MAX1964TEEE ,Tracking/Sequencing Triple/Quintuple Power-Supply Controllersapplications Master DC-DC Step-Down Converter:demanding voltage sequencing/tracking, such asPreset ..
MAX1964TEEE ,Tracking/Sequencing Triple/Quintuple Power-Supply ControllersApplicationsFB 4 MAX1964 13 DH FB 4 17 DHMAX1965B2 5 12 LX B2 5 16 LXxDSL, Cable, and ISDN ModemsFB ..
MAX1966ESA ,Low-Cost Voltage-Mode PWM Step-Down ControllersMAX1966/MAX196719-2286; Rev 1; 9/03Low-Cost Voltage-Mode PWMStep-Down Controllers
MAX1967EUB ,PLASTIC ENCAPSULATED DEVICESELECTRICAL CHARACTERISTICS(VIN = VL = VCC = 5V (MAX1967), VIN = 5V (MAX1966), T = -40°C to +85°C (N ..
MAX1967EUB ,PLASTIC ENCAPSULATED DEVICESFeaturesThe MAX1966/MAX1967 are voltage-mode pulse-width- Cost-Optimized Designmodulated (PWM), st ..
MAX1967EUB ,PLASTIC ENCAPSULATED DEVICESapplications.RequiredThey drive low-cost N-MOSFETs for both the high-sideswitch and synchronous rec ..
MAX491EESD+ ,±15kV ESD-Protected, Slew-Rate-Limited, Low-Power, RS-485/RS-422 TransceiversApplications:ceivers on the bus. The MAX488E–MAX491E areMAX3483E/MAX3485E/MAX3486E/MAX3488E/designe ..
MAX491EESD+T ,±15kV ESD-Protected, Slew-Rate-Limited, Low-Power, RS-485/RS-422 TransceiversApplicationsPART TEMP RANGE PIN-PACKAGELow-Power RS-485 TransceiversMAX481ECPA 0°C to +70°C 8 Plast ..
MAX491EPD ,Low-Power / Slew-Rate-Limited RS-485/RS-422 TransceiversMAX481/MAX483/MAX485/MAX487–MAX491/MAX148719-0122; Rev 5; 2/96Low-Power, Slew-Rate-LimitedRS-485/RS ..
MAX491EPD ,Low-Power / Slew-Rate-Limited RS-485/RS-422 TransceiversApplicationsMAX481C/D 0°C to +70°C Dice*Industrial-Control Local Area NetworksOrdering Information ..
MAX491EPD+ ,±15kV ESD-Protected, Slew-Rate-Limited, Low-Power, RS-485/RS-422 TransceiversApplications:ate from a single +5V supply.MAX3293/MAX3294/MAX3295: 20Mbps, +3.3V,Drivers are short- ..
MAX491ESD ,Low-Power / Slew-Rate-Limited RS-485/RS-422 TransceiversFeaturesThe MAX481, MAX483, MAX485, MAX487–MAX491, and' In µMAX Package: Smallest 8-Pin SOMAX1487 a ..
MAX1964TEEE
Tracking/Sequencing Triple/Quintuple Power-Supply Controllers
General DescriptionThe MAX1964/MAX1965 power-supply controllers are
designed to address cost-sensitive applications
demanding voltage sequencing/tracking, such as
cable modem consumer premise equipment (CPE),
xDSL CPE, and set-top boxes. Operating off a low-cost,
unregulated DC supply (such as a wall adapter output),
the MAX1964 generates three positive outputs and the
MAX1965 generates four positive outputs and one neg-
ative output to provide an inexpensive system power
supply.
The MAX1964 includes a current-mode synchronous
step-down controller and two positive regulator gain
blocks. The MAX1965 has one additional positive gain
block and one negative regulator gain block. The main
synchronous step-down controller generates a high-
current output that is preset to 3.3V or adjustable from
1.236V to 0.75 ✕VINwith an external resistive-divider.
The 200kHz operating frequency allows the use of low-
cost aluminum-electrolytic capacitors and low-cost
power magnetics. Additionally, the MAX1964/MAX1965
step-down controllers sense the voltage across the low-
side MOSFET’s on-resistance to efficiently provide the
current-limit signal, eliminating the need for costly cur-
rent-sense resistors.
The MAX1964/MAX1965 generate additional supply
rails at low cost. The positive regulator gain blocks use
an external PNP pass transistor to generate low voltage
rails directly from the main step-down converter (such
as 2.5V or 1.8V from the main 3.3V output) or higher
voltages using coupled windings from the step-down
converter (such as 5V, 12V, or 15V). The MAX1965’s
negative gain block uses an external NPN pass transis-
tor in conjunction with a coupled winding to generate
-5V, -12V, or -15V.
