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19-3201; Rev 0; 1/08
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Digital Power-Supply Controller/Monitor
with PMBus Interface
General Description
The MAX8688 is a fully integrated digital power-supply
controller and monitor IC that works with any existing
POL (point-of-load) power supply to provide complete
digital programmability. By interfacing to the reference
input, feedback node, and output enable, the MAX8688
takes control of the POL to provide functions such as
perfect tracking, sequencing, margining, and dynamic
adjustment of the output voltage.
The MAX8688 offers an accurate 12-bit analog-to-digi-
tal converter (ADC) accompanied with two differential
amplifiers for accurately monitoring both voltage and
current. An integrated 12-bit digital-to-analog converter
(DAC) is also available to margin power supplies as
well as dynamically adjust the output voltage with 0.2%
accuracy over temperature using this closed-loop sys-
tem. An internal temperature sensor provides an addi-
tional level of system monitoring.
The user-programmable registers provide flexible and
accurate control of time events such as a delay time
and transition period, monitoring for overvoltage and
undervoltage, overcurrent, reverse-current, overtemper-
ature fault and warning handling. The closed-loop oper-
ation is also programmable to make sure the MAX8688
works with any existing POL to provide superior regula-
tion accuracy and accurate margining.
The MAX8688 operates using a PMBus™-compliant
communication protocol. The device is programmed
using this protocol or simply with the use of a free
graphic-user interface (GUI) available from the Maxim
website that significantly reduces development time.
Once the configuration is complete, the results can be
saved into an EEPROM or loaded onto the part through
the PMBus at power-up. This allows remote configura-
tion of any POL using the MAX8688, replacing expen-
sive recalls or field service. Module current sharing is
also supported, since accurate current measurement
and fine resolution voltage control are available. The
MAX8688 can be programmed with up to 127 distinct
addresses to support large systems. The MAX8688 is
offered in a space-saving, 24-pin, lead-free 4mm x
4mm TQFN package.
Applications
Telecom Networking
DC-DC Modules and POLs
Servers
High-Reliability Infrastructure Equipment
PMBus is a trademark of SMIF, Inc.
Features
o PMBus Interface for Programming, Monitoring,
Sequencing Up and Down, and Accurate Output-
Voltage Control
o Controls Output Voltage with 0.2% Accuracy for
Line, Load, and Temperature Variations
o Output Voltage, Output Current, and Temperature
Monitoring with Adjustable Monitor Rate
o Current Measurement with 2.6% Accuracy and
Temperature Compensation Option
o Programmable Soft-Start and Soft-Stop Ramp
Rates
o Controls Up to 26 Power Supplies with Hardwired
Address Pins and Up to 127 POLs with Software
Addressing
o Compatible with REFIN and FB Terminals of POL
Power Supplies
o Protection for POL Against Overvoltage,
Undervoltage, Overcurrent, Negative Current and
Overtemperature Faults with No Action, Latch and
Retry (Hiccup) Options
o Open-Drain FLT Signal for Fault Detection
o Master-Slave Clocking Option Eliminates External
Clock Requirement and Provides Accurate Timing
Reference
o External EEPROM Interface for Auto-Programming
on Power-Up
Ordering Information
PART
TEMP RANGE
PIN-
PACKAGE
PKG
CODE
MAX8688ALETG+ -40°C to +85°C 24 TQFN-EP* T2444-4
MAX8688AHETG+ -40°C to +85°C 24 TQFN-EP* T2444-4
MAX8688BLETG+ -40°C to +85°C 24 TQFN-EP* T2444-4
MAX8688BHETG+ -40°C to +85°C 24 TQFN-EP* T2444-4
+Denotes a lead-free package.
*EP = Exposed pad.
Selector Guide
PART
ACCURACY
(%)
ENOUT POWER-UP
DEFAULT STATE
MAX8688ALETG+
0.2
Low
MAX8688AHETG+
0.2
High
MAX8688BLETG+
0.4
Low
MAX8688BHETG+
0.4
High
Pin Configuration appears at end of data sheet.
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.

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Digital Power-Supply Controller/Monitor
with PMBus Interface
ABSOLUTE MAXIMUM RATINGS
AVDD, DVDD to AGND .........................................-0.3V to +4.5V
DGND to AGND ..................................................................±0.3V
RS+, RS-, ISN+, ISN- to AGND ................................-0.3V to +6V
RS_C, ISN_C, A1/SCLE, A2/SDAE,
A3/ONOFF to AGND ............................-0.3V to (AVDD + 0.3V)
DACOUT to AGND ..................................-0.3V to (AVDD + 0.3V)
REFO to AGND......................................................-0.3V to +4.5V
Continuous Power Dissipation (TA = +70°C)
24-Pin TQFN (derate 27.8mW/°C above +70°C)...........2222mW*
θJA .................................................................................36°C/W
θJC................................................................................2.7°C/W
SCL, SDA, CLKIO, RST to DGND .........................-0.3V to +4.5V
ENOUT, FLT to DGND..............................................-0.3V to +6V
Thermal Resistance from Junction to Exposed Pad ......2.7°C/W
Operating Temperature .......................................-40°C to +85°C
Junction Temperature ........................................................150°C
Storage Temperature.........................................-65°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°C
*As per JEDEC51 standard (multilayered board).
