General Description
The 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-
ON voltage drop. The devices can be connected to
support various supply sequencing priorities such as
VI/O before VCORE or VCORE before 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 GOOD to 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.
Applications
Dual-Voltage Microprocessors
Multivoltage Systems
Digital Signal Processors
Power PC™ Series Processors
Features
♦Adjustable Primary Supply Voltage Monitor
(Monitors Down to 0.62V)
♦Internal Charge Pump to Enhance External
Secondary Supply n-Channel MOSFET Switch
♦Delay from Primary Supply Good to Secondary
Supply Enabled
Factory Fixed 200ms (MAX6819)
Capacitor Adjustable (MAX6820)
♦Logic Driven ENABLE Input (MAX6819)
♦Immune to Short Voltage Transients
♦Few External Components
♦-40°C to +125°C Operating Temperature Range
♦Small 6-Pin SOT23 Package
MAX6819/MAX6820
SOT23 Power-Supply Sequencers
________________________________________________________________ Maxim Integrated Products 1
19-1951; Rev 3; 12/05
Ordering Information
PART
TEMP RANGE
PIN-
PACKAGE
TOP
M ARK
MAX6819UT-T
-40°C to +125°C 6 SOT23-6
AARF
MAX6820UT-T
-40°C to +125°C 6 SOT23-6
AARG
Pin Configurations
GND
ENSETV
16VCC2
5GATE
VCC1
MAX6819
SOT23-6
TOP VIEW
2
34
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 Circuits
ENSETV
VCC2 GATE
DUAL-SUPPLY
BOARD OR µP
PRIMARY SUPPLY
(3.3V)
SECONDARY SUPPLY
(1.8V)
VCC1 GND
ON
OFF
MAX6819
Pin Configurations and Typical Operating Circuits
continued at end of data sheet.
Power PC is a trademark of IBM corp.
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
MAX6819/MAX6820
SOT23 Power-Supply Sequencers
2_______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.
Note 1: 100% production tested at TA= +25°C. Specifications over temperature limit are guaranteed by design.
Note 2: Either VCC1 or VCC2 must 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
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX
UNITS
Operating Voltage Range V
CC1,
V
CC2 (Note 2) 0.9 5.5 V
VCC1, VCC2 Supply Current ICC VCC1 = VCC2 = +3.3V 60
120
µA
V
C C 1
, V
C C 2
D i sab l e M od e C ur r ent
VCC1 = VCC2 = +3.3V, EN = GND 20 µA
MAX6819 6
VCC1, VCC2 Slew Rate (Note 3) MAX6820 (Note 4)
1.2 / tDELAY
V/s
Undervoltage Lockout (UVLO)
VUVLO 1.875
2.0
2.125
V
SETV Threshold VTH VSETV rising, enables GATE
0.602 0.618 0.634
V
SETV Input Current (Note 3) 10
100
nA
SETV Threshold Hysteresis VSETV falling, disables GATE -1 %
SETV to GATE Delay
tDELAY
VSETV > VTH, VEN ≥ 2V (MAX6819)
140 200 280
ms
SETD Ramp Current (MAX6820)
ISETD VCC1 or V CC2 > +2.125V
400 500 600
nA
SETD Voltage (MAX6820)
VSETD
VCC1 or VCC2 > +2.125V
1.210 1.242 1.273
V
SETD Threshold Hysteresis
(MAX6820) VSETD falling -62 mV
GATE Turn-On Time tON
C
GATE
= 1500p F, V
C C 2 = + 3.3V , VGATE
= + 7.8V
0.5 1.5 10 ms
GATE Turn-Off Time tOFF
C
GATE
= 1500p F, V
C C 2 = + 3.3V , VGATE
= + 0.5V
30 µs
With respect to VCC2 (Note 2)
RGATE > 50MΩ to VCC2 4.5 5.5 6.0
GATE Voltage
VGATE
With respect to VCC2 (Note 2)
RGATE > 5MΩ to VCC2 4.0 6.0
V
VIL 0.4
EN Input Voltage VIH
VCC1 or VCC2 > +2.125V to + 5.5V 2.0 V
ELECTRICAL CHARACTERISTICS
(VCC1 or 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 Sequencers
_______________________________________________________________________________________ 3
1ms/div
