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MAX6819UT+T-MAX6820UT-MAX6820UT+T
SOT23 Power-Supply Sequencers
General DescriptionThe MAX6819/MAX6820 are power-supply sequencers
for dual-voltage microprocessors (µPs) and multivoltage
systems. These devices monitor a primary supply voltage
and enable/disable an external n-channel MOSFET
switch for a secondary supply voltage. The MAX6819/
MAX6820 control local component voltage sequencing
when system power-on/power-off characteristics cannot
be guaranteed (supplies come from a multivoltage sys-
tem bus, silver box, or must be sequenced in different
modes for components on the same board). These small
power-supply sequencers improve system reliability.
The MAX6819/MAX6820 include an internal voltage ref-
erence/comparator with externally adjustable thresh-
olds to monitor the primary power supply. When the
primary supply is below the desired threshold, an exter-
nal secondary supply MOSFET switch is disabled.
When the primary supply exceeds the threshold, an
internal charge pump is activated and the external
MOSFET switch is enabled to connect the secondary
supply to the load. The charge pump fully enhances the
n-channel MOSFET switch to provide a very low RDS-voltage drop. The devices can be connected to
support various supply sequencing priorities such as
VI/Obefore VCOREor VCOREbefore VI/O.
The MAX6819 features a logic-driven EN input to
enable/disable the external MOSFET drive and includes
an internally fixed 200ms enable timeout period
(VPRIMARY GOODto VSECONDARY ENABLE). The
MAX6820 allows the enable timeout period to be
adjusted with a single external capacitor. Both devices
are specified over the automotive temperature range
(-40°C to +125°C) and are available in space-saving
6-pin SOT23 packages.
ApplicationsDual-Voltage Microprocessors
Multivoltage Systems
Digital Signal Processors
Power PC™ Series Processors
FeaturesAdjustable Primary Supply Voltage Monitor
(Monitors Down to 0.62V)Internal Charge Pump to Enhance External
Secondary Supply n-Channel MOSFET SwitchDelay from Primary Supply Good to Secondary
Supply Enabled
Factory Fixed 200ms (MAX6819)
Capacitor Adjustable (MAX6820)Logic Driven ENABLE Input (MAX6819)Immune to Short Voltage TransientsFew External Components-40°C to +125°C Operating Temperature Range Small 6-Pin SOT23 Package
MAX6819/MAX6820
SOT23 Power-Supply Sequencers19-1951; Rev 3; 12/05
Ordering InformationPART TEMP RANGE PIN-
PACKAGE TOPM ARK
MAX6819UT-T-40°C to +125°C6 SOT23-6AARF
MAX6820UT-T-40°C to +125°C6 SOT23-6AARG
Pin ConfigurationsGNDSETVVCC2GATE
VCC1
MAX6819
SOT23-6TOP VIEW
Products must be ordered in 2,500 piece increments.
Devices are available in both leaded and lead-free packaging.
Specify lead-free by replacing “-T” with “+T” when ordering.
Typical Operating CircuitsSETV
VCC2GATE
DUAL-SUPPLY
BOARD OR μP
PRIMARY SUPPLY
(3.3V)
SECONDARY SUPPLY
(1.8V)
VCC1GND
OFF
MAX6819
Pin Configurations and Typical Operating Circuits
continued at end of data sheet.Power PC is a trademark of IBM corp.
MAX6819/MAX6820
SOT23 Power-Supply Sequencers
ABSOLUTE MAXIMUM RATINGSStresses 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.
Note 1:100% production tested at TA= +25°C. Specifications over temperature limit are guaranteed by design.
Note 2:Either VCC1or VCC2must be > 2.125V. The other supply can go to 0.
Note 3:Guaranteed by design, not production tested.
