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PDF MAX1876 Data sheet ( Hoja de datos )
| Número de pieza | MAX1876 | |
| Descripción | Dual 180 Out-of-Phase PWM Step- Down Controllers with POR | |
| Fabricantes | Maxim Integrated | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de MAX1876 (archivo pdf) en la parte inferior de esta página. Total 21 Páginas | ||
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19-2431; Rev 0; 7/02
EVAALVUAAILTAIOBNLEKIT
Dual 180° Out-of-Phase PWM Step-
Down Controllers with POR
General Description
The MAX1875/MAX1876 dual, synchronized, step-down
controller generates two outputs from input supplies
ranging from 4.75V to 23V. Each output is adjustable from
sub-1V to 18V and supports loads of 10A or higher. Input
voltage ripple and total RMS input ripple current are
reduced by synchronized 180° out-of-phase operation.
The switching frequency is adjustable from 100kHz to
600kHz with an external resistor. Alternatively, the con-
troller can be synchronized to an external clock gener-
ated to another MAX1875/MAX1876 or a system clock.
One MAX1875/MAX1876 can be set to generate an in-
phase, or 90° out-of-phase, clock signal for synchro-
nization with additional controllers. This allows two
controllers to operate either as an interleaved two- or
four-phase system with each output shifted by 90°.
These devices also feature soft-start and soft-stop.
The MAX1875/MAX1876 eliminate the need for current-
sense resistors by utilizing the low-side MOSFET’s on-
resistance as a current-sense element. This protects
the DC-DC components from damage during output-
overload conditions or when output short-circuit faults
without requiring a current-sense resistor. Adjustable
foldback current limit reduces power dissipation during
short-circuit conditions. The MAX1876 includes a
power-on reset output to signal the system when both
outputs reach regulation.
The MAX1875/MAX1876 are available in a 24-pin QSOP
package. An evaluation kit is available to speed designs.
Applications
Network Power Supplies
Telecom Power Supplies
DSP, ASIC, and FPGA Power Supplies
Set-Top Boxes
Broadband Routers
Servers
Typical Operating Circuit appears at end of data sheet.
Features
o Two Independent Output Voltages
o 180° Out-of-Phase Operation
o 90° Out-of-Phase Operation
(Using Two MAX1875/MAX1876s)
o Foldback Current Limit
o 4.75V to 23V Input Supply Range
o 0 to 18V Output-Voltage Range (Up to 10A)
o >90% Efficiency
o Fixed-Frequency Pulse-Width Modulation (PWM)
Operation
o Adjustable 100kHz to 600kHz Switching
Frequency
o External SYNC Input
o Clock Output for Master/Slave Synchronization
o Soft-Start and Soft-Stop
o RST Output with 140ms Minimum Delay (MAX1876)
o Lossless Current Limit (No Sense Resistor)
Ordering Information
PART
MAX1875EEG
MAX1876EEG
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
24 QSOP
24 QSOP
Pin Configuration
TOP VIEW
COMP2 1
FB2 2
ILIM2 3
OSC 4
V+ 5
REF 6
GND 7
CKO 8
SYNC 9
ILIM1 10
FB1 11
COMP1 12
MAX1875/
MAX1876
QSOP
24 EN
23 DH2
22 LX2
21 BST2
20 DL2
19 VL
18 PGND
17 DL1
16 BST1
15 LX1
14 DH1
13 RST
(MAX1876 ONLY)
________________________________________________________________ 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  
Dual 180° Out-of-Phase PWM Step-
Down Controllers with POR
Typical Operating Characteristics (continued)
(Circuit of Figure 1, VIN = 12V, TA = +25°C, unless otherwise noted.)
