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PDF MAX1897 Data sheet ( Hoja de datos )
| Número de pieza | MAX1897 | |
| Descripción | Quick-PWM Slave Controllers | |
| Fabricantes | Maxim Integrated Products | |
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19-2188; Rev 1; 9/02
Quick-PWM Slave Controllers for
Multiphase, Step-Down Supplies
General Description
The MAX1887/MAX1897 step-down slave controllers are
intended for low-voltage, high-current, multiphase DC-to-
DC applications. The MAX1887/MAX1897 slave con-
trollers can be combined with any of Maxim’s
Quick-PWM™ step-down controllers to form a multiphase
DC-to-DC converter. Existing Quick-PWM controllers,
such as the MAX1718, function as the master controller,
providing accurate output voltage regulation, fast tran-
sient response, and fault protection features.
Synchronized to the master’s low-side gate driver, the
MAX1887/MAX1897 include the Quick-PWM constant on-
time controller, gate drivers for a synchronous rectifier,
active current balancing, and precision current-limit cir-
cuitry.
The MAX1887/MAX1897 provide the same high effi-
ciency, ultra-low duty factor capability, and excellent
transient response as other Quick-PWM controllers. The
MAX1887/MAX1897 differentially sense the inductor
currents of both the master and the slave across cur-
rent-sense resistors. These differential inputs and the
adjustable current-limit threshold derived from an exter-
nal reference allow the slave controller to accurately
balance the inductor currents and provide precise cur-
rent-limit protection. The MAX1887/MAX1897’s dual-
purpose current-limit input also allows the slave
controller to automatically enter a low-power standby
mode when the master controller shuts down.
The MAX1887 triggers on the rising edge of the mas-
ter’s low-side gate driver, which staggers the on-times
of both master and slave, providing out-of-phase oper-
ation that can reduce the input ripple current and con-
sequently the number of input capacitors. The
MAX1897 features a selectable trigger polarity, allowing
out-of-phase or simultaneous in-phase operation.
Applications
Notebook Computers
CPU Core Supply
Single-Stage (BATT to VCORE) Converters
Two-Stage (5V to VCORE) Converters
Servers/Desktop Computers
Telecom
Typical Operating Circuit appears at end of data sheet.
Quick-PWM is a registered trademark of Maxim Integrated
Products, Inc.
Features
o Quick-PWM Slave Controller
o Precise, Active Current Balance (±1.25mV )
o Accurate, Adjustable Current-Limit Threshold
o Optimized for Low-Output Voltages (≤2V)
o 4V to 28V Battery Input Range
o Fixed 300kHz (MAX1887) or Selectable
200kHz/300kHz/550kHz (MAX1897) Switching
Frequency
o Drive Large Synchronous-Rectifier MOSFETs
o 525µA (typ) ICC Supply Current
o 20µA Standby Supply Current
o <1µA Shutdown (MAX1897) Supply Current
o Small 16-Pin QSOP (MAX1887), Compact
20-Pin 5mm x 5mm QFN (MAX1897), or
20-Pin 5mm x 5mm Thin QFN (MAX1897)
Ordering Information
PART
TEMP RANGE
MAX1887EEE -40°C to +85°C
MAX1897EGP* -40°C to +85°C
MAX1897ETP -40°C to +85°C
*Contact factory for availability.
PIN-PACKAGE
16 QSOP
20 QFN 5mm ✕ 5mm
20 Thin QFN 5mm ✕ 5mm
Pin Configuration
TOP VIEW
20 19 18 17 16
CM+ 1
CM- 2
TON 3
CS- 4
CS+ 5
MAX1897
15 LX
14 DH
13 SHDN
12 VCC
11 VDD
6 7 8 9 10
THIN QFN 5mm x 5mm
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  
Quick-PWM Slave Controllers for
Multiphase, Step-Down Supplies
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V+ = 15V, VCC = VDD = 5V, VOUT = VCOMP = 1.2V, VCM+ = VCM- = VCS+ = VCS- = 1.2V, SHDN = VCC
(MAX1897), TA = -40°C to +85°C, unless otherwise noted.) (Note 5)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX UNITS
Shutdown Supply Current (VCC)
(MAX1897, Note 3)
Measured at VCC; SHDN = GND
5 µA
CURRENT SENSING
On-Time Adjustment Range
0.42 < VCOMP < 2.8V, VOUT ≥ 0.7V -40 +40 %
COMP Output Current
ICOMP Sink and source
30 µA
Current-Balance Offset
(VCM+ - VCM-) -
(VCS+ - VCS-), ICOMP = 0,
-100mV ≤ (VCM+ - VCM-)
≤ +100mV
MAX1887
MAX1897
-2.0
-2.0
+2.0
+2.0
mV
Current-Sense, Common-Mode
Range
CM+, CM-, CS+, CS-
-0.2
+2.0
V
Positive Current-Limit Threshold
Negative Current-Limit
Threshold
ILIM Standby Threshold Voltage
FAULT PROTECTION
VC_LIM
VCM+ - VCM- and
VCS+ - VCS-
VCS+ - VCS-
VILIM = 0.5V
VILIM = 1V
VILIM = 0.5V
VILIM = 1V
47.5
97.5
-80
-160
0.2
52.5
102.5
-70
-140
0.3
mV
mV
V
VCC/VDD Undervoltage Lockout
Threshold (Note 3)
Rising edge, hysteresis = 20mV, switching
disabled below this level
3.45
3.85 V
GATE DRIVERS
DH Gate-Driver On-Resistance
(Note 4)
DL Gate-Driver On-Resistance
(Note 4)
LOGIC
TRIG Logic Levels
TON Logic Levels (MAX1897)
RON(DH)
VBST - VLX forced to
5V
RON(DL)
High state (pullup)
Low state (pulldown)
MAX1887
MAX1897
MAX1887
MAX1897
MAX1887
MAX1897
VTRIG
VTON
350mV hysteresis
High
Low
Logic high (VCC; 200kHz operation)
Open (300kHz operation)
Logic low (GND; 550kHz operation)
3.0
VCC - 0.4
1.5
3.5
Ω
4.5
3.5
4.5
Ω
1.0
2.0
V
1.2
3.1 V
0.5
Note 1: On-time and off-time specifications are measured from 50% point to 50% point at the DH pin with LX = PGND, VBST = 5V, and a
500pF capacitor from DH to LX to simulate external MOSFET gate capacitance. Actual in-circuit times may be different due to
MOSFET switching speeds.