All output voltages are externally adjustable, providing
maximum flexibility. During startup, the MAX1964 fea-
tures voltage sequencing and the MAX1965 features
voltage tracking. Both controllers provide a power-
good output that monitors all of the output voltages.
ApplicationsxDSL, Cable, and ISDN Modems
Set-Top Boxes
Wireless Local Loop
Features4.5V to 28V Input Voltage RangeMaster DC-DC Step-Down Converter:
Preset 3.3V or Adjustable (1.236V to 0.75 x VIN)
Output Voltage
Fixed Frequency (200kHz) PWM Controller
No Current-Sense Resistor
Adjustable Current Limit
95% Efficient
Soft-StartTwo (MAX1964)/Four (MAX1965) Analog Gain
Blocks:
Positive Analog Blocks Drive Low-Cost PNP
Pass Transistors to Build Positive Linear
Regulators
Negative Analog Block (MAX1965) Drives a
Low-Cost NPN Pass Transistor to Build a
Negative Linear RegulatorPower-Good IndicatorVoltage Sequencing (MAX1964) or Tracking
(MAX1965)
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply Controllers
Pin Configurations19-2084; Rev 0; 7/01
Typical Operating Circuit appears at end of data sheet.
Ordering Information
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply Controllers
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.
IN, B2, B3, B4 to GND............................................-0.3V to +30V
B5 to OUT...............................................................-20V to +0.3V
VL, POK, FB, FB2, FB3, FB4, FB5 to GND...............-0.3V to +6V
LX to BST..................................................................-6V to +0.3V
BST to GND............................................................-0.3V to +36V
DH to LX....................................................-0.3V to (VBST+ 0.3V)
DL, OUT, COMP, ILIM to GND......................-0.3V to (VL+ 0.3V)
VL Output Current...............................................................50mA
VL Short Circuit to GND..................................................≤100ms
Continuous Power Dissipation (TA= +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)...........666mW
20-Pin QSOP (derate 9.1mW/°C above +70°C)...........727mW
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
ELECTRICAL CHARACTERISTICS
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply Controllers
ELECTRICAL CHARACTERISTICS(VIN= 12V, ILIM = FB = GND, VBST- VLX= 5V, TA
= 0°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.)
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply Controllers
ELECTRICAL CHARACTERISTICS
ELECTRICAL CHARACTERISTICS (continued)(VIN= 12V, ILIM = FB = GND, VBST- VLX= 5V, TA
= 0°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.)
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply Controllers
Note 1:Connect VL to IN for operation with VIN< 5V.
Note 2:See Output Voltage Selectionsection.
Note 3:The internal 5V linear regulator (VL) powers the thermal shutdown block. Shorting VL to GND disables thermal shutdown.
Note 4:Specifications to -40°C are guaranteed by design, not production tested.
ELECTRICAL CHARACTERISTICS (continued)(VIN= 12V, ILIM = FB = GND, VBST- VLX= 5V, TA
= -40°C to +85°C, unless otherwise noted.) (Note 4)
Typical Operating Characteristics(Circuit of Figure 1, VIN= 12V, VOUT= 3.3V, TA= +25°C, unless otherwise noted.)
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply Controllers
Typical Operating Characteristics (continued)(Circuit of Figure 1, VIN= 12V, VOUT= 3.3V, TA= +25°C, unless otherwise noted.)
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply ControllersPOSITIVE LINEAR REGULATOR
OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
(QLDO = 2N3905)
MAX1964/65 toc13
SUPPLY VOLTAGE (V)
OUTPUT VOLTAGE (V)
POSITIVE LINEAR REGULATOR
POWER-SUPPLY REJECTION RATIO
(QLDO = 2N3905)
MAX1964/65 toc14
FREQUENCY (kHz)
PSRR (dB)
POSITIVE LINEAR REGULATOR
LOAD TRANSIENT
(QLDO = 2N3905)MAX1964/65 toc15
100mA
2.457V
2.467V
A. IOUTZ = 1mA TO 100mA, 50mA/div
B. VOUTZ = 2.5V, 5mV/div
CLDO(POS) = 10µF CERAMIC, VSUP(POS) = 3.3V
CIRCUIT OF FIGURE 1
10µs/div
Typical Operating Characteristics (continued)(Circuit of Figure 1, VIN= 12V, VOUT= 3.3V, TA= +25°C, unless otherwise noted.)
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply Controllers
Typical Operating Characteristics (continued)(Circuit of Figure 1, VIN= 12V, VOUT= 3.3V, TA= +25°C, unless otherwise noted.)
