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1
LTC1157
3.3V Dual Micropower
High-Side/Low-Side MOSFET Driver
The LTC1157 dual 3.3V micropower MOSFET gate driver
makes it possible to switch either supply or ground
reference loads through a low R
DS(ON)
N-channel switch
(N-channel switches are required at 3.3V because P-
channel MOSFETs do not have guaranteed R
DS(ON)
with
V
GS
3.3V). The LTC1157 internal charge pump boosts
the gate drive voltage 5.4V above the positive rail (8.7V
above ground), fully enhancing a logic level N-channel
switch for 3.3V high-side applications and a standard N-
channel switch for 3.3V low-side applications. The gate
drive voltage at 5V is typically 8.8V above supply (13.8V
above ground), so standard N-channel MOSFET switches
can be used for both high-side and low-side applications.
Micropower operation, with 3
A standby current and
80
A operating current, makes the LTC1157 well suited
for battery-powered applications.
The LTC1157 is available in both 8-pin DIP and SOIC.
S
FEATURE
s
Allows Lowest Drop 3.3V Supply Switching
s
Operates on 3.3V or 5V Nominal Supplies
s
3 Microamps Standby Current
s
80 Microamps ON Current
s
Drives Low Cost N-Channel Power MOSFETs
s
No External Charge Pump Components
s
Controlled Switching ON and OFF Times
s
Compatible with 3.3V and 5V Logic Families
s
Available in 8-Pin SOIC
U
S
A
O
PPLICATI
s
Notebook Computer Power Management
s
Palmtop Computer Power Management
s
P-Channel Switch Replacement
s
Battery Charging and Management
s
Mixed 5V and 3.3V Supply Switching
s
Stepper Motor and DC Motor Control
s
Cellular Telephones and Beepers
D
U
ESCRIPTIO
U
A
O
PPLICATI
TYPICAL
+
V
S
GND
G2
G1
IN2
IN1
LTC1157
3.3V
LOGIC
(8.7V)
(8.7V)
IRLR024
IRLR024
3.3V
LOAD
3.3V
LOAD
10
F
3.3V
LTC1157 TA01
Ultra Low Voltage Drop 3.3V Dual High-Side Switch
Gate Voltage Above Supply
SUPPLY VOLTAGE (V)
2.0
0
GATE VOLTAGE SUPPLY VOLTAGE (V)
2
4
6
8
3.0
4.0
5.0
6.0
LTC1157 TA02
10
12
2.5
3.5
4.5
5.5
2
LTC1157
LTC1157C
SYMBOL
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
I
Q
Quiescent Current OFF
V
S
= 3.3V, V
IN1
= V
IN2
= 0V (Note 1)
3
10
A
Quiescent Current ON
V
S
= 3.3V, V
IN
= 3.3V (Note 2)
80
160
A
V
S
= 5V, V
IN
= 5V (Note 2)
180
400
A
V
INH
Input High Voltage
q
70%
V
S
V
V
INL
Input Low Voltage
q
15%
V
S
V
I
IN
Input Current
0V
V
IN
V
S
q
1
A
C
IN
Input Capacitance
5
pF
V
GATE
V
S
Gate Voltage Above Supply
V
S
= 3V
q
4.0
4.7
6.5
V
V
S
= 3.3V
q
4.5
5.4
7.0
V
V
S
= 5V
q
7.5
8.8
12.0
V
t
ON
Turn-ON Time
V
S
= 3.3V, C
GATE
= 1000pF
Time for V
GATE
> V
S
+ 1V
30
130
300
s
Time for V
GATE
> V
S
+ 2V
75
240
750
s
V
S
= 5V, C
GATE
= 1000pF
Time for V
GATE
> V
S
+ 1V
30
85
300
s
Time for V
GATE
> V
S
+ 2V
75
230
750
s
t
OFF
Turn-OFF Time
V
S
= 3.3V, C
GATE
= 1000pF
Time for V
GATE
< 0.5V
10
36
60
s
V
S
= 5V, C
GATE
= 1000pF
Time for V
GATE
< 0.5V
10
31
60
s
Supply Voltage ........................................... 0.3V to 7V
Any Input Voltage ............. (V
S
+ 0.3V) to (GND 0.3V)
Any Output Voltage ............. (V
S
+ 12V) to (GND 0.3V)
Current (Any Pin) ................................................. 50mA
A
U
G
W
A
W
U
W
A
R
BSOLUTE
XI
TI
S
Operating Temperature Range
LTC1157C ............................................... 0
C to 70
C
Storage Temperature Range ................ 65
C to 150
C
Lead Temperature (Soldering, 10 sec) ................. 300
C
W
U
U
PACKAGE/ORDER I FOR ATIO
ORDER PART
NUMBER
LTC1157CN8
ORDER PART
NUMBER
T
JMAX
= 100
C,
JA
= 130
C/ W
LTC1157CS8
T
JMAX
= 100
C,
JA
= 150
C/ W
ELECTRICAL C
C
HARA TERISTICS
V
S
= 2.7V to 5.5V, T
A
= 25
C, unless otherwise noted.
