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19-1951; Rev 2; 4/02
SOT23 Power-Supply Sequencers
General Description
The MAX6819/MAX6820 are power-supply sequencers for dual-voltage microprocessors (Ps) 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 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 reference/comparator with externally adjustable thresholds to monitor the primary power supply. When the primary supply is below the desired threshold, an external 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 RDSON 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 (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 (-40C to +125C) and are available in space-saving 6-pin SOT23 packages.
Features
o Adjustable Primary Supply Voltage Monitor (Monitors Down to 0.62V) o Internal Charge Pump to Enhance External Secondary Supply N-Channel MOSFET Switch o Delay from Primary Supply Good to Secondary Supply Enabled Factory Fixed 200ms (MAX6819) Capacitor Adjustable (MAX6820) o Logic Driven ENABLE Input (MAX6819) o Immune to Short Voltage Transients o Few External Components o -40C to +125C Operating Temperature Range o Small 6-Pin SOT23 Package
MAX6819/MAX6820
Ordering Information
PART MAX6819UT-T MAX6820UT-T TEMP RANGE -40C to +125C -40C to +125C PINPACKAGE 6 SOT23-6 6 SOT23-6 TOP MARK AARF AARG
Products must be ordered in 2,500 piece increments.
Typical Operating Circuits
PRIMARY SUPPLY (3.3V) SECONDARY SUPPLY (1.8V) VCC2 GATE DUAL-SUPPLY BOARD OR P
MAX6819
VCC1 GND
Applications
Dual-Voltage Microprocessors Multivoltage Systems Digital Signal Processors Power PCTM Series Processors
TOP VIEW
ON SETV EN OFF
Pin Configurations
Pin Configurations and Typical Operating Circuits continued at end of data sheet.
VCC1 1
6
VCC2
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 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 = +70C) 6-Pin SOT23 (derate 8.7mW/C above +70C)............696mW Operating Temperature Range .........................-40C to +125C Junction Temperature ......................................................+150C Storage Temperature Range .............................-65C to +150C Lead Temperature (soldering 10s) ..................................+300C
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
(VCC1 or VCC2 > +2.125V to +5.5V, TA = -40C to +125C, unless otherwise specified. Typical values are at TA = +25C.) (Note 1)
PARAMETER Operating Voltage Range VCC1, VCC2 Supply Current VCC1, VCC2 Disable Mode Current VCC1, VCC2 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 tON tOFF tDELAY ISETD VSETD VUVLO VTH VSETV rising, enables GATE (Note 3) VSETV falling, disables GATE VSETV > VTH, VEN 2V (MAX6819) VCC1 or V CC2 > +2.125V VCC1 or VCC2 > +2.125V VSETD falling CGATE = 1500pF, VCC2 = +3.3V, VGATE = +7.8V CGATE = 1500pF, VCC2 = +3.3V, VGATE = +0.5V With respect to VCC2 (Note 2) RGATE > 50M to VCC2 With respect to VCC2 (Note 2) RGATE > 5M to VCC2 VCC1 or VCC2 > +2.125V to + 5.5V 4.5 4.0 0.5 140 400 1.210 SYMBOL VCC1, VCC2 ICC (Note 2) VCC1 = VCC2 = +3.3V VCC1 = VCC2 = +3.3V, EN = GND MAX6819 MAX6820 (Note 4) 6 1.2/tDELAY 1.875 0.602 2.0 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 A A V/s V V nA % ms nA V mV ms s
GATE Voltage
VGATE
EN Input Voltage
VIL VIH
Note 1: Note 2: Note 3: Note 4:
100% production tested at TA = +25C. Specifications over temperature limit are guaranteed by design. Either VCC1 or VCC2 must be > 2.125V. The other supply can go to 0. Guaranteed by design, not production tested. tDELAY (s) = 2.48 106 CSET
2
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SOT23 Power-Supply Sequencers
Typical Operating Characteristics
(TA = +25C, unless otherwise noted.)
MAX6819/MAX6820
tDELAY vs. TEMPERATURE
240 230 220 tDELAY (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
VGATE 5V/div
CLOAD = 1500pF 1ms/div
TEMPERATURE (C)
GATE TURN-OFF TIME
MAX6819 toc03
VCC2 vs. VGATE
MAX6819 toc04
12 10 VSETV 500mV/div 8 VGATE (V) 6 4 2 VCC1 = +3.3V VSETV = 1V
VGATE 5V/div
CLOAD = 1500pF 0 20s/div 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 VCC2 (V)
VCC2 vs. VGATE
MAX6819 toc05
VCC2 vs. VGATE
MAX6819 toc06
12 10 8 VGATE (V) 6 4 2 0 0
12 10 8 VGATE (V)
VCC1 = 0 VSETV = 1V
6 4 2 0
VCC1 = +3.3V VSETV = VCC2
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 VCC2 (V)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 VCC2 (V)
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3
SOT23 Power-Supply Sequencers MAX6819/MAX6820
Typical Operating Characteristics (continued)
(TA = +25C, unless otherwise noted.)
