MAX6819UT-T-MAX6820UT-T Fast Delivery |IC PHOENIX CO.,LIMITED

MAX6819UT-T ,200 ms, power-supply sequencerFeaturesThe MAX6819/MAX6820 are power-supply sequencers Adjustable Primary Supply Voltage Monitorf ..
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MAX6819UT-T-MAX6820UT-T
200 ms, power-supply sequencer
General Description
The MAX6819/MAX6820 are power-supply sequencers
for dual-voltage microprocessors (µPs) and multivolt-
age 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 charac-
teristics cannot be guaranteed (supplies come from a
multivoltage system 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.
Applications
Dual-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 Sequencers
19-1951; Rev 2; 4/02
Ordering Information
Pin Configurations
Products must be ordered in 2,500 piece increments.
Typical Operating Circuits
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 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 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
ELECTRICAL CHARACTERISTICS
MAX6819/MAX6820
SOT23 Power-Supply Sequencers
tDELAY vs. TEMPERATURE
MAX6819 toc01
TEMPERATURE (°C)
tDELAY
(ms)
1ms/div
GATE TURN-ON TIME
VGATE
5V/div
MAX6819 toc02
20µs/div
GATE TURN-OFF TIME
VSETV
500mV/div
VGATE
5V/div
MAX6819 toc032.01.50.51.02.53.03.54.04.55.0
VCC2 vs. VGATE
MAX6819 toc04
VCC2 (V)
GATE
(V)2.01.50.51.02.53.03.54.04.55.0
VCC2 vs. VGATE
MAX6819 toc05
VCC2 (V)
GATE
(V)2.01.50.51.02.53.03.54.04.55.0
VCC2 vs. VGATE
MAX6819 toc06
VCC2 (V)
GATE
(V)
Typical Operating Characteristics
(TA = +25°C, unless otherwise noted.)
MAX6819/MAX6820
SOT23 Power-Supply Sequencers
VSETV vs. TEMPERATURE
MAX6819 toc07
TEMPERATURE (°C)
SETV
(V)
SUPPLY CURRENT vs. TEMPERATURE
MAX6819 toc08
TEMPERATURE (°C)
SUPPLY CURRENT (
ICC2 vs. VCC2
MAX6819 toc09
VCC2 (V)
ICC2
ICC2 vs. VCC2
MAX6819 toc10
VCC2 (V)
ICC2
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 sec-
ondary 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
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 VCC1voltage at
which VCC2turn-on is acceptable. To monitor voltages
higher than the threshold voltage, connect external
resistors as a voltage-divider to SETV, and calculate the
minimum VCCturn-on voltage as follows:
R1 = R2 ((VTRIP / VTH)- 1)
where VTRIPis 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 VCC1nor 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 VCC1or 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

Partno	Mfg	Dc	Qty	Available	Descript
MAX6819UT-T \|MAX6819UTT	MAX	N/a	25	avai	200 ms, power-supply sequencer
MAX6819UT-T \|MAX6819UTT	MAXIM	N/a	1887	avai	200 ms, power-supply sequencer
MAX6820UT-T \|MAX6820UTT	MAXIM	N/a	459	avai	Power-supply sequencer