GATE TURN-ON TIME
VGATE
5V/div
MAX6819 toc02
CLOAD = 1500pF
20µs/div
GATE TURN-OFF TIME
VSETV
500mV/div
VGATE
5V/div
MAX6819 toc03
CLOAD = 1500pF
0
6
4
2
8
10
12
0 2.01.50.5 1.0 2.5 3.0 3.5 4.0 4.5 5.0
VCC2 vs. GATE VOLTAGE
MAX6819 toc05
VCC2 (V)
VGATE (V)
VCC1 = 0
VSETV = 1V
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX6819/MAX6820
SOT23 Power-Supply Sequencers
4_______________________________________________________________________________________
100
104
102
108
106
112
110
114
-40 0 20-20 40 60 80 100 120
SUPPLY CURRENT vs. TEMPERATURE
MAX6819 toc08
TEMPERATURE (°C)
SUPPLY CURRENT (µA)
VEN = 2V
VSETV = 2V
VCC2 = +3.3V
VCC1 = +5V
VEN = 2V
VSETV = 2V
VCC1 = +3.3V
VCC2 = +5V
ICC2
ICC1
0
20
40
60
80
100
120
140
0213456
ICC2 vs. VCC2
MAX6819 toc10
VCC2 (V)
ICC2 (µA)
VCC1 = 3.3V
VEN = 2V
VSETV = 2V
Typical Operating Characteristics (continued)
(TA = +25°C, unless otherwise noted.)
Detailed Description
Many 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
VGS enhancement, 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 VCC1 or VCC2 is
greater than 2.125V (Figure 1 and Figure 2).
MAX6819/MAX6820
SOT23 Power-Supply Sequencers
_______________________________________________________________________________________ 5
PIN
MAX6819
MAX6820
NAME FUNCTION
11V
CC1 Supply Voltage 1. Either VCC1 or VCC2 must be greater than the UVLO to enable
external MOSFET drive.
22GND Ground
33SETV Sequence 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.
4—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.
—4SETD GATE 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).
55GATE
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.
66V
CC2 Supply Voltage 2. Either VCC1 or VCC2 must be greater than the UVLO to enable
external MOSFET drive.
Pin Description
SETV
( ) 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
MAX6819/MAX6820
Applications Information
Adjusting tDELAY
The MAX6820 features a capacitor adjustable
sequence delay. The adjustable delay provides power
sequencing for a wide range of devices with different
power-supply delay requirements. Connect a capacitor
(CSET) between SETD and GND to adjust the delay
time (Figure 2). Calculate the sequence delay time as
follows:
tDELAY (s) = 2.48 ✕106✕CSET
Setting Threshold Voltage at SETV
The threshold voltage is the minimum VCC1 voltage at
which VCC2 turn-on is acceptable. To monitor voltages
higher than the threshold voltage, connect external
resistors as a voltage-divider to SETV, and calculate the
minimum VCC turn-on voltage as follows:
R1 = R2 ((VTRIP / VTH) - 1)
where VTRIP is the minimum turn-on voltage at VCC1
and VTH = 0.618V (Figure 2).
Since SETV input current is 10nA (typ), high value resis-
tors can be used.
Selecting the Pass MOSFET
The external pass MOSFET is connected in series with
the sequenced power-supply source. Since the load
current and the MOSFET drain-to-source impedance
(RDS) determine the voltage drop, the on characteristics
of the MOSFET affect the load supply accuracy. The
MAX6819/MAX6820 fully enhance the external MOSFET
out of its linear range to ensure the lowest drain-to-
source on impedance. For highest supply accuracy/
lowest voltage drop, select a MOSFET with an appropri-
ate drain-to-source on impedance for a gate-to-source
bias of 4.5V to 6.0V.