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
(AVDD = DVDD = 3.3V, TA = -40°C to +85°C, VRS+ - VRS- = 2V, VRS- = AGND, unless otherwise stated.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX UNITS
GENERAL
AVDD/DVDD Operating Range
3.0 3.6 V
AVDD and DVDD Operating
Supply Current
AVDD UVLO
OUTPUT-VOLTAGE SENSING
VRS+ = VRS- = VISN+ = VISN- = AGND
Rising
Hysteresis
6.7 8.5
2.70 2.8 2.95
100
mA
V
mV
MAX8688A, TA = 0°C to +85°C, -0.2 +0.2
VRS+ = 1V, VRS- = 0V
Voltage Regulation Accuracy (2V
Range, Table 8) (Note 2)
MAX8688A, TA = -40°C to +85°C,
VRS+ = 1V, VRS- = 0V
MAX8688B, TA = 0°C to +85°C,
VRS+ = 1V, VRS- = 0V
-0.3
-0.4
+0.3
+0.4
%
MAX8688B, TA = -40°C to +85°C,
VRS+ = 1V, VRS- = 0V
-0.5
+0.5
MAX8688A, TA = 0°C to +85°C,
VRS+ = 2.5V, VRS- = 0V
-0.3
+0.3
Voltage Regulation Accuracy (5.5V
range, Table 8) (Note 2)
MAX8688A, TA = -40°C to +85°C,
VRS+ = 2.5V, VRS- = 0V
MAX8688B, TA = 0°C to +85°C,
VRS+ = 2.5V, VRS- = 0V
MAX8688B, TA = -40°C to +85°C,
VRS+ = 2.5V, VRS- = 0V
-0.4
-0.4
-0.5
+0.4
+0.4
+0.5
%
RS+, RS- Differential Mode Range
0 5.5 V
RS- to AGND Differential Voltage
RS+ Input Bias Current
RS- Input Bias Current
2V range, VRS+ = -0.25V to 2V
5.5V range, VRS+ = -0.25V to 5.5V
2V or 5.5V range, VRS- = -0.25V to +0.25V
-250
-10
-10
-10
+250
+15
+60
0
mV
µA
µA
2 _______________________________________________________________________________________

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Digital Power-Supply Controller/Monitor
with PMBus Interface
ELECTRICAL CHARACTERISTICS (continued)
(AVDD = DVDD = 3.3V, TA = -40°C to +85°C, VRS+ - VRS- = 2V, VRS- = AGND, unless otherwise stated.) (Note 1)
PARAMETER
OUTPUT CURRENT SENSE
SYMBOL
CONDITIONS
MIN TYP
Current-Sense Accuracy (Note 2)
ISN+, ISN- Common-Mode Range
ISN+, ISN- Common-Mode
Current-Sense Error
VISN+ = 1V, VISN+ - VISN- = 20mV,
TA = +25°C to +85°C
VISN+ = 1V, VISN+ - VISN- = 20mV,
TA = -40°C to +85°C
VCM = 0 to 5.5V, VDM = 20mV
-2.6
-7
0
0.9
ISN+, ISN- Differential Mode
Range
-10
ISN+, ISN- Input Bias Current
RS_C, ISN_C
RS_C, ISN_C Output Impedance
TEMPERATURE SENSING
Temperature Sensing Accuracy
CLKIO
CLKIO Input-Logic Low Voltage
CLKIO Input-Logic High Voltage
CLKIO Input Bias Current
CLKIO Input Clock Duty Cycle
CLKIO Output Low Voltage
CLKIO Output High Leakage
ISN+, ISN- to AGND = 0 or 5.5V
Exposed pad = -40°C to +100°C
CLKIO = 0 or 3.6V
fCLKIO = 100kHz to 2500kHz
CLKIO in output mode, ISINK = 4mA
CLKIO = DVDD = AVDD = 3.6V
-20
0.2
±3
2.1
-1
20
-1
CLKIO Input/Output Clock Rise
Time
Pullup = 560, CLOAD = 20pF
20
CLKIO Input/Output Clock Fall
Time
Pullup = 560, CLOAD = 20pF
2
MAX
+2.6
+7
5.5
+40
+40
0.8
+1
80
0.4
+1
UNITS
%
V
%
mV
µA
k
°C
V
V
µA
%
V
µA
ns
ns
CLKIO Pullup Voltage
DVDD
V
CLKIO Input Frequency
fEXT_CLK
CLKIO Output Frequency
Accuracy
ENOUT, FLT OPEN-DRAIN LOGIC OUTPUTS
ENOUT, FLT Output Low Voltage
ENOUT, FLT Output High Leakage
ENOUT, FLT Pullup Voltage
DAC
DAC Resolution
ISINK = 4mA
ENOUT = FLT = 5.5V,
DVDD = AVDD = 3.6V
DAC Output-Voltage Range
No load
100 2500 kHz
0.95 1.00 1.05 MHz
0.4
-1 +1
5.5
12
REFO -
1 LSB
V
µA
V
bits
V
_______________________________________________________________________________________ 3

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Digital Power-Supply Controller/Monitor
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ELECTRICAL CHARACTERISTICS (continued)