Note 4:tDELAY(s) = 2.48 ✕106✕CSET
Referenced to GND
VCC1, VCC2, EN.....................................................-0.3V to +6.0V
SETV, SETD..................-0.3V to the higher of (VCC1+ 0.3V) and
(VCC2+ 0.3V)
GATE...................................................................-0.3V to +12.0V
Input Current/Output Current (all pins)...............................20mA
Continuous Power Dissipation (TA= +70°C)
6-Pin SOT23 (derate 8.7mW/°C above +70°C)............696mW
Operating Temperature Range.........................-40°C to +125°C
Junction Temperature......................................................+150°C
Storage Temperature Range.............................-65°C to +150°C
Lead Temperature (soldering 10s)..................................+300°C
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSOperating Voltage RangeV CC1,CC2(Note 2)0.95.5V
VCC1, VCC2 Supply CurrentICCVCC1 = VCC2 = +3.3V60120µAC C 1 , V C C 2 D i sab l e M od e C ur r entVCC1 = VCC2 = +3.3V, EN = GND20µA
MAX68196VCC1, VCC2 Slew Rate (Note 3)MAX6820 (Note 4)1.2 / tDELAYV/s
Undervoltage Lockout (UVLO)VUVLO1.8752.02.125V
SETV ThresholdVTHVSETV rising, enables GATE0.6020.6180.634V
SETV Input Current(Note 3)10100nA
SETV Threshold HysteresisVSETV falling, disables GATE-1%
SETV to GATE DelaytDELAYVSETV > VTH, VEN ≥ 2V (MAX6819)140200280ms
SETD Ramp Current (MAX6820)ISETDVCC1 or V CC2 > +2.125V400500600nA
SETD Voltage (MAX6820)VSETDVCC1 or VCC2 > +2.125V1.2101.2421.273V
SETD Threshold Hysteresis
(MAX6820)VSETD falling-62mV
GATE Turn-On TimetONC GATE = 1500p F, V C C 2 = + 3.3V , VGATE = + 7.8V 0.51.510ms
GATE Turn-Off TimetOFFC GATE = 1500p F, V C C 2 = + 3.3V , VGATE = + 0.5V 30µs
With respect to VCC2 (Note 2)
RGATE > 50MΩ to VCC24.55.56.0
GATE VoltageVGATE
With respect to VCC2 (Note 2)
RGATE > 5MΩ to VCC24.06.0
VIL0.4EN Input VoltageVIHVCC1 or VCC2 > +2.125V to + 5.5V2.0V
ELECTRICAL CHARACTERISTICS(VCC1or VCC2> +2.125V to +5.5V, TA= -40°C to +125°C, unless otherwise specified. Typical values are at TA= +25°C.) (Note 1)
MAX6819/MAX6820
SOT23 Power-Supply SequencerstDELAY vs. TEMPERATURE
MAX6819 toc01
TEMPERATURE (°C)
DELAY
(ms)
(MAX6819)
1ms/div
GATE TURN-ON TIMEVGATE
5V/div
MAX6819 toc02
CLOAD = 1500pF
20μs/div
GATE TURN-OFF TIMEVSETV
500mV/div
VGATE
5V/div
MAX6819 toc03
CLOAD = 1500pF2.01.50.51.02.53.03.54.04.55.0
VCC2 vs. GATE VOLTAGEMAX6819 toc04
VCC2 (V)
GATE
(V)VCC1 = +3.3V
VSETV = 1V2.01.50.51.02.53.03.54.04.55.0
VCC2 vs. GATE VOLTAGEMAX6819 toc05
VCC2 (V)
GATE
(V)
VCC1 = 0
VSETV = 1V2.01.50.51.02.53.03.54.04.55.0
VCC2 vs. GATE VOLTAGEMAX6819 toc06
VCC2 (V)
GATE
(V)
VCC1 = +3.3V
VSETV = VCC2
Typical Operating Characteristics(TA = +25°C, unless otherwise noted.)