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply ControllersNEGATIVE LINEAR REGULATOR
OUTPUT VOLTAGE vs. SUPPLY VOLTAGE
(QLDO = TIP29)
MAX1964/65 toc22
SUPPLY VOLTAGE (V)
OUTPUT VOLTAGE (V)
Typical Operating Characteristics (continued)(Circuit of Figure 1, VIN= 12V, VOUT- 3.3V, TA= +25°C, unless otherwise noted.)
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply Controllers
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply Controllers
Detailed DescriptionThe MAX1964/MAX1965 power-supply controllers pro-
vide system power for cable and xDSL modems. The
main step-down DC-DC controller operates in a cur-
rent-mode pulse-width-modulation (PWM) control
scheme to ease compensation requirements and pro-
vide excellent load and line transient response.
The MAX1964 includes two analog gain blocks to regu-
late two additional positive auxiliary output voltages,
and the MAX1965 includes four analog gain blocks to
regulate three additional positive and one negative aux-
iliary output voltages. The positive regulator gain blocks
can be used to generate low voltage rails directly from
the main step-down converter or higher voltages using
MAX1964/MAX1965negative gain block can be used in conjunction with a
coupled winding to generate -5V, -12V, or -15V.
DC-DC ControllerThe MAX1964/MAX1965 step-down converters use a
pulse-width-modulated (PWM) current-mode control
scheme (Figure 2). An internal transconductance ampli-
fier establishes an integrated error voltage at the COMP
pin. The heart of the current-mode PWM controller is an
open-loop comparator that compares the integrated
voltage-feedback signal against the amplified current-
sense signal plus the slope compensation ramp. At
each rising edge of the internal clock, the high-side
MOSFET turns on until the PWM comparator trips or the
maximum duty cycle is reached. During this on-time,
current ramps up through the inductor, sourcing current
to the output and storing energy in a magnetic field.
The current-mode feedback system regulates the peak
inductor current as a function of the output voltage error
signal. Since the average inductor current is nearly the
same as the peak inductor current (assuming that the
inductor value is relatively high to minimize ripple cur-
rent), the circuit acts as a switch-mode transconduc-
tance amplifier. It pushes the output LC filter pole,
normally found in a voltage-mode PWM, to a higher fre-
quency. To preserve inner-loop stability and eliminate
inductor stair casing, a slope-compensation ramp is
summed into the main PWM comparator.
During the second-half of the cycle, the high-side MOS-
FET turns off and the low-side N-Channel MOSFET
turns on. Now the inductor releases the stored energy
as its current ramps down, providing current to the out-
put. Therefore, the output capacitor stores charge when
the inductor current exceeds the load current, and dis-
charges when the inductor current is lower, smoothing
the voltage across the load. Under overload conditions
when the inductor current exceeds the selected cur-
rent-limit (see the Current Limitsection), the high-side
MOSFET is not turned on at the rising edge of the clock
and the low-side MOSFET remains on to let the inductor
current ramp down.
The MAX1964/MAX1965 operate in a forced-PWM
mode, so even under light loads, the controller main-
tains a constant switching frequency to minimize cross-
regulation errors in applications that use a transformer.
So the low-side gate-drive waveform is the complement
of the high-side gate-drive waveform, which causes the
inductor current to reverse under light loads.
Current-Sense AmplifierThe one MAX1964/MAX1965’s one current-sense circuit
amplifies (AV= 4.9) the current-sense voltage
generated by the high-side MOSFET’s on resistance
(RDS(ON)✕IINDUCTOR). This amplified current-sense
signal and the internal slope compensation signal are
summed together (VSUM) and fed into the PWM com-
parator’s inverting input. The PWM comparator turns off
the high-side MOSFET when the VSUMexceeds the
integrated feedback voltage (VCOMP). Place the high-
side MOSFET no further than 5mm from the controller
and connect IN and LX to the MOSFET using Kelvin
sense connections to guarantee current-sense accura-
cy and improve stability.
Current-Limit CircuitThe current-limit circuit employs a unique “valley” cur-
rent-limiting algorithm that uses the low-side MOSFET’s
on-resistance as a sensing element (Figure 3). If the
voltage across the low-side MOSFET (RDS(ON)✕
IINDUCTOR) exceeds the current-limit threshold at the
beginning of a new oscillator cycle, the MAX1964/
MAX1965 will not turn on the high-side MOSFET. The
actual peak current is greater than the current-limit
threshold by an amount equal to the inductor ripple cur-
rent. Therefore, the exact current-limit characteristic
and maximum load capability are a function of the low-
side MOSFET on-resistance, inductor value, input volt-
age, and output voltage. The reward for this uncertainty
is robust, lossless overcurrent limiting.