The
q
denotes specifications which apply over the full operating
temperature range.
Note 1: Quiescent current OFF is for both channels in OFF condition.
Note 2: Quiescent current ON is per driver and is measured independently.
S8 PART MARKING
1157
1
2
3
4
8
7
6
5
TOP VIEW
NC
GATE 1
GND
IN1
NC
GATE 2
V
S
IN2
N8 PACKAGE
8-LEAD PLASTIC DIP
1
2
3
4
8
7
6
5
TOP VIEW
NC
GATE 2
V
S
IN2
NC
GATE 1
GND
IN1
S8 PACKAGE
8-LEAD PLASTIC SO
3
LTC1157
C
C
HARA TERISTICS
U
W
A
TYPICAL PERFOR
CE
Standby Supply Current
Turn-OFF Time
Input Threshold Voltage
Standby Supply Current
Supply Current per Driver ON
Gate Drive Current
Gate Voltage Above Supply
Supply Current per Driver ON
SUPPLY VOLTAGE (V)
2.0
0
SUPPLY CURRENT (
A)
2
4
6
8
3.0
4.0
5.0
6.0
LTC1157 TPC01
10
12
2.5
3.5
4.5
5.5
V
IN1
= V
IN2
= 0V
T
A
= 25C
SUPPLY VOLTAGE (V)
2.0
0
SUPPLY CURRENT (
A)
100
200
300
400
3.0
4.0
5.0
6.0
LTC1157 TPC02
500
600
2.5
3.5
4.5
5.5
ONE INPUT = ON
OTHER INPUT = OFF
T
A
= 25C
Turn-ON Time
TEMPERATURE (C)
0
SUPPLY CURRENT (
A)
8
10
12
30
50
LTC1157 TPC07
6
4
10
20
40
60
70
2
0
V
S
= 5V
V
S
= 3.3V
TEMPERATURE (C)
0
SUPPLY CURRENT (
A)
200
250
300
30
50
LTC1157 TPC08
150
100
10
20
40
60
70
50
0
V
S
= 5V
V
S
= 3.3V
SUPPLY VOLTAGE (V)
2.0
0
GATE VOLTAGE SUPPLY VOLTAGE (V)
2
4
6
8
3.0
4.0
5.0
6.0
LTC1157 TPC03
10
12
2.5
3.5
4.5
5.5
SUPPLY VOLTAGE (V)
2.0
0
TURN-OFF TIME (
s)
10
20
30
40
3.0
4.0
5.0
6.0
LTC1157 TPC06
50
60
2.5
3.5
4.5
5.5
C
GATE
= 1000pF
TIME FOR V
GATE
< 0.5V
SUPPLY VOLTAGE (V)
2.0
0
INPUT THRESHOLD VOLTAGE (V) 0.5
1.0
1.5
2.0
3.0
4.0
5.0
6.0
LTC1157 TPC04
2.5
3.0
2.5
3.5
4.5
5.5
T
A
= 25C
GATE VOLTAGE ABOVE SUPPLY (V)
1
GATE DRIVE CURRENT (
A)
10
100
1000
0
4
6
8
0.1
2
10
LTC1157 TPC09
V
S
= 5V
V
S
= 3.3V
T
A
= 25C
SUPPLY VOLTAGE (V)
2.0
0
TURN-ON TIME (
s)
200
300
400
600
3.0
4.0
5.0
6.0
LTC1157 TPC05
800
1000
2.5
3.5
4.5
5.5
V
GS
= 5V
V
GS
= 2V
V
GS
= 1V
C
GATE
= 1000pF
4
LTC1157
PI FU CTIO S
U
U
U
Input Pins: The LTC1157 input pins are active high and
activate the charge pump circuitry when switched ON. The
LTC1157 logic inputs are high impedance CMOS gates
with ESD protection diodes to ground and supply and
therefore should not be forced beyond the power supply
rails.
Gate Drive Pins: The gate drive pin is either driven to
ground when the switch is turned OFF or driven above the
supply rail when the switch is turned ON. This pin is a
relatively high impedance when driven above the rail (the
equivalent of a few hundred k
). Care should be taken to
minimize any loading of this pin by parasitic resistance to
ground or supply.
Supply Pin:
The supply pin of the LTC1157 should never
be forced below ground as this may result in permanent
damage to the device. A 300
resistor should be inserted
in series with the ground pin if negative supply voltage
transients are anticipated.
