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.
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) I
CC
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)
Features
MAX1887/MAX1897
Ordering Information
PART
MAX1887EEE
MAX1897E
GP*
MAX1897ETP
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
16 QSOP
20 QFN 5mm
✕
5mm
20 Thin QFN 5mm
✕
5mm
*Contact
factory for availability.
Pin Configuration
TRIG
LIMIT
ILIM
V+
17
TOP VIEW
Applications
Notebook Computers
CPU Core Supply
Single-Stage (BATT to V
CORE
) Converters
Two-Stage (5V to V
CORE
) Converters
Servers/Desktop Computers
Telecom
CM+
CM-
TON
CS-
CS+
1
2
3
4
5
20
19
18
16
15
14
LX
DH
SHDN
V
CC
V
DD
BST
13
12
11
10
DL
MAX1897
6
COMP
7
POL
8
GND
9
PGND
Typical Operating Circuit appears at end of data sheet.
Quick-PWM is a registered trademark of Maxim Integrated
Products, Inc.
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.
Quick-PWM Slave Controllers for
Multiphase, Step-Down Supplies
MAX1887/MAX1897
ABSOLUTE MAXIMUM RATINGS
V+ to GND ..............................................................-0.3V to +30V
V
CC
, V
DD
to GND (Note 3) .......................................-0.3V to +6V
PGND to GND.....................................................................±0.3V
TRIG, LIMIT to GND .................................................-0.3V to +6V
SHDN
to GND (MAX1897)........................................-0.3V to +6V
ILIM, CM+, CM-, CS+, CS-, COMP
to GND....................................................-0.3V to (V
CC
+ 0.3V)
TON, POL to GND (MAX1897) ...................-0.3V to (V
CC
+ 0.3V)
DL to PGND................................................-0.3V to (V
DD
+ 0.3V)
BST to GND ............................................................-0.3V to +36V
DH to LX ....................................................-0.3V to (V
BST
+ 0.3V)
LX to BST..................................................................-6V to +0.3V
Continuous Power Dissipation (T
A
= +70°C)
16-Pin QSOP (derate 8.3mW/°C above +70°C)...........667mW
20-Pin 5mm x 5mm QFN (derate 20.0mW/°C
above +70°C)..............................................................1.60W
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
Stresses 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.
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V+ = 15V, V
CC
= V
DD
= 5V, V
OUT
= V
COMP
= 1.2V, V
CM+
= V
CM-
= V
CS+
= V
CS-
= 1.2V,
SHDN
= V
CC
(MAX1897),
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
PWM CONTROLLER
Input Voltage Range
Battery voltage, V+
V
CC
, V
DD
MAX1887 (300kHz), V+ = 12V, V
COMP
= 1.2V
TON = GND
MAX1897,
V+ = 12V,
V
COMP
= 1.2V
TON = open
TON = V
CC
4.0
4.5
320
171
320
464
355
190
355
515
75
Measured at V+; V
ILIM
> 0.35V
Measured at V
DD
; V
ILIM
> 0.35V
MAX1887
MAX1897
25
525
<1
525
<1
20
<1
20
<1
<1
<1
40
800
5
800
5
40
5
40
5
5
5
28.0
5.5
390
209
390
566
ns
µA
µA
µA
µA
µA
µA
µA
µA
µA
ns
V
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
On-Time (Note 1)
t
ON
Trigger Delay (Note 2)
SUPPLY CURRENTS
Quiescent Supply Current (V+)
Quiescent Supply Current (V
DD
)
(Note 3)
Quiescent Supply Current (V
CC