Note 2: The trigger delay time, tTRIG, is measured from the time the TRIG pin transitions to time when the DL pin goes low.
Note 3: The 20-pin MAX1897 has a separate analog PWM supply voltage input (VCC) and gate-driver supply input (VDD). For the 16-pin
MAX1887 device, the analog PWM supply voltage input and the gate-driver supply voltage input are internally connected and
named VDD.
Note 4: Production testing limitations due to package handling require relaxed maximum on-resistance specifications for the MAX1897’s
QFN package. The MAX1887 and MAX1897 contain the same die, and the QFN package imposes no additional resistance in-
circuit.
Note 5: Specifications to -40°C are guaranteed by design and not production tested.
_______________________________________________________________________________________ 5
5 Page 
PIN
MAX1887 MAX1897
12 14
13 15
14 16
15 17
16 18
Quick-PWM Slave Controllers for
Multiphase, Step-Down Supplies
NAME
DH
LX
BST
V+
LIMIT
Pin Description (continued)
DESCRIPTION
High-Side Gate-Driver Output. DH swings from LX to BST.
Inductor Connection. Connect LX to the switched side of the inductor. LX serves as
the lower supply rail for the DH high-side gate driver.
Boost Flying-Capacitor Connection. Connect to an external capacitor and diode
according to the Standard Application Circuit (Figure 1). An optional resistor in
series with BST allows DH pullup current to be adjusted.
Battery Voltage Sense Connection. Connect V+ to the input power source. V+ is
used only for PWM one-shot timing (see the On-Time Control and Active Current
Balancing section).
Open-Drain Current-Limit Output. Connect to the master controller’s adjustable current-
limit input (ILIM) according to the Standard Application Circuit (Figure 1). When the
voltage across the master controller’s current-sense resistor (VCM+ - VCM-) exceeds the
current-limit threshold (VILIM/10), the MAX1887/MAX1897 pulls LIMIT low.
Table 1. Component Selection for Standard
Applications
COMPONENT
Output Voltage
Input Voltage Range
Maximum Load Current
Inductor (each phase)
Frequency
High-Side MOSFET
(NH, each phase)
Low-Side MOSFET
(NL, each phase)
CIRCUIT OF FIGURE 1
0.6V to 1.75V
7V to 24V
40A
0.6µH
Sumida CDEP134H-0R6 or
Panasonic ETQP6F0R6BFA
300kHz (TON = float)
International Rectifier
(2) IRF7811W
International Rectifier
(2) IRF7822 or
Fairchild (3) FDS7764A or
Input Capacitor (CIN)
Output Capacitor (COUT)
Current-Sense Resistors
(RCS and RCM)
Voltage Positioning Gain
(AVPS)
(6) 10µF 25V
Taiyo Yuden
TMK432BJ106KM or
TDK C4532X5R1E106M
(8) 270µF 2V
Panasonic EEFUE0E271R
1.5mΩ
2
Detailed Description
The MAX1887/MAX1897 step-down slave controllers
are intended for low-voltage, high-current, multiphase
DC-to-DC applications. The MAX1887/MAX1897 slave
controllers can be combined with any of Maxim’s
Quick-PWM step-down controllers to form a multiphase
DC-to-DC converter. When compared to single-phase
operation, multiphase conversion lowers the peak
inductor current by distributing the load current
between parallel power paths. This simplifies compo-
nent selection, power distribution to the load, and ther-
mal layout. Existing Quick-PWM controllers, such as the
MAX1718, function as the master controller, providing
accurate output voltage regulation, fast transient
response, and multiple fault protection features.
Synchronized to the master’s low-side gate driver, the
MAX1887/MAX1897 include a constant on-time con-
troller, synchronous rectifier gate drive, active current
balancing, and precision current-limit circuitry.
On-Time Control and Active
Current Balancing
The MAX1887/MAX1897 slave controller uses a con-
stant on-time, voltage feed-forward architecture similar
to Maxim’s Quick-PWM controllers (Figure 2). The con-
trol algorithm is simple: the high-side switch on-time is
determined solely by a one-shot whose period is
inversely proportional to input voltage and directly pro-
portional to the compensation voltage (VCOMP).
Another one-shot sets a minimum off-time (130ns typi-
cal). The on-time one-shot is triggered when the follow-
ing conditions are satisfied: The slave detects a
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 30 Páginas | |
| PDF Descargar | [ Datasheet MAX1897.PDF ] | |
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