SOFT-START AND SOFT-STOP WAVEFORM
MAX1875 toc07
5V
EN
0V
VOUT2
1V/div
0V
VOUT2
1V/div
0V
RESET TIMEOUT (MAX1876 ONLY)
MAX1875 toc08
5V/div
EN
0
VOUT2
0V
VOUT1
0V
VRST
0V
OUT-OF-PHASE WAVEFORM
MAX1875 toc09
VOUT1
20mV/div
12V
VLX1
0V
12V
VLX2
0V
VOUT2
20mV/div
1ms/div
100ms/div
1µs/div
EXTERNALLY SYNCHRONIZED
SWITCHING WAVEFORM
5VMAX1875 toc10
VSYNC
0V
5V
VCK0
0V
10V
VLX1
0V
VOUT1
10mV/div
AC-COUPLED
400ns/div
CKO OUTPUT WAVEFORM
MAX1875 toc11
SYNC = GND
400ns/div
5V
VCK0
0V
10V
VLX1
0V
VOUT1
10mV/div
AC-COUPLED
CKO OUTPUT WAVEFORM
MAX1875 toc12
SYNC = VL
5V
VCK0
0V
10V
VLX1
0V
VOUT1
10mV/div
400ns/div
SHORT-CIRCUIT CURRENT FOLDBACK
AND RECOVERY
MAX1875 toc13
IOUT1 = 10A(5A/div)
VOUT1 = 1.8V(1V/div)
SHORT
VOUT2
VOUT2 = 2.5V(1V/div)
IOUT2 = 10A(5A/div)
4ms/div
_______________________________________________________________________________________ 5
5 Page 
Dual 180° Out-of-Phase PWM Step-
Down Controllers with POR
VL
BST_
DH_
LX_
MAX1875
5Ω
INPUT
(VIN)
Figure 3. Reducing the Switching-Node Rise Time
On the rising edge of EN both controllers enter soft-
start. Soft-start gradually ramps up to the reference
voltage seen by the error amplifier in order to control
the outputs’ rate of rise and reduce input surge cur-
rents during startup. The soft-start period is 1024 clock
cycles (1024/fSW), and the internal soft-start DAC
ramps up the voltage in 64 steps. The output reaches
regulation when soft-start is completed. On the falling
edge of EN both controllers simultaneously enter soft-
stop, which reverses the soft-start ramp. The part
enters shutdown after soft-stop is complete.
Reset Output (MAX1876 Only)
RST is an open-drain output. RST pulls low when either
output falls below 90% of its nominal regulation voltage.
Once both outputs exceed 90% of their nominal regulation
voltages and both soft-start cycles are completed, RST
goes high impedance. To obtain a logic-voltage output,
connect a pullup resistor from RST to the logic supply volt-
age. A 100kΩ resistor works well for most applications. If
unused, leave RST grounded or unconnected.
Clock Synchronization (SYNC, CKO)
SYNC serves two functions: SYNC selects the clock
output (CKO) type used to synchronize slave con-
trollers, or it serves as a clock input so the
MAX1875/MAX1876 can be synchronized with an exter-
nal clock signal. This allows the MAX1875/MAX1876 to
funtion as either a master or slave. CKO provides a
clock signal synchronized to the MAX1875/MAX1876s’
switching frequency, allowing either in-phase (SYNC =
GND) or 90° out-of-phase (SYNC = VL) synchronization
of additional DC-DC controllers (Figure 5). The
MAX1875/MAX1876 support the following three operat-
ing modes:
• SYNC = GND: The CKO output frequency equals
REG1’s switching frequency (fCKO = fDH1) and the
CKO signal is in phase with REG1’s switching fre-
quency. This provides 2-phase operation when syn-
chronized with a second slave controller.
• SYNC = VL: The CKO output frequency equals two
times REG1’s switching frequency (fCKO = 2fDH1)
and the CKO signal is phase shifted by 90° with
respect to REG1’s switching frequency. This pro-
vides 4-phase operation when synchronized with a
second MAX1875/MAX1876 (slave controller).
• SYNC Driven by External Oscillator: The controller
generates the clock signal by dividing down the
SYNC input signal, so that the switching frequency
equals half the synchronization frequency (fSW =
fSYNC/2). REG1’s conversion cycles initiate on the ris-
ing edge of the internal clock signal. The CKO output
frequency and phase match REG1’s switching fre-
quency (fCKO = fDH1) and the CKO signal is in
phase. Note that the MAX1875/MAX1876 still require
ROSC when SYNC is externally clocked and the inter-
nal oscillator frequency should be set to 50% of the
synchronization frequency (fOSC = 0.5 fSYNC).
Thermal Overload Protection
Thermal overload protection limits total power dissipation
in the MAX1875/MAX1876. When the device’s die-junc-
tion temperature exceeds TJ = +160°C, an on-chip ther-
mal sensor shuts down the device, forcing DL_ and DH_
low, allowing the IC to cool. The thermal sensor turns the
part on again after the junction temperature cools by
10°C. During thermal shutdown, the regulators shut
down, RST goes low, and soft-start is reset. If the VL lin-
ear-regulator output is short-circuited, thermal-overload
protection is triggered.
Design Procedure
Effective Input Voltage Range
Although, the MAX1875/MAX1876 controllers can oper-
ate from input supplies ranging from 4.75V to 23V, the
input voltage range can be effectively limited by the
MAX1875/MAX1876s’ duty-cycle limitations. The maxi-
mum input voltage is limited by the minimum on-time
(tON(MIN)):
VIN(MAX) ≤
VOUT
tON(MIN)fSW
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 21 Páginas | |
| PDF Descargar | [ Datasheet MAX1876.PDF ] | |
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