19-1951; Rev 3; 12/05
SOT23 Power-Supply Sequencers
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 R
DS-
ON
voltage drop. The devices can be connected to
support various supply sequencing priorities such as
V
I/O
before V
CORE
or V
CORE
before V
I/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
(V
PRIMARY GOOD
to V
SECONDARY 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.
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
Ordering Information
PART
MAX6819UT-T
MAX6820UT-T
TEMP RANGE
-40°C to +125°C
-40°C to +125°C
PIN-
PACKAGE
6 SOT23-6
6 SOT23-6
TOP
MARK
AARF
AARG
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
PRIMARY SUPPLY
(3.3V)
SECONDARY SUPPLY
(1.8V)
V
CC2
GATE
DUAL-SUPPLY
BOARD OR
µP
Applications
Dual-Voltage Microprocessors
Multivoltage Systems
Digital Signal Processors
Power PC™ Series Processors
MAX6819
V
CC1
GND
ON
SETV
EN
OFF
Pin Configurations
TOP VIEW
Pin Configurations and Typical Operating Circuits
continued at end of data sheet.
V
CC1
1
6
V
CC2
GND
2
MAX6819
5
GATE
Power PC is a trademark of IBM corp.
SETV
3
4
EN
SOT23-6
________________________________________________________________
Maxim Integrated Products
1
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.
SOT23 Power-Supply Sequencers
MAX6819/MAX6820
ABSOLUTE MAXIMUM RATINGS
Referenced to GND
V
CC1
, V
CC2
, EN .....................................................-0.3V to +6.0V
SETV, SETD..................-0.3V to the higher of (V
CC1
+ 0.3V) and
(V
CC2
+ 0.3V)
GATE ...................................................................-0.3V to +12.0V
Input Current/Output Current (all pins) ...............................20mA
Continuous Power Dissipation (T
A
= +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
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
(V
CC1
or V
CC2
> +2.125V to +5.5V, T
A
= -40°C to +125°C, unless otherwise specified. Typical values are at T
A
= +25°C.) (Note 1)
PARAMETER
Operating Voltage Range
V
CC1
, V
CC2
Supply Current
V
CC1
, V
CC2
Disable Mode Current
V
CC1
, V
CC2
Slew Rate (Note 3)
Undervoltage Lockout (UVLO)
SETV Threshold
SETV Input Current
SETV Threshold Hysteresis
SETV to GATE Delay
SETD Ramp Current (MAX6820)
SETD Voltage (MAX6820)
SETD Threshold Hysteresis
(MAX6820)
GATE Turn-On Time
GATE Turn-Off Time
t
ON
t
OFF
t
DELAY
I
SETD
V
SETD
V
UVLO
V
TH
V
SETV
rising, enables GATE
(Note 3)
V
SETV
falling, disables GATE
V
SETV
> V
TH
, V
EN
≥
2V (MAX6819)
V
CC1
or V
CC2
> +2.125V
V
CC1
or V
CC2
> +2.125V
V
SETD
falling
C
GATE
= 1500pF, V
CC2
= +3.3V, V
GATE
= +7.8V
C
GATE
= 1500pF, V
CC2
= +3.3V, V
GATE
= +0.5V
With respect to V
CC2
(Note 2)
R
GATE
> 50MΩ to V
CC2
With respect to V
CC2
(Note 2)
R
GATE
> 5MΩ to V
CC2
V
CC1
or V
CC2
> +2.125V to + 5.5V
4.5
4.0
0.5
140
400
1.210
SYMBOL
V
CC1
,
V
CC2
I
CC
(Note 2)
V
CC1
= V
CC2
= +3.3V
V
CC1
= V
CC2
= +3.3V, EN = GND
MAX6819
MAX6820 (Note 4)
6
1.2 / t
DELAY
2.0
1.875
0.602
0.618
10
-1
200
500
1.242
-62
1.5
30
5.5
6.0
V
6.0
0.4
2.0
V
10
280
600
1.273
2.125
0.634
100
CONDITIONS
MIN
0.9
60
20
TYP
MAX
5.5
120
UNITS
V
µA
µA
V/s
V
V
nA
%
ms
nA
V
mV
ms
µs
GATE Voltage
V
GATE
EN Input Voltage
V
IL
V
IH
Note 1:
Note 2:
Note 3:
Note 4:
100% production tested at T
A
= +25°C. Specifications over temperature limit are guaranteed by design.
Either V
CC1
or V
CC2
must be > 2.125V. The other supply can go to 0.