)
(MAX1897, Note 3)
Standby Supply Current (V+)
Standby Supply Current (V
DD
)
(Note 3)
Standby Supply Current (V
CC
)
(MAX1897, Note 3)
Shutdown Supply Current (V+)
(MAX1897)
Shutdown Supply Current (V
DD
)
(MAX1897, Note 3)
Shutdown Supply Current (V
CC
)
(MAX1897, Note 3)
t
TRIG
I+
I
DD
I
CC
Measured at V
CC
; V
ILIM
> 0.35V
Measured at V+; ILIM = GND
Measured at V
DD
; ILIM
= GND
MAX1887
MAX1897
Measured at V
CC
; ILIM = GND
Measured at V+; V
CC
= V
DD
= 0 or 5V,
SHDN
= GND
Measured at V
DD
;
SHDN
= GND
Measured at V
CC
;
SHDN
= GND
2
_______________________________________________________________________________________
Quick-PWM Slave Controllers for
Multiphase, Step-Down Supplies
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V+ = 15V, V
CC
= V
DD
= 5V, V
OUT
= V
COMP
= 1.2V, V
CM+
= V
CM-
= V
CS+
= V
CS-
= 1.2V,
SHDN
= V
CC
(MAX1897),
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
CURRENT SENSING
On-Time Adjustment Range
COMP Output Current
I
COMP
0.42 < V
COMP
< 2.8V, V
OUT
≥
0.7V
Sink and source
(V
CM+
- V
CM-
) -
(V
CS+
- V
CS-
), I
COMP
=
0, -100mV
≤
(V
CM+
-
V
CM-
)
≤
+100mV
MAX1887
MAX1897
-40
30
-1.25
-1.25
1.2
-0.2
-1
V
ILIM
= 0.5V
V
ILIM
= 1V
V
ILIM
= 0.5V
V
ILIM
= 1V
47.5
97.5
-80
-160
0.2
-100
t
LIMIT
V
OL(LIMIT)
I
LIMIT
Falling edge, 3mV over trip threshold
I
SINK
= 1mA
LIMIT forced to 5.5V
Rising edge, hysteresis = 20mV, switching
disabled below this level
Rising, hysteresis = 15°C (typ)
MAX1887
MAX1897
MAX1887
MAX1897
MAX1887
MAX1897
< 0.01
1.5
0.1
1.00
50.0
100.0
-75
-150
+2.0
+1
52.5
102.5
-70
-140
0.3
+100
+1.25
mV
+1.25
mS
V
µA
mV
mV
V
nA
µs
V
µA
+40
%
µA
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
MAX1887/MAX1897
Current-Balance Offset
Current-Balance
Transconductance
Current-Sense, Common-Mode
Range
Current-Sense Input Current
Positive Current-Limit Threshold
Negative Current-Limit
Threshold
ILIM Standby Threshold Voltage
ILIM Input Current
LIMIT Propagation Delay
LIMIT Output Low Voltage
LIMIT Leakage Current
FAULT PROTECTION
V
CC
/V
DD
Undervoltage Lockout
Threshold (Note 3)
Thermal Shutdown Threshold
GATE DRIVERS
DH Gate-Driver On-Resistance
(Note 4)
R
ON(DH)
V
C_LIM
(V
CM+
- V
CM-
) - (V
CS+
- V
CS-
) = ±25mV
CM+, CM-, CS+, CS-
CM+, CM-, CS+, CS-
V
CM+
- V
CM-
and
V
CS+
- V
CS-
V
CS+
- V
CS-
3.45
160
1.0
1.0
1.0
1.0
0.4
0.4
1.3
4.0
1.3
35
26
3.85
V
°C
V
BST
- V
LX
forced to 5V
High state (pullup)
3.5
4.5
3.5
4.5
1.0
2.0
Ω
DL Gate-Driver On-Resistance
(Note 4)
R
ON(DL)
Low state (pulldown)
Ω
DH Gate-Driver Source/Sink
Current
DL Gate-Driver Sink Current
DL Gate-Driver Source Current
Dead Time
I
DH
I
DL
I
DL
DH forced to 2.5V, V
BST
- V
LX
forced to 5V
DL forced to 2.5V
DL forced to 2.5V
DL rising
DH rising
A
A
A
ns
_______________________________________________________________________________________
3
Quick-PWM Slave Controllers for
Multiphase, Step-Down Supplies
MAX1887/MAX1897
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V+ = 15V, V
CC
= V
DD
= 5V, V
OUT
= V
COMP
= 1.2V, V
CM+
= V
CM-
= V
CS+
= V
CS-
= 1.2V,
SHDN
= V
CC
(MAX1897),
T
A
= 0°C to +85°C,
unless otherwise noted. Typical values are at T
A
= +25°C.)
