MAX6820UT-T [MAXIM]
Power Supply Switching Circuit ; 电源开关电路\n
| 型号： | MAX6820UT-T |
| 厂家： | 
MAXIM INTEGRATED PRODUCTS |
| 描述： | Power Supply Switching Circuit
|
| 文件： | 总8页 (文件大小：213K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
19-1951; Rev 0; 1/01
SOT23 Power-Supply Sequencers
General Description
Features
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.
ꢀ 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
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
ꢀ -40°C to +125°C Operating Temperature Range
ꢀ Small 6-Pin SOT23 Package
Ordering Information
TOP
MARK
PIN-
PACKAGE
PART
TEMP. RANGE
MAX6819UT-T
MAX6820UT-T*
-40°C to +125°C
-40°C to +125°C
6 SOT23-6
6 SOT23-6
AARF
AARG
N-channel MOSFET switch to provide a very low R
ON
DS-
voltage drop. The devices can be connected to
support various supply sequencing priorities such as
before V or V before V
*Future product–contact factory for availablitly.
V
I/O
.
I/O
CORE
CORE
Products must be ordered in 2,500 piece increments.
The MAX6819 features a logic-driven EN input to
enable/disable the external MOSFET drive and includes
an internally fixed 200ms enable timeout period
Typical Operating Circuits
PRIMARY SUPPLY
(3.3V)
(V
to V
). The
SECONDARY ENABLE
PRIMARY GOOD
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.
SECONDARY SUPPLY
(1.8V)
V
V
GATE
CC2
DUAL-SUPPLY
BOARD OR µP
MAX6819
GND
EN
CC1
Applications
Dual-Voltage Microprocessors
Multivoltage Systems
ON
SETV
OFF
Digital Signal Processors
Power PC™ Series Processors
Pin Configurations
TOP VIEW
Pin Configurations and Typical Operating Circuits
continued at end of data sheet.
V
1
2
3
6
5
4
V
CC2
CC1
MAX6819
GND
GATE
EN
Power PC is a trademark of IBM corp.
SETV
SOT23-6
________________________________________________________________ Maxim Integrated Products
1
For price, delivery, and to place orders, please contact Maxim Distribution at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
SOT23 Power-Supply Sequencers
ABSOLUTE MAXIMUM RATINGS
Referenced to GND
, V
Continuous Power Dissipation (T = +70°C)
6-Pin SOT23 (derate 8.7mW/°C above +70°C)............696mW
A
V , EN.....................................................-0.3V to +6.0V
CC1 CC2
SETV, SETD..................-0.3V to the higher of (V
+ 0.3V) and
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
CC1
(V
CC2
+ 0.3V)
GATE ...................................................................-0.3V to +12.0V
Input Current/Output Current (all pins) ...............................20mA
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
or V
> +2.125V to +5.5V, T = -40°C to +125°C, unless otherwise specified. Typical values are at T = +25°C.) (Note 1)
CC1
CC2
A
A
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
5.5
UNITS
V
,
CC1
Operating Voltage Range
(Note 2)
0.9
V
V
CC2
V
V
V
, V
Supply Current
Disable Mode Current
Slew Rate
I
V
V
= V
= V
= +3.3V
60
20
120
µA
µA
V/s
V
CC1 CC2
CC
CC1
CC1
CC2
CC2
, V
= +3.3V, EN = GND
CC1 CC2
, V
CC1 CC2
(Note 3)
6
2.0
0.618
10
2.125
0.634
100
Undervoltage Lockout (UVLO)
SETV Threshold
V
1.875
0.602
UVLO
V
V
V
rising, enables GATE
SETV
TH
nA
%
SETV Input Current
(Note 3)
-1
SETV Threshold Hysteresis
SETV to GATE Delay
V
V
V
V
falling, disables GATE
SETV
SETV
CC1
CC1
200
280
ms
t
> V , V ≥ 2V (MAX6819)
140
400
DELAY
TH EN
SETD Ramp Current (MAX6820)
SETD Voltage (MAX6820)
I
or V
or V
> +2.125V
> +2.125V
500
600
nA
V
SETD
CC2
CC2
1.242
1.273
V
1.210
SETD
SETD Threshold Hysteresis
(MAX6820)
V
falling
-62
mV
SETD
1.5
30
10
ms
GATE Turn-On Time
GATE Turn-Off Time
t
C
C
= 1500pF, V
= 1500pF, V
= +3.3V, V
= +3.3V, V
= +7.8V
= +0.5V
0.5
ON
GATE
CC2
GATE
µs
t
OFF
GATE
CC2
GATE
With respect to V
(Note 2)
CC2
CC2
4.5
4.0
5.5
6.0
R
GATE
> 50MΩ to V
GATE Voltage
V
V
V
GATE
With respect to V
(Note 2)
CC2
6.0
0.4
R
GATE
> 5MΩ to V
CC2
V
IL
EN Input Voltage
V
or V
> +2.125V to + 5.5V
CC2
CC1
V
2.0
IH
Note 1: 100% production tested at T = +25°C. Specifications over temperature limit are guaranteed by design.
