Datasheet

MAX8537/MAX8538/MAX8539
Detailed Description
The MAX8537/MAX8539 controllers provide a complete
power-management solution for both DDR and combin-
er supplies. The MAX8537 and MAX8539 are config-
ured for out-of-phase and in-phase DDR power-supply
operations, respectively. In addition to the dual-syn-
chronous buck controllers, they also contain an addi-
tional amplifier to generate a total of three outputs: the
main memory voltage (V
DDQ
), the tracking
sinking/sourcing termination voltage (V
TT
), and the ter-
mination reference voltage (V
TTR
). The MAX8538 is
configured as a dual out-of-phase controller for point-
of-load supplies. Each buck controller can source or
sink up to 25A of current, while the termination refer-
ence can supply up to 15mA output.
The MAX8537/MAX8539 have a 1% accurate refer-
ence. The first buck controller generates V
DDQ
using
external resistor-dividers. The second synchronous
buck controller and the amplifier generate 1/2 V
DDQ
voltage for V
TT
and V
TTR
. The V
TT
and V
TTR
voltages
are maintained within 1% of 1/2 V
DDQ
.
The MAX8537/MAX8538/MAX8539 use a constant-fre-
quency voltage-mode architecture with operating fre-
quencies of 200kHz to 1.4MHz to allow flexible design.
An internal high-bandwidth (25MHz) operational ampli-
fier is used as an error amplifier to regulate the output
voltage. This allows fast transient response, reducing
the number of output capacitors. Synchronous rectifica-
tion ensures high efficiency and balanced current
sourcing and sinking capability for V
TT
. An all-N-FET
design optimizes efficiency and cost. The two convert-
ers can be operated in-phase or out-of-phase to mini-
mize capacitance and optimize performance for all
V
IN
/V
OUT
combinations.
Both channels have independent enable and power-
good functions. They also have high-side current-sense
architectures. ILIM pins allow the setting of an
adjustable, lossless current limit for different combina-
tions of load current and R
DS(ON)
. Additionally, accu-
rate overcurrent protection is achieved by using a
sensing resistor in series with the high-side FET. The
positive current-limit threshold is programmable
through an external resistor. Overvoltage protection is
achieved by latching off the high-side MOSFET and
latching on the low-side MOSFET when the output volt-
age exceeds 17% of its set output.
Dual-Synchronous Buck Controllers for Point-of-
Load, Tracking, and DDR Memory Power Supplies
8 _______________________________________________________________________________________
Pin Description (continued)
PIN
NAME
(MAX8537/
MAX8539)
NAME
(MAX8538)
FUNCTION
22 VL VL
Internal 5V Linear Regulator to Power the IC. VL is always on. Bypass with a ceramic
capacitor with 1µF/10mA of load current. The internal VL regulator can be disabled by
connecting VL and V+ to an externally generated 5V. VL output current can be
boosted with an external PNP transistor.
23 DL1 DL1 Low-Side Gate-Driver Output for Step-Down 1. Swings from PGND to VL.
24 PGND PGND Power Ground for Gate-Driver Circuits
25 ILIM1 ILIM1
Output Current-Limit Setting for Step-Down 1. Connect a resistor from ILIM1 to the
drain of the step-down 1 high-side MOSFET, or to the junction of the source of the
high-side MOSFET and the current-sense resistor to set the current-limit threshold.
See the Current-Limit Setting section.
26 LX1 LX1
External Inductor Input for Step-Down 1. Connect to the switched side of the inductor.
LX1 serves as the lower supply-voltage rail for the DH1 high-side gate driver and
current-limit circuitry.
27 DH1 DH1 High-Side Gate-Driver Step-Down 1. Swings from LX1 to BST1.
28 BST1 BST1
Bootstrap Input to Power Internal High-Side Driver for Step-Down 1. Connect to an
external capacitor and diode according to Figure 1.