PARAMETER
LOGIC
Logic Input High Voltage
(MAX1897)
Logic Input Low Voltage
(MAX1897)
TRIG Logic Levels
V
IH
V
IL
V
TRIG
SHDN,
POL; V
CC
= 4.5V to 5.5V
SHDN,
POL; V
CC
= 4.5V to 5.5V
350mV hysteresis
High
Low
V
CC
- 0.4
1.5
-1
-1
-2
-2
3.1
0.5
+1
+1
+1
+3
µA
V
3.0
1.2
2.4
0.8
V
V
V
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
Logic high (V
CC
; 200kHz operation)
TON Logic Levels (MAX1897)
V
TON
Open (300kHz operation)
Logic low (GND; 550kHz operation)
TRIG
Logic Input Current
SHDN
(MAX1897)
POL (MAX1897)
TON = GND or V
DD
(MAX1897)
ELECTRICAL CHARACTERISTICS
(Circuit of Figure 1, V+ = 15V, V
CC
= V
DD
= 5V, V
OUT
= V
COMP
= 1.2V, V
CM+
= V
CM-
= V
CS+
= V
CS-
= 1.2V,
SHDN
= V
CC
(MAX1897),
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 5)
PARAMETER
PWM CONTROLLER
MAX1887 (300kHz), V+ = 12V, V
COMP
= 1.2V
On Time (Note 3)
t
ON
MAX1897,
V+ = 12V,
V
COMP
= 1.2V
TON = GND (550kHz)
TON = open (300kHz)
TON = V
CC
(200kHz)
320
171
320
464
390
209
390
566
40
800
5
800
5
40
5
40
5
5
µA
µA
µA
µA
µA
µA
µA
µA
ns
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
SUPPLY CURRENTS
Quiescent Supply Current (V+)
Quiescent Supply Current (V
DD
)
(Note 3)
Quiescent Supply Current (V
CC
)
(MAX1897, Note 3)
Standby Supply Current (V+)
Standby Supply Current (V
DD
)
(Note 3)
Standby Supply Current (V
CC
)
(MAX1897, Note 3)
Shutdown Supply Current (V+)
(MAX1897)
Shutdown Supply Current (V
DD
)
(MAX1897, Note 3)
I+
I
DD
I
CC
Measured at V+; V
ILIM
> 0.35V
Measured at V
DD
;
V
ILIM
> 0.35V
MAX1887
MAX1897
Measured at V
CC
; V
ILIM
> 0.35V
Measured at V+; ILIM = GND
Measured at V
DD
;
ILIM = GND
MAX1887
MAX1897
Measured at V
CC
; ILIM = GND
Measured at V+; V
CC
= V
DD
= 0 or 5V,
SHDN
= GND
Measured at V
DD
;
SHDN
= GND
4
_______________________________________________________________________________________
Quick-PWM Slave Controllers for
Multiphase, Step-Down Supplies
ELECTRICAL CHARACTERISTICS (continued)
(Circuit of Figure 1, V+ = 15V, V
CC
= V
DD
= 5V, V
OUT
= V
COMP
= 1.2V, V
CM+
= V
CM-
= V
CS+
= V
CS-
= 1.2V,
SHDN
= V
CC
(MAX1897),
T
A
= -40°C to +85°C,
unless otherwise noted.) (Note 5)
PARAMETER
Shutdown Supply Current (V
CC
)
(MAX1897, Note 3)
CURRENT SENSING
On-Time Adjustment Range
COMP Output Current
I
COMP
0.42 < V
COMP
< 2.8V, V
OUT
≥
0.7V
Sink and source
(V
CM+
- V
CM-
) -
(V
CS+
- V
CS-
), I
COMP
= 0,
-100mV
≤
(V
CM+
- V
CM-
)
≤
+100mV
CM+, CM-, CS+, CS-
V
C_LIM
V
CM+
- V
CM-
and
V
CS+
- V
CS-
V
CS+
- V
CS-
V
ILIM
= 0.5V
V
ILIM
= 1V
V
ILIM
= 0.5V
V
ILIM
= 1V
MAX1887
MAX1897
-40
30
-2.0
-2.0
-0.2
47.5
97.5
-80
-160
0.2
Rising edge, hysteresis = 20mV, switching
disabled below this level
MAX1887
MAX1897
MAX1887
MAX1897
MAX1887
MAX1897
High
Low
V
CC
- 0.4
1.5
3.1
0.5
V
3.0
1.2
+2.0
mV
+2.0
+2.0
52.5
102.5
-70
-140
0.3
V
mV
mV
V
+40
%
µA
SYMBOL
CONDITIONS
Measured at V
CC
;
SHDN
= GND
MIN
TYP
MAX
5
UNITS
µA
MAX1887/MAX1897
Current-Balance Offset
Current-Sense, Common-Mode
Range
Positive Current-Limit Threshold
Negative Current-Limit
Threshold
ILIM Standby Threshold Voltage
FAULT PROTECTION
V
CC
/V
DD
Undervoltage Lockout
Threshold (Note 3)
GATE DRIVERS
DH Gate-Driver On-Resistance
(Note 4)
R
ON(DH)
3.45
3.85
V
V
BST
- V
LX
forced to
5V
High state (pullup)
3.5
4.5
3.5
4.5
1.0
2.0
Ω
DL Gate-Driver On-Resistance
(Note 4)
LOGIC
TRIG Logic Levels
R
ON(DL)
Low state (pulldown)
Ω
V
TRIG
350mV hysteresis
V
Logic high (V
CC
; 200kHz operation)
TON Logic Levels (MAX1897)
V
TON
Open (300kHz operation)
Logic low (GND; 550kHz operation)
Note 1:
On-time and off-time specifications are measured from 50% point to 50% point at the DH pin with LX = PGND, V
BST
= 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, t
TRIG
, 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 (V
CC
) and gate-driver supply input (V
DD
). For the 16-pin
MAX1887 device, the analog PWM supply voltage input and the gate-driver supply voltage input are internally connected and
named V
DD
.
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
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