MAX8524 MAXIM [Maxim Integrated Products], MAX8524 Datasheet - Page 12

• Manufacturer Part Number: MAX8524
• Description: 2- to 8-Phase VRM 10/9.1 PWM Controllers with Precise Current Sharing and Fast Voltage Positioning
• Manufacturer: MAXIM [Maxim Integrated Products]

The clock frequency of the MAX8524/MAX8525 is set
by an external resistor from OSC to ground. After
selecting the switching frequency per phase, f
the number of phases, using Table 3, select the clock
frequency. For 6- or 8-phase operation, connect an
external resistor to OSC of both master and slave con-
trollers even if the MAX8524/MAX8525 is operated in
2- to 8-Phase VRM 10/9.1 PWM Controllers
with Precise Current Sharing and Fast Voltage
Positioning
Table 2. VID Programmed Output
Voltage (VRM 9.1)
12
VID4
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
1
______________________________________________________________________________________
VID3
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
0
0
0
0
0
0
0
0
1
1
1
1
1
1
1
1
VID2
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
0
0
0
0
1
1
1
1
Clock Frequency (OSC)
VID1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
0
0
1
1
VID0
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
Shutdown
V
1.850
1.825
1.800
1.775
1.750
1.725
1.700
1.675
1.650
1.625
1.600
1.575
1.550
1.525
1.500
1.475
1.450
1.425
1.400
1.375
1.350
1.325
1.300
1.275
1.250
1.225
1.200
1.175
1.150
1.125
1.100
OUT
SW
, and
slave mode. A 1% resistor is recommended for the
R
should be placed as close as possible to the OSC pin.
A precision 2V reference is provided by the
MAX8524/MAX8525 at the REF pin. REF is capable of
sourcing up to 500µA for external loads. REF stays
alive when EN is low and while V
Connect a 0.22µF ceramic capacitor from REF to GND.
The capacitor should be placed as close to the REF pin
as possible.
An internal REFOK monitors the reference voltage. The
reference voltage must be above the REFOK threshold
of 1.85V to activate the controller. The controller is dis-
abled if the reference voltage falls below 1.81V.
The output current of each phase is sensed differential-
ly with a shared common return for each phase pair. A
low offset voltage and high-gain (50V/V) differential cur-
rent amplifier at each phase allow low-resistance cur-
rent-sense resistors to be used to minimize power
dissipation. Sensing the current at the output of each
phase offers advantages, including less noise sensitivi-
ty, more accurate current sharing between phases, and
the flexibility of using either a current-sense resistor or
the DC resistance of the output inductor.
Using the DC resistance, R
allows higher efficiency. In this configuration, the initial
tolerance and temperature coefficient of R
accounted for in the output-voltage droop-error budget.
An RC filtering network is needed to extract the current
information from the output inductor, as shown in Figure
1. The time constant of the RC network is governed by
equation 1:
Table 3. Clock Frequency Setting vs.
Switching Frequency and Number of
Phases
NO. OF PHASES
OSC
to maintain good frequency accuracy, and R
2
3
4
6
8
Output Current Sensing (CS_+, CS_-)
PWM2 = PWM4 = V
PWM4 = V
—
PWM4 = V
—
PIN CONNECTIONS
RC
Voltage Reference (REF)
=
R
DC
L
CC
CC
DC
, of the output inductor
CC
CC
is above UVLO.
DC
(
Eq
4 x f
3 x f
4 x f
3 x f
4 x f
f
CLKO
must be
) 1
SW
SW
SW
SW
SW
OSC