In adjustable mode, the current-limit threshold voltage is
approximately one-fifth the voltage seen at ILIM (IVALLEY
= 0.2 ✕VILIM). Adjust the current-limit threshold by con-
necting a resistive-divider from VL to ILIM to GND. The
current-limit threshold can be set from 106mV to
530mV, which corresponds to ILIM input voltages of
500mV to 2.5V. This adjustable current limit accommo-
dates MOSFETs with a wide range of on-resistance
characteristics (see the Design Proceduresection). The
current-limit threshold defaults to 250mV when ILIM is
connected to VL. The logic threshold for switchover to
the 250mV default value is approximately VL - 1V.
Carefully observe the PC board layout guidelines to
ensure that noise and DC errors don’t corrupt the cur-
rent-sense signals seen by LX and GND. The IC must
be mounted close to the low-side MOSFET with short
(less than 5mm), direct traces making a Kelvin sense
connection.
Synchronous Rectifier Driver (DL)Synchronous rectification reduces conduction losses in
the rectifier by replacing the normal Schottky catch
diode with a low-resistance MOSFET switch. The
MAX1964/MAX1965 also use the synchronous rectifier
to ensure proper startup of the boost gate-driver circuit
and to provide the current-limit signal.
racking/Sequencing Triple/Quintuple
Power-Supply Controllers
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply Controllers
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply Controllers
The DL low-side drive waveform is always the comple-
ment of the DH high-side drive waveform (with con-
trolled dead time to prevent cross-conduction or
“shoot-through”). A dead-time circuit monitors the DL
output and prevents the high-side FET from turning on
until DL is fully off. In order for the dead-time circuit to
work properly, there must be a low-resistance, low-
inductance path from the DL driver to the MOSFET
gate. Otherwise, the sense circuitry in the MAX1964/
MAX1965 will interpret the MOSFET gate as “off” when
gate charge actually remains. Use very short, wide
traces (50mils to 100mils wide if the MOSFET is 1 inch
from the device). The dead time at the other edge (DH
turning off) is determined by a fixed internal delay.
High-Side Gate-Drive Supply (BST)Gate-drive voltage for the high-side N-channel switch is
generated by a flying-capacitor boost circuit (Figure 1).
The capacitor between BST and LX is alternately
charged from the VL supply and placed parallel to the
high-side MOSFET’s gate and source terminals.
On startup, the synchronous rectifier (low-side MOS-
FET) forces LX to ground and charges the boost
capacitor to 5V. On the second half-cycle, the switch-
mode power supply turns on the high-side MOSFET by
closing an internal switch between BST and DH. This
provides the necessary gate-to-source voltage to turn
on the high-side switch, an action that boosts the 5V
gate-drive signal above the input voltage.
Internal 5V Linear Regulator (VL)All MAX1964/MAX1965 functions, except the current-
sense amplifier, are internally powered from the on-
chip, low-dropout 5V regulator. The maximum regulator
input voltage (VIN) is 28V. Bypass the regulator’s output
(VL) with a ceramic capacitor of at least 1µF to GND.
The VIN-to-VL dropout voltage is typically 200mV, so
when VINis less than 5.2V, VL is typically VIN- 200mV.
The internal linear regulator can source up to 20mA to
supply the IC, power the low-side gate driver, charge
the external boost capacitor, and supply small external
loads. When driving particularly large FETs, little or no
regulator current may be available for external loads.
For example, when switched at 200kHz, a large FET
with 40nC total gate charge requires 40nC x 200kHz, or
8mA.
Undervoltage LockoutIf VL drops below 3.5V, the MAX1964/MAX1965
assumes that the supply voltage is too low to make
valid decisions, so the undervoltage lockout (UVLO)
circuitry inhibits switching, forces POK low, and forces
the DL and DH gate drivers low. After VL rises above
3.5V, the controller powers up the outputs (see Startup
section).
Startup Externally, the MAX1964/MAX1965 start switching when
VL rises above the 3.5V undervoltage lockout thresh-
old. However, the controller is not enabled unless all
fourconditions are met: 1) VL exceeds the 3.5V under-
voltage lockout threshold, 2) the internal reference
exceeds 92% of its nominal value (VREF> 1.145V), 3)
the internal bias circuitry powers up, and 4) the thermal
limit is not exceeded. Once the MAX1964/MAX1965
assert the internal enable signal, the step-down con-
troller starts switching and enables soft-start.
The soft-start circuitry gradually ramps up to the refer-
ence voltage in order to control the rate of rise of the
MAX1964/MAX1965racking/Sequencing Triple/Quintuple
Power-Supply Controllers