MAX6819/MAX6820
SOT23 Power-Supply SequencersVSETV vs. TEMPERATURE
MAX6819 toc07
TEMPERATURE (°C)
SETV
(V)
SUPPLY CURRENT vs. TEMPERATURE
MAX6819 toc08
TEMPERATURE (°C)
SUPPLY CURRENT (
VEN = 2V
VSETV = 2V
VCC2 = +3.3V
VCC1 = +5V
VEN = 2V
VSETV = 2V
VCC1 = +3.3V
VCC2 = +5V
ICC2
ICC1
ICC2 vs. VCC2
MAX6819 toc09
VCC2 (V)
ICC2
VCC1 = 0
VEN = 2V
VSETV = 2V
ICC2 vs. VCC2
MAX6819 toc10
VCC2 (V)
ICC2
VCC1 = 3.3V
VEN = 2V
VSETV = 2V
Typical Operating Characteristics (continued)(TA = +25°C, unless otherwise noted.)
Detailed DescriptionMany dual-supply processors or multivoltage boards
require one power supply to rise to the proper operat-
ing voltage before another supply is applied. Improper
sequencing can lead to chip latchup, incorrect device
initiation, or long-term reliability degradation. If the vari-
ous supply voltages are not locally generated (coming
from a main system bus, an externally purchased silver
box, or a nonsequenced power management chip),
power-on and power-off sequencing can be difficult to
control or predict. Supply loading can affect turn-
on/turn-off times from board to board.
The MAX6819/MAX6820 provide proper local voltage
sequencing in multisupply systems. The sequencers use
an external n-channel MOSFET to switch the secondary
supply to the load only when the primary supply is above
a desired operating voltage threshold. The n-channel
MOSFET operates in a default off mode when the primary
supply is below the desired threshold or if neither supply
exceeds the sequencer’s UVLO level.
When the primary supply voltage is above the set
threshold, the external MOSFET is driven on. An inter-
nal charge pump fully enhances the external MOSFET
by providing a gate-to-source voltage (VGS) of +5.5V
(typ). The charge pump fully enhances the MOSFET to
yield a low drain-to-source impedance (RDS(ON)) for
reduced switch voltage drop. The MOSFET is never dri-
ven on unless the sequencer can provide a minimum
VGSenhancement, ensuring that the switch MOSFET
never operates in its higher impedance linear range.
Either supply may act as the primary source, regard-
less of the voltage level, provided that VCC1or VCC2is
greater than 2.125V (Figure 1 and Figure 2).
MAX6819/MAX6820
SOT23 Power-Supply Sequencers
PIN
MAX6819MAX6820
NAMEFUNCTIONVCC1Supply Voltage 1. Either VCC1 or VCC2 must be greater than the UVLO to enable
external MOSFET drive.GNDGroundSETVSequence Threshold Set. Connect to an external resistor-divider network to set the
VCC1 threshold that enables GATE turn-on. The internal reference is 0.618V.EN
Active-High Enable. GATE drive is enabled tDELAY after EN is driven high. GATE
drive is immediately disabled when EN is driven low. Connect to the higher of VCC1
and VCC2 if not used.SETDGATE Delay Set Input. Connect an external capacitor from SETD to GND to adjust
the delay from SETV > VTH to GATE turn-on. tDELAY (s) = 2.484 x 106 x CSET (F).GATE
GATE Drive Output. GATE drives an external n-channel MOSFET to connect VCC2 to
the load. GATE drive enables tDELAY after SETV exceeds VTH and ENABLE is driven
high. GATE drive is immediately disabled when SETV drops below VTH or ENABLE is
driven low. When enabled, an internal charge pump drives GATE to VCC2 + 5.5V to
fully enhance the external n-channel MOSFET.VCC2Supply Voltage 2. Either VCC1 or VCC2 must be greater than the UVLO to enable
external MOSFET drive.
Pin DescriptionSETV
( ) FOR MAX6820 ONLY
VCC2
VCC2 OUT
0.62V
VCC1
GND
SEQUENCE
DELAY/
LOGIC
GATE
EN (SETD)
GATE DRIVE
CHARGE PUMP
UVLO
Figure 1. Functional Diagram
