MAX1887 Maxim Integrated Products, MAX1887 Datasheet - Page 11

• Manufacturer Part Number: MAX1887
• Description: (MAX1887 / MAX1897) Quick-PWM Slave Controllers
• Manufacturer: Maxim Integrated Products

Table 1. Component Selection for Standard
Applications
Output Voltage
Input Voltage Range
Maximum Load Current
Inductor (each phase)
Frequency
High-Side MOSFET
(N
Low-Side MOSFET
(N
Input Capacitor (C
Output Capacitor (C
Current-Sense Resistors
(R
Voltage Positioning Gain
(A
MAX1887
H
L
CS
VPS
, each phase)
, each phase)
12
13
14
15
16
and R
)
COMPONENT
CM
PIN
)
MAX1897
IN
______________________________________________________________________________________
14
15
16
17
18
OUT
)
)
NAME
Panasonic ETQP6F0R6BFA
Sumida CDEP134H-0R6 or
LIMIT
Panasonic EEFUE0E271R
Fairchild (3) FDS7764A or
BST
DH
CIRCUIT OF FIGURE 1
TDK C4532X5R1E106M
V+
LX
300kHz (TON = float)
International Rectifier
International Rectifier
TMK432BJ106KM or
(2) IRF7822 or
(2) IRF7811W
0.6V to 1.75V
(6) 10µF 25V
(8) 270µF 2V
Taiyo Yuden
Quick-PWM Slave Controllers for
7V to 24V
Multiphase, Step-Down Supplies
1.5mΩ
0.6µH
40A
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).
Op en- D r ai n C ur r ent- Li m i t Outp ut. C onnect to the m aster contr ol l er ’ s ad j ustab l e cur r ent-
l i m i t i np ut ( ILIM ) accor d i ng to the S tand ar d Ap p l i cati on C i r cui t ( Fi g ur e 1) . When the
vol tag e acr oss the m aster contr ol l er ’ s cur r ent- sense r esi stor ( V
cur r ent- l i m i t thr eshol d ( V
2
ILI M
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.
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 (V
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
/10) , the M AX 1887/M AX 1897 p ul l s LIM IT l ow .
DESCRIPTION
Pin Description (continued)
On-Time Control and Active
Detailed Description
C M +
Current Balancing
- V
C M -
) exceed s the
COMP
11
).