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PDF MAX1864 Data sheet ( Hoja de datos )
| Número de pieza | MAX1864 | |
| Descripción | xDSL/Cable Modem Triple/Quintuple Output Power Supplies | |
| Fabricantes | Maxim Integrated | |
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19-2030; Rev 0; 4/01
EVAALVUAAILTAIOBNLEKIT
xDSL/Cable Modem Triple/Quintuple Output
Power Supplies
General Description
The MAX1864/MAX1865 power-supply controllers are
designed to address cost-conscious applications 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 MAX1864 generates three positive outputs, and the
MAX1865 generates four positive outputs and one neg-
ative output to provide a cost-effective system power
supply.
The MAX1864 includes a current-mode synchronous
step-down controller and two positive regulator gain
blocks. The MAX1865 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 0.8 ✕ VIN with an external resistive-
divider. The 100kHz/200kHz operating frequency
allows the use of low-cost aluminum-electrolytic capaci-
tors and low-cost power magnetics. Additionally, the
MAX1864/MAX1865 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 current-sense resistors.
The MAX1864/MAX1865 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 MAX1865’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. Additionally, the MAX1864/
MAX1865 feature soft-start for the step-down converter
and all the positive linear regulators, and have a power-
good output that monitors all of the output voltages.
Applications
xDSL, Cable, and ISDN Modems
Set-Top Boxes
Wireless Local Loop
Features
♦ 4.5V to 28V Input Voltage Range
♦ Master DC-DC Step-Down Converter
Preset 3.3V or Adjustable (1.236V to 0.8 ✕ VIN)
Output Voltage
Fixed-Frequency (100kHz/200kHz) PWM
Controller
No Current-Sense Resistor
Adjustable Current Limit
95% Efficient
♦ Two (MAX1864)/Four (MAX1865) Analog
Gain Blocks
Positive Analog Blocks Drive Low-Cost PNP
Pass Transistors to Build Positive Linear
Regulators
Negative Analog Block (MAX1865) Drives a
Low-Cost NPN Pass Transistor to Build a
Negative Linear Regulator
♦ Power-Good Indicator
♦ Soft-Start Ramp for All Positive Regulators
Ordering Information
PART
MAX1864TEEE
MAX1864UEEE
MAX1865TEEP
MAX1865UEEP
TEMP.
RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-
PACKAGE
16 QSOP
16 QSOP
20 QSOP
20 QSOP
fOSC
(kHz)
200
100
200
100
Pin Configurations
TOP VIEW
POK 1
COMP 2
OUT 3
FB 4
B2 5
FB2 6
B3 7
FB3 8
MAX1864
16 IN
15 VL
14 BST
13 DH
12 LX
11 DL
10 GND
9 ILIM
16 QSOP
Pin Configurations continued at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1 page  
xDSL/Cable Modem Triple/Quintuple Output
Power Supplies
ELECTRICAL CHARACTERISTICS (continued)
(VIN = 12V, ILIM = FB = GND, VBST - VLX = 5V, TA = -40°C to +85°C, unless otherwise noted.) (Note 4)
PARAMETER
POWER GOOD (POK)
OUT Trip Level (Preset Mode)
SYMBOL
CONDITIONS
MIN
FB = GND, falling edge, 1% hysteresis (typ) 2.85
FB Trip Level
(Adjustable Mode)
Falling edge, 1% hysteresis (typ)
1.058
FB2, FB3, FB4 Trip Level
FB5 Trip Level
Falling edge, 1% hysteresis (typ)
Rising edge, 35mV hysteresis (typ)
1.058
325
MAX UNITS
3.15 V
1.17 V
1.17 V
675 mV
Note 1: Connect VL to IN for operation with VIN < 5V.
Note 2: See Output Voltage Selection section.
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.
Typical Operating Characteristics
(Circuit of Figure 1, VIN = 12V, VOUT = 3.3V, TA = +25°C, unless otherwise noted.)
EFFICIENCY vs. LOAD CURRENT
(PRESET MODE)
100
VIN = 6.5V
90
80
70
60
50
0.01
VIN = 8V
VIN = 12V
VIN = 18V
VIN = 24V
VOUT = 3.3V
0.1 1
LOAD CURRENT (A)
10
OUTPUT VOLTAGE vs. LOAD CURRENT
(PRESET MODE)
3.33
3.32
3.31
3.30
3.29
3.28
3.27
0
0.5 1.0 1.5 2.0 2.5 3.0
LOAD CURRENT (A)
EFFICIENCY vs. LOAD CURRENT
(ADJUSTABLE MODE)
100
VIN = 6.5V
90
80
70
60
50
0.01
VIN = 8V
VIN = 12V
VIN = 18V
VIN = 24V
VOUT = 5.0V
0.1 1
LOAD CURRENT (A)
10
_______________________________________________________________________________________ 5
5 Page 
xDSL/Cable Modem Triple/Quintuple Output
Power Supplies
D1
CENTRAL CMPSH-3
C1
1μF
C2
1μF
RPOK
100kΩ
IN BST
DH
VL LX
ILIM DL
MAX1864
OUT
POK GND
RDH
10Ω
CBST
0.1μF
RDL
10Ω
INPUT
9V TO 18V
CIN
470μF
NL, NH: INTERNATIONAL RECTIFIER
IRF7303
Q1: TIP30
Q2: 2N3905
NH
T1
1
NL
VOUT = 3.3V
1A
COUT
470μF
CBE2
FB 2200pF
RBE2 C3
RCOMP
47kΩ
CCOMP
COMP
B2
220Ω
R1
10kΩ
Q1
10μF
VOUT2 = 2.5V
300mA
T1
8.2nF
FB2
R2
10kΩ
C4
10μF
B3
FB3
Figure 1. Standard MAX1864 Application Circuit
CBE3
4700pF
RBE3
220Ω
R3
30kΩ
R4
10kΩ
D2
NIHON EP05Q03L
C6
10μF
C5
470μF
Q2
C7 VOUT3 = 5.0V
10μF 100mA
the voltage across the load. Under overload conditions,
when the inductor current exceeds the selected cur-
rent-limit (see the Setting the Current Limit section), 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 MAX1864/MAX1865 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.
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 Amplifier
The MAX1864/MAX1865s’ current-sense circuit ampli-
fies (AV = 5) 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 comparator’s
inverting input. The PWM comparator turns-off the high-
side MOSFET when VSUM exceeds the integrated feed-
back 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 accuracy and improve
stability.
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 25 Páginas | |
| PDF Descargar | [ Datasheet MAX1864.PDF ] | |
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