Guaranteed by design, not production tested.
t
DELAY
(s) = 2.48
✕
10
6
✕
C
SET
2
_______________________________________________________________________________________
SOT23 Power-Supply Sequencers
MAX6819/MAX6820
Typical Operating Characteristics
(T
A
= +25°C, unless otherwise noted.)
t
DELAY
vs. TEMPERATURE
240
230
220
t
DELAY
(ms)
210
200
190
180
170
160
150
-40 -20
0
20
40
60
80 100 120
(MAX6819)
MAX6819 toc01
GATE TURN-ON TIME
MAX6819 toc02
250
V
GATE
5V/div
C
LOAD
= 1500pF
1ms/div
TEMPERATURE (°C)
GATE TURN-OFF TIME
MAX6819 toc03
V
CC2
vs. GATE VOLTAGE
MAX6819 toc04
12
10
V
SETV
500mV/div
8
V
GATE
(V)
6
4
2
V
CC1
= +3.3V
V
SETV
= 1V
V
GATE
5V/div
C
LOAD
= 1500pF
0
20µs/div
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
V
CC2
(V)
V
CC2
vs. GATE VOLTAGE
MAX6819 toc05
V
CC2
vs. GATE VOLTAGE
MAX6819 toc06
12
10
8
V
GATE
(V)
12
10
8
V
GATE
(V)
6
4
2
0
0
V
CC1
= 0
V
SETV
= 1V
6
4
2
0
V
CC1
= +3.3V
V
SETV
= V
CC2
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
V
CC2
(V)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
V
CC2
(V)
_______________________________________________________________________________________
3
SOT23 Power-Supply Sequencers
MAX6819/MAX6820
Typical Operating Characteristics (continued)
(T
A
= +25°C, unless otherwise noted.)
V
SETV
vs. TEMPERATURE
MAX6819 toc07
SUPPLY CURRENT vs. TEMPERATURE
V
EN
= 2V
V
SETV
= 2V
V
CC1
= +3.3V
V
CC2
= +5V
MAX6819 toc08
0.65
0.64
0.63
V
SETV
(V)
0.62
0.61
0.60
0.59
-40 -20
0
20
40
60
80
100 120
TEMPERATURE (°C)
114
112
I
CC2
SUPPLY CURRENT (µA)
110
108
106
104
102
100
V
EN
= 2V
V
SETV
= 2V
V
CC2
= +3.3V
V
CC1
= +5V
-40 -20
0
20
40
60
80
100
I
CC1
120
TEMPERATURE (°C)
I
CC2
vs. V
CC2
MAX6819 toc09
I
CC2
vs. V
CC2
140
120
100
I
CC2
(µA)
80
60
V
CC1
= 3.3V
V
EN
= 2V
V
SETV
= 2V
MAX6819 toc10
140
120
100
I
CC2
(µA)
80
60
40
20
0
0
1
2
3
V
CC2
(V)
4
5
6
V
CC1
= 0
V
EN
= 2V
V
SETV
= 2V
40
20
0
0
1
2
3
V
CC2
(V)
4
5
6
4
_______________________________________________________________________________________
SOT23 Power-Supply Sequencers
Pin Description
PIN
NAME
MAX6819
1
2
3
MAX6820
1
2
3
V
CC1
GND
SETV
Supply Voltage 1. Either V
CC1
or V
CC2
must be greater than the UVLO to enable
external MOSFET drive.
Ground
Sequence Threshold Set. Connect to an external resistor-divider network to set the
V
CC1
threshold that enables GATE turn-on. The internal reference is 0.618V.
Active-High Enable. GATE drive is enabled t
DELAY
after EN is driven high. GATE
drive is immediately disabled when EN is driven low. Connect to the higher of V
CC1
and V
CC2
if not used.
GATE Delay Set Input. Connect an external capacitor from SETD to GND to adjust
the delay from SETV > V
TH
to GATE turn-on. t
DELAY
(s) = 2.484 x 10
6
x C
SET
(F).
GATE Drive Output. GATE drives an external n-channel MOSFET to connect V
CC2
to
the load. GATE drive enables t
DELAY
after SETV exceeds V
TH
and ENABLE is driven
high. GATE drive is immediately disabled when SETV drops below V
TH
or ENABLE is
driven low. When enabled, an internal charge pump drives GATE to V
CC2
+ 5.5V to
fully enhance the external n-channel MOSFET.
Supply Voltage 2. Either V
CC1
or V
CC2
must be greater than the UVLO to enable
external MOSFET drive.
V
CC1
V
CC2
V
CC2
OUT
GATE
MAX6819/MAX6820
FUNCTION
4
—
EN
—
4
SETD
5
5
GATE
6
6
V
CC2
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 (V
GS
) of +5.5V
(typ). The charge pump fully enhances the MOSFET to
yield a low drain-to-source impedance (R
DS(ON)
) for
reduced switch voltage drop. The MOSFET is never dri-
UVLO
SETV
SEQUENCE
DELAY/
LOGIC
0.62V
GATE DRIVE
CHARGE PUMP
GND
( ) FOR MAX6820 ONLY
EN (SETD)
Figure 1. Functional Diagram
ven on unless the sequencer can provide a minimum
V
GS
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 V
CC1
or V
CC2
is
greater than 2.125V (Figure 1 and Figure 2).
_______________________________________________________________________________________
5
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