(AVDD = DVDD = 3.3V, TA = -40°C to +85°C, VRS+ - VRS- = 2V, VRS- = AGND, unless otherwise stated.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
DAC Output-Voltage Slew Rate
DAC Output Resistance
DAC Driving Capability
ADC
ADC Resolution
MAX8688A
MAX8688B
THREE-STATE ADDRESS PINS (A3/ONOFF, A2/SDAE, A1/SCLE)
Three-State Address Pins Input
Low Voltage
MIN TYP MAX
0.6
5
2
12
11
0.3
Three-State Address Pins Input
Low Threshold Hysteresis
50
Three-State Address Pins Input
High Voltage
AVDD -
0.4
Three-State Address Pins Input
High Threshold Hysteresis
50
Three-State Address Pins Input
Bias Current
AVDD = 3.6V, A3/ONOFF = A2/SDAE =
A1/SCLE = AVDD or AGND
-12
THREE-STATE ADDRESS PINS (A2/SDAE (DATA) AND A1/SCLE (CLOCK) WITH EEPROM) (Note 3)
A2/SDAE, A1/SCLE Output Low
Voltage
Output sink current = 100µA (Note 4)
+12
0.3 x
AVDD
A2/SDAE, A1/SCLE Output High
Voltage
Output source current = 100µA (Note 5)
THREE-STATE ADDRESS PIN (A3/ONOFF AS POL ON/OFF CONTROL)
Minimum A3/ONOFF Control Pulse
Low Time
tA3_LOW
0.7 x
AVDD
250
Minimum A3/ONOFF Control Pulse
High Time
SCL, SDA SMBus™ SIGNALS
Maximum SMBus Speed
SCL, SDA Input Low Voltage
SCL, SDA Input High Voltage
SCL, SDA Output Low Voltage
SCL, SDA Input Leakage Per
Device Pin
tA3_HIGH
VSMB_IL
VSMB_IH
VSMB_OL
DVDD = 3.0V to 3.6V
DVDD = 3.0V to 3.6V
DVDD = 3.0V to 3.6V at ISINK = 4mA
ISMB_ILEAK DVDD = 3.6V, SCL = SDA = 0 or 3.6V
750
100
0.8
2.1 DVDD
0.4
-1 +1
UNITS
V/µs
mA
Bits
V
mV
V
mV
µA
V
V
µs
µs
kHz
V
V
V
µA
SMBus is a trademark of Intel Corp.
4 _______________________________________________________________________________________

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Digital Power-Supply Controller/Monitor
with PMBus Interface
ELECTRICAL CHARACTERISTICS (continued)
(AVDD = DVDD = 3.3V, TA = -40°C to +85°C, VRS+ - VRS- = 2V, VRS- = AGND, unless otherwise stated.) (Note 1)
PARAMETER
RST INPUT
RST Input Low Voltage
RST Input High Voltage
RST Input Bias Current
Minimum SMBus Interface Reset
Pulse Width
SYMBOL
CONDITIONS
VRST_IL
VRST_IH
DVDD = 3.0V to 3.6V
DVDD = 3.0V to 3.6V
RST = DVDD or DGND
tSMB_RST
MIN TYP MAX UNITS
0.8 V
2.1 V
10 µA
1 455 µs
SMBus Interface Recovery Time
After Interface Reset
Minimum Reset Pulse Width
Recovery Time After Device Reset
OTHER TIMING PARAMETERS
PMBus Command Response Time
Fault Response Time
tSMB_WAIT
tRST
tRST_WAIT
tPMB_RSP
tFAULT_RSP
Overvoltage fault
Overcurrent fault
15
565
15
300
5
5
µs
µs
µs
µs
ms
Note 1: Production tested at TA = +25°C and TA = +85°C. Specifications from TA = -40°C to +25°C are guaranteed by design,
unless otherwise noted.
Note 2: Production tested at TA = +85°C only. All other temperatures are guaranteed by design.
Note 3: When an EEPROM is connected to A2/SDAE and A1/SCLE, these pins cannot be hardwired to ground or supply. They must
be connected through 33k±5% resistors.
Note 4: Equivalent of having 33kpulldown resistor to DGND.
Note 5: Equivalent of having 33kpullup resistor to DVDD.
(AVDD = DVDD = 3.3V, TA = +25°C, unless otherwise noted.)
REFIN MODE SOFT-START
WITH TRACKING
MAX8688 toc01
VOUT_4 = 1.8V
VOUT_3 = 1.5V
VOUT_2 = 1.2V
VOUT_1 = 1.0V
0.5V/div
Typical Operating Characteristics
VOUT_4 = 1.8V
VOUT_3 = 1.5V
VOUT_2 = 1.2V
VOUT_1 = 1.0V
REFIN MODE SOFT-STOP
WITH TRACKING
MAX8688 toc02
0.5V/div
2ms/div
2ms/div
_______________________________________________________________________________________ 5