A
Note 2: Either V
or V
must be > 2.125V. The other supply can go to 0.
CC1
CC2
Note 3: Guaranteed by design, not production tested.
2
_______________________________________________________________________________________
SOT23 Power-Supply Sequencers
Typical Operating Characteristics
(T = +25°C, unless otherwise noted.)
A
t
vs. TEMPERATURE
GATE TURN-ON TIME
MAX6819 toc02
DELAY
250
240
230
220
210
200
190
180
170
160
150
V
GATE
5V/div
(MAX6819)
C
LOAD
= 1500pF
-40 -20
0
20 40 60 80 100 120
1ms/div
TEMPERATURE (°C)
GATE TURN-OFF TIME
V
vs. V
GATE
CC2
MAX6819 toc03
12
10
8
V
SETV
500mV/div
V
V
= +3.3V
= 1V
CC1
SETV
6
V
GATE
5V/div
4
2
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)
V
CC2
V
vs. V
V
vs. V
GATE
CC2
GATE
CC2
12
10
8
12
10
8
6
V
V
= +3.3V
6
CC1
V
V
= 0
SETV
CC1
= V
SETV
CC2
= 1V
4
4
2
2
0
0
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
(V)
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
(V)
V
CC2
V
CC2
_______________________________________________________________________________________
3
SOT23 Power-Supply Sequencers
Typical Operating Characteristics (continued)
(T = +25°C, unless otherwise noted.)
A
V
vs. TEMPERATURE
SUPPLY CURRENT vs. TEMPERATURE
SETV
0.65
0.64
0.63
0.62
0.61
0.60
0.59
114
112
110
108
106
104
102
100
V
V
V
V
= 2V
EN
= 2V
SETV
CC1
CC2
I
= +3.3V
= +5V
CC2
I
CC1
V
V
V
V
= 2V
EN
= 2V
SETV
CC2
CC1
= +3.3V
= +5V
-40 -20
0
20 40 60 80 100 120
-40 -20
0
20 40 60 80 100 120
TEMPERATURE (°C)
TEMPERATURE (°C)
I
vs. V
I
vs. V
CC2
CC2
CC2
CC2
140
140
120
100
120
100
80
60
40
80
60
V
V
V
= 3.3V
= 2V
CC1
= 2V
EN
V
V
V
= 0
CC1
= 2V
40
SETV
EN
SETV
= 2V
20
0
20
0
0
1
2
3
4
5
6
0
1
2
3
4
5
6
V
CC2
(V)
V
CC2
(V)
4
_______________________________________________________________________________________
SOT23 Power-Supply Sequencers
Pin Description
PIN
FUNCTION
must be greater than the UVLO to enable
NAME
MAX6819
MAX6820
Supply Voltage 1. Either V
external MOSFET drive.
or V
CC2
CC1
1
2
3
1
2
3
V
CC1
GND
SETV
Ground
Sequence Threshold Set. Connect to an external resistor-divider network to set the
threshold that enables GATE turn-on. The internal reference is 0.618V.
V
CC1
Active-High Enable. GATE drive is enabled t
after EN is driven high. GATE
DELAY
drive is immediately disabled when EN is driven low. Connect to the higher of V
4
—
EN
CC1
and V
if not used.
CC2
GATE Delay Set Input. Connect an external capacitor from SETD to GND to adjust
the delay from SETV > V to GATE turn-on. t (s) = 2.484e6 x C (F).
—
4
SETD
TH
DELAY
SET
GATE Drive Output. GATE drives an external N-channel MOSFET to connect V
to
CC2
the load. GATE drive enables t
after SETV exceeds V and ENABLE is driven
TH
DELAY
5
6
5
6
GATE
high. GATE drive is immediately disabled when SETV drops below V or ENABLE is
TH
driven low. When enabled, an internal charge pump drives GATE to V
fully enhance the external N-channel MOSFET.