Gate Drive Characteristics
The MAX6819/MAX6820 internal charge pump drives
the n-channel MOSFET with a gate-to-source voltage
(VGS) of 5.5V, ensuring low MOSFET on-resistance
RDS(ON). The charge pump drives the high-impedance
capacitive load of a MOSFET gate input.
Loading the GATE output resistively adds load current
and reduces gate drive capability. The internal charge
pump does not require external capacitors.
The external pass MOSFET is disabled, and charge
pump circuitry is turned off when neither VCC1 nor VCC2
are above the 1.875V UVLO or EN is low.
Logic Driven Supply Sequencing
The MAX6819 offers a logic-compatible enable input
(EN) that allows digital devices to control sequencing.
When the TTL/CMOS-compatible EN input is logic-low,
the GATE output is low. When the EN input is logic-high
(and SETV is above the monitor threshold), the GATE
output is enabled after an internally fixed 200ms delay.
For a logic-controlled sequencer when voltage monitor-
ing is not desired, connect SETV to VCC1 or VCC2 >
0.62V (Figure 3).
Sequencing Three or More Supplies
Cascade multiple MAX6819/MAX6820 to sequence
more than two supplies. Daisy-chaining devices allows
one sequencer to monitor the passed voltage of an
upstream sequencer through the SETV comparator
inputs. EN allows any sequencer to be shut down inde-
pendent of the SETV levels. Figure 4 shows an example
of a three-supply system in which the first supply must
come up before the second supply and the third supply
must yield for both supplies.
Negative-Going Voltage
Transient Immunity
The MAX6819/MAX6820 power-supply voltage sequen-
cers are relatively immune to short-duration (pulse
width), negative-going voltage transients (Figure 5).
However, the amplitude of the transient is inversely pro-
portional to its pulse width.
Chip Information
TRANSISTOR COUNT: 638
PROCESS: BiCMOS
SOT23 Power-Supply Sequencers
6_______________________________________________________________________________________
SETDSETV
CSET
VCC1
R1
R2
MAX6820
Figure 2. tDELAY (MAX6820 ONLY) and VTH Adjust
MAX6819/MAX6820
SOT23 Power-Supply Sequencers
_______________________________________________________________________________________ 7
SETD/ENSETV
VCC2 GATE
MULTISUPPLY
BOARD OR µP
5(V) PRIMARY VOLTAGE SUPPLY
3.3(V) SECONDARY VOLTAGE SUPPLY
1.8(V) THIRD VOLTAGE SUPPLY
VCC1 GND
R3
R4
R1
R2
SETD/ENSETV
VCC2 GATE
VCC1 GND
MAX6819
MAX6820
MAX6819
MAX6820
Figure 4. Sequencing Three Power Supplies
Figure 5. Maximum Transient Duration vs. SETV Threshold
in Overdrive
18
0
0.01 10.1
6
2
14
10
20
8
4
16
12
SETV THRESHOLD OVERDRIVE, VTH - VSETV (V)
MAXIMUM TRANSIENT DURATION (µs)
VCC1 = 5V
VCC2 = 0
SETD = FLOATING
GATE DISABLED ABOVE CURVE
10%
O
VEN/VSETV
tDELAY
tON
90%
10%
VCC2 + 5.5V
GATE
OtOFF
50%
Figure 3. Timing Diagram
MAX6819/MAX6820
SOT23 Power-Supply Sequencers
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
8_____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
©2005 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products, Inc.
6LSOT.EPS
PACKAGE OUTLINE, SOT 6L BODY
21-0058
1
1
G
Typical Operating Circuits
(continued)
SETDSETV
VCC2 GATE
DUAL-SUPPLY
BOARD OR µP
PRIMARY SUPPLY
(1.8V)
SECONDARY SUPPLY
(3.3V)
VCC1 GND
R2
R1
DC/DC
MAX6820
Pin Configurations (continued)
GND
SETDSETV
16VCC2
5GATE
VCC1
MAX6820
SOT23-6
2
34
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)