OPERATIO
U
The LTC1157 is a dual micropower MOSFET driver de-
signed specifically for operation at 3.3V and 5V and
includes the following functional blocks:
3.3V Logic Compatible Inputs
The LTC1157 inputs have been designed to accommodate
a wide range of 3.3V and 5V logic families. Approximately
50mV of hysteresis is provided to ensure clean switching.
An ultra low standby current voltage regulator provides
continuous bias for the logic-to-CMOS converter. The
logic-to-CMOS converter output enables the rest of the
circuitry. In this way the power consumption is kept to an
absolute minimum in the standby mode.
Gate Charge Pump
Gate drive for the power MOSFET is produced by an
internal charge pump circuit which generates a gate volt-
age substantially higher than the power supply voltage.
The charge pump capacitors are included on-chip and
therefore no external components are required to generate
the gate drive.
Controlled Gate Rise and Fall Times
When the input is switched ON and OFF, the gate is
charged by the internal charge pump and discharged in a
controlled manner. The charge and discharge rates have
been set to minimize RFI and EMI emissions.
BLOCK DIAGRA
W
(One Channel)
LOW STANDBY
CURRENT
REGULATOR
HIGH
FREQUENCY
OSCILLATOR
CHARGE
PUMP
LOGIC-TO-CMOS
CONVERTER
VOLTAGE
REGULATOR
INPUT
GND
V
S
GATE
GATE
DISCHARGE
LOGIC
LTC1157 BD
5
LTC1157
APPLICATIO S I FOR ATIO
W
U
U
U
MOSFET Selection
The LTC1157 is designed to operate with both standard
and logic level N-channel MOSFET switches. The choice of
switch is determined primarily by the operating supply
voltage.
Logic Level MOSFET Switches at 3.3V
Logic level switches should be used with the LTC1157
when powered from 2.7V to 4V. Although there is some
variation among manufacturers, logic level MOSFET
switches are typically rated with V
GS
= 4V with a maximum
continuous V
GS
rating of
10V. R
DS(ON)
and maximum
V
DS
ratings are similar to standard MOSFETs and there is
generally little price differential. Logic level MOSFETs are
frequently designated by an "L" and are usually available
in surface mount packaging. Some logic level MOSFETs
are rated up to
15V and can be used in applications which
require operation over the entire 2.7V to 5.5V range.
Standard MOSFET Switches at 5V
Standard N-channel MOSFET switches should be used
with the LTC1157 when powered from 4V to 5.5V supply
as the built-in charge pump produces ample gate drive to
fully enhance these switches when powered from a 5V
nominal supply. Standard N-channel MOSFET switches
are rated with V
GS
= 10V and are generally restricted to a
maximum of
20V.
Powering Large Capacitive Loads
Electrical subsystems in portable battery-powered equip-
ment are typically bypassed with large filter capacitors to
reduce supply transients and supply induced glitching. If
not properly powered however, these capacitors may
themselves become the source of supply glitching.
For example, if a 100
F capacitor is powered through a
switch with a slew rate of 0.1V/
s, the current during start-
up is:
I
START
= C(dV/dt)
= (100
10
6
) (1
10
5
)
= 10A
Obviously, this is too much current for the regulator (or
output capacitor) to supply and the output will glitch by as
much as a few volts.
The start-up current can be substantially reduced by
limiting the slew rate at the gate of an N-channel switch as
shown in Figure 1. The gate drive output of the LTC1157
is passed through a simple RC network, R1 and C1, which
substantially slows the slew rate of the MOSFET gate to
approximately 1.5
10
4
V/
s. Since the MOSFET is
operating as a source follower, the slew rate at the source
is essentially the same as that at the gate, reducing the
start-up current to approximately 15mA which is easily
managed by the system regulator. R2 is required to
eliminate the possibility of parasitic MOSFET oscillations
during switch transitions. Also, it is good practice to
isolate the gates of paralleled MOSFETs with 1k resistors
to decrease the possibility of interaction between switches.
Reverse Battery Protection
The LTC1157 can be protected against reverse battery
conditions by connecting a 300
resistor in series with
the ground pin. The resistor limits the supply current to
less than 12mA with 3.6V applied. Since the LTC1157
draws very little current while in normal operation, the
drop across the ground resistor is minimal. The 3.3V
P
(or control logic) can be protected by adding 10k resistors
in series with the input pins.
+
V
S
GND
G1
IN1
1/2 LTC1157
MTD3055EL
3.3
F
V
IN
LTC1157 TA02
LT1129-3.3
+
3.3V
LOAD
C1
0.1
F
C
LOAD
100
F
3.3V
R2
1k
R1
100k
ON/0FF
Figure 1. Powering a Large Capacitive Load
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