+ 5.5V to
CC2
Supply Voltage 2. Either V
external MOSFET drive.
or V
must be greater than the UVLO to enable
CC2
CC1
V
CC2
V
CC1
V
CC2
Detailed Description
V
OUT
CC2
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.
GATE
UVLO
SEQUENCE
DELAY/
LOGIC
SETV
GND
GATE DRIVE
CHARGE PUMP
0.62V
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.
EN (SETD)
( ) FOR MAX6820 ONLY
Figure 1. Functional Diagram
reduced switch voltage drop. The MOSFET is never dri-
ven on unless the sequencer can provide a minimum
enhancement, ensuring that the switch MOSFET
never operates in its higher impedance linear range.
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
V
GS
by providing a gate-to-source voltage (V ) of +5.5V
GS
Either supply may act as the primary source, regard-
(typ). The charge pump fully enhances the MOSFET to
less of the voltage level, provided that V
greater than 2.125V (Figure 1 and Figure 2).
or V
is
CC1
CC2
yield a low drain-to-source impedance (R
) for
DS(ON)
_______________________________________________________________________________________
5
SOT23 Power-Supply Sequencers
Gate Drive Characteristics
Applications Information
The MAX6819/MAX6820 internal charge pump drives
the N-channel MOSFET with a gate-to-source voltage
Adjusting t
DELAY
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
(V ) of 5.5V, ensuring low MOSFET on-resistance
GS
R
. The charge pump drives the high-impedance
DS(ON)
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.
(C
) between SETD and GND to adjust the delay
time (Figure 2). Calculate the sequence delay time as
follows:
SET
The external pass MOSFET is disabled, and charge
t
(s) = 2.484e6 x C
SET
DELAY
pump circuitry is turned off when neither V
are above the 1.875V UVLO or EN is low.
nor V
CC2
CC1
Setting Threshold Voltage V
TH
The threshold voltage is the minimum V
voltage at
CC1
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-
which V
turn-on is acceptable. To monitor voltages
CC2
higher than the threshold voltage, connect external
resistors as a voltage-divider to SETV, and calculate
V
TH
as follows:
R1 = R2 (V / V
- 1)
TH
TRIP
Where V is the desired threshold voltage and V
TH
=
TRIP
0.618V (Figure 2).
ing is not desired, connect SETV to V
0.62V.
or V
>
CC2
CC1
Since SETV input current is 10nA (typ), high value resis-
tors can be used.
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.
V
CC1
MAX6820
R1
R2
SETV
SETD
C
SET
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 4.)
However, the amplitude of the transient is inversely pro-
portional to its pulse width.
Figure 2. t
(MAX6820 ONLY) and V Adjust
TH
DELAY
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
(R ) determine the voltage drop, the on characteristics
DS
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.
Chip Information
TRANSISTOR COUNT: 638
PROCESS: BiCMOS
6
_______________________________________________________________________________________
SOT23 Power-Supply Sequencers
V
/V
EN SETV
50%
O
t
ON
V
CC2
+ 5.5V
90%
GATE
O
10%
10%
t
OFF
t
DELAY
Figure 3. Timing Diagram
5(V) PRIMARY VOLTAGE SUPPLY
3.3(V) SECONDARY VOLTAGE SUPPLY
1.8(V) THIRD VOLTAGE SUPPLY
GATE
GATE
V
V
V
V
CC2
CC2
MULTISUPPLY
BOARD OR µP
MAX6819
MAX6820
MAX6819
MAX6820
GND
CC1
GND
CC1
R
R
R
R
1
3
SETV SETD/EN
SETV SETD/EN
2
4
Figure 4. Sequencing Three Power Supplies
V
SETV
2V/div
V
GATE
5V/div
0
10µs/div
Figure 5. Transient Immunity
_______________________________________________________________________________________
7
SOT23 Power-Supply Sequencers
Typical Operating Circuits
(continued)
Pin Configurations (continued)
PRIMARY SUPPLY
(1.8V)
V
1
2
3
6
5
4
V
CC2
CC1
DC/DC
MAX6820
SECONDARY SUPPLY
(3.3V)
GND
GATE
SETD
GATE
V
V
CC2
DUAL-SUPPLY
BOARD OR µP
SETV
MAX6820
GND
CC1
SOT23-6
R1
R2
SETV
SETD
Package Information
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
© 2001 Maxim Integrated Products
Printed USA
is a registered trademark of Maxim Integrated Products.
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