duty cycle to the external
power MOSFETs. With no soft-start capacitor, the full
output current is available within 10µs (see Applications
Information and Design Proceduresection).
Synchronous RectifierSynchronous rectification allows for high efficiency by
reducing the losses associated with the Schottky rectifi-
er. Also, the synchronous-rectifier MOSFET is neces-
sary for correct operation of the MAX767’s boost gate-
drive supply.
When the external power MOSFET (N1) turns off, ener-
gy stored in the inductor causes its terminal voltage to
reverse instantly. Current flows in the loop formed by
the inductor (L1), Schottky diode (D2), and the load—
an action that charges up the output filter capacitor
(C2). The Schottky diode has a forward voltage of
about 0.5V which, although small, represents a signifi-
cant power loss and degrades efficiency. The synchro-
nous-rectifier MOSFET parallels the diode and is turned
on by DL shortly after the diode conducts. Since the
synchronous rectifier’s on resistance (rDS(ON)) is very
low, the losses are reduced. The synchronous-rectifier
MOSFET is turned off when the inductor current falls to
zero.
The MAX767’s internal break-before-make timing
ensures that shoot-through (both external switches
turned on at the same time) does not occur. The
Schottky rectifier conducts during the time that neither
MOSFET is on, which improves efficiency by preventing
the synchronous-rectifier MOSFET’s lossy body diode
from conducting.
The synchronous rectifier works under all operating
conditions, including discontinuous-conduction mode
and idle-mode.
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller™ Idle-Mode is a trademark of Maxim Integrated Products.
MAX767
5V-to-3.3V, Synchronous, Step-Down
Power-Supply ControllerFigure 3. MAX767 Block Diagram
MAX767
Gate-Driver Boost SupplyGate-drive voltage for the high-side N-channel switch is
generated with the flying-capacitor boost circuit shown
in Figure 4. The capacitor (C3) is alternately charged
from the 5V input via the diode (D1) and placed in par-
allel with the high-side MOSFET’s gate-source termi-
nals. On start-up, the synchronous rectifier (low-side)
MOSFET (N2) forces LX to 0V and charges the BST
capacitor to 5V. On the second half-cycle, the PWM
turns on the high-side MOSFET (N1); it does this by
closing an internal switch between BST and DH, which
connects the capacitor to the MOSFET gate. This pro-
vides the necessary enhancement voltage to turn on
the high-side switch, an action that “boosts” the 5V
gate-drive signal above the input voltage.
Ringing seen at the high-side MOSFET gates (DH) in
discontinuous-conduction mode (light loads) is a natur-
al operating condition. It is caused by the residual
energy in the tank circuit, formed by the inductor and
stray capacitance at the LX node. The gate-driver neg-
ative rail is referred to LX, so any ringing there is direct-
ly coupled to the gate-drive supply.
Modes of Operation
PWM ModeUnder heavy loads—over approximately 25% of full
load—the supply operates as a continuous-current
PWM supply (see Typical Operating Characteristics).
The duty cycle, %ON, is approximately:
VOUT%ON = ________
VIN
Current flows continuously in the inductor: first, it ramps
up when the power MOSFET conducts; second, it
ramps down during the flyback portion of each cycle as
energy is put into the inductor and then discharged into
the load. Note that the current flowing into the inductor
when it is being charged is also flowing into the load,
so the load is continuously receiving current from the
inductor. This minimizes output ripple and maximizes
inductor use, allowing very small physical and electrical
sizes. Output ripple is primarily a function of the filter
capacitor’s effective series resistance (ESR), and is
typically under 50mV (see Design Proceduresection).
Idle-ModeUnder light loads (<25% of full load), the MAX767
enhances efficiency by turning the drive voltage on and
off for only a single clock period, skipping most of the
clock pulses entirely. Asynchronous switching, seen as
“ghosting” on an oscilloscope, is thus a normal operat-
ing condition whenever the load current is less than
approximately 25% of full load.
At certain input voltage and load conditions, a transition
region exists where the controller can pass back and
forth from idle-mode to PWM mode. In this situation,
short pulse bursts occur, which make the current wave-
form look erratic but do not materially affect the output
ripple. Efficiency remains high.
Current LimitingThe voltage between CS and FB is continuously moni-
tored. An external, low-value shunt resistor is connect-
ed between these pins, in series with the inductor,
allowing the inductor current to be continuously mea-
sured throughout the switching cycle. Whenever this
voltage exceeds 100mV, the drive voltage to the exter-
nal high-side MOSFET is cut off. This protects the MOS-
FET, the load, and the input supply in case of short cir-
cuits or temporary load surges. The current-limiting
resistance is typically 20mΩfor 3A.
5V-to-3.3V, Synchronous, Step-Down
Power-Supply Controller