VSETV vs. TEMPERATURE
MAX6819 toc07
SUPPLY CURRENT vs. TEMPERATURE
VEN = 2V VSETV = 2V VCC1 = +3.3V VCC2 = +5V
MAX6819 toc08
0.65 0.64 0.63 VSETV (V) 0.62 0.61 0.60 0.59 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (C)
114 112 ICC2 SUPPLY CURRENT (A) 110 108 106 104 102 100 VEN = 2V VSETV = 2V VCC2 = +3.3V VCC1 = +5V -40 -20 0 20 40 60 80 100 ICC1
120
TEMPERATURE (C)
ICC2 vs. VCC2
MAX6819 toc09
ICC2 vs. VCC2
140 120 100 ICC2 (A) 80 60 VCC1 = 3.3V VEN = 2V VSETV = 2V
MAX6819 toc10
140 120 100 ICC2 (A) 80 60 40 20 0 0 1 2 3 VCC2 (V) 4 5 6 VCC1 = 0 VEN = 2V VSETV = 2V
40 20 0 0 1 2 3 VCC2 (V) 4
5
6
4
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SOT23 Power-Supply Sequencers
Pin Description
PIN NAME MAX6819 1 2 3 MAX6820 1 2 3 VCC1 GND SETV Supply Voltage 1. Either VCC1 or VCC2 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 VCC1 threshold that enables GATE turn-on. The internal reference is 0.618V. 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. 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). 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. Supply Voltage 2. Either VCC1 or VCC2 must be greater than the UVLO to enable external MOSFET drive.
VCC1 VCC2 VCC2 OUT GATE
MAX6819/MAX6820
FUNCTION
4
--
EN
--
4
SETD
5
5
GATE
6
6
VCC2
Detailed Description
Many dual-supply processors or multivoltage boards require one power supply to rise to the proper operating voltage before another supply is applied. Improper sequencing can lead to chip latchup, incorrect device initiation, or long-term reliability degradation. If the various 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 turnon/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 Nchannel 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 internal 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
UVLO
SETV
SEQUENCE DELAY/ LOGIC 0.62V
GATE DRIVE CHARGE PUMP
GND ( ) FOR MAX6820 ONLY EN (SETD)
Figure 1. Functional Diagram
reduced switch voltage drop. The MOSFET is never driven 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, regardless of the voltage level, provided that VCC1 or VCC2 is greater than 2.125V (Figure 1 and Figure 2).
5
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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
Gate Drive Characteristics
The MAX6819/MAX6820 internal charge pump drives the N-channel MOSFET with a gate-to-source voltage (V GS ) 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.
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 resistors can be used.
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 monitoring is not desired, connect SETV to VCC1 or VCC2 > 0.62V (Figure 3).
Sequencing Three or More Supplies
VCC1 R1
MAX6820
SETV SETD CSET
R2
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 independent 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.
Figure 2. tDELAY (MAX6820 ONLY) and VTH Adjust
Negative-Going Voltage Transient Immunity
The MAX6819/MAX6820 power-supply voltage sequencers are relatively immune to short-duration (pulse width), negative-going voltage transients (Figure 5). However, the amplitude of the transient is inversely proportional to its pulse width.
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-tosource on impedance. For highest supply accuracy/ lowest voltage drop, select a MOSFET with an appropriate drain-to-source on impedance for a gate-to-source bias of 4.5V to 6.0V.
Chip Information
TRANSISTOR COUNT: 638 PROCESS: BiCMOS
6
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SOT23 Power-Supply Sequencers MAX6819/MAX6820
VEN/VSETV O VCC2 + 5.5V
90%
50% tON
GATE O tDELAY
10%
tOFF
10%
Figure 3. Timing Diagram
5(V) PRIMARY VOLTAGE SUPPLY 3.3(V) SECONDARY VOLTAGE SUPPLY 1.8(V) THIRD VOLTAGE SUPPLY
VCC2
GATE
VCC2
GATE MULTISUPPLY BOARD OR P
MAX6819 MAX6820 GND VCC1
R1 SETV R2 SETD/EN R4 R3
MAX6819 MAX6820 GND VCC1
SETV
SETD/EN
Figure 4. Sequencing Three Power Supplies
20 MAXIMUM TRANSIENT DURATION (s) 18 16 14 12 10 8 6 4 2 0 0.01 0.1 1 SETV THRESHOLD OVERDRIVE, VTH - VSETV (V)
GATE DISABLED ABOVE CURVE
VCC1 = 5V VCC2 = 0 SETD = FLOATING
Figure 5. Maximum Transient Duration vs. SETV Threshold in Overdrive _______________________________________________________________________________________ 7
SOT23 Power-Supply Sequencers MAX6819/MAX6820
Typical Operating Circuits (continued)
PRIMARY SUPPLY (1.8V) DC/DC SECONDARY SUPPLY (3.3V) VCC2 GATE DUAL-SUPPLY BOARD OR P
Pin Configurations (continued)
VCC1 1 6 VCC2
GND 2
MAX6820
5
GATE
SETV 3
4
SETD
MAX6820
VCC1 R1 SETV R2 SETD GND
SOT23-6
Package Information
6LSOT.EPS
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 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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