Application Hint 9 Micrel
5-216 1997
Load
MIC5014
Control Input
OFF
ON
1
2
3
4
8
7
6
5
+2.75V to +30V
NC
GateGnd
Source
Input
V+
NC
NC
1µF
100nF
1N4001 (2)
1N5817
1RF540
Introduction
The current trend for more efficient use of power has led to
a new standard in logic based systems: the use of 3.3V logic
as opposed to 5V logic. Efficient power management is
especially important in battery based systems such as
portable laptop/notebook PCs and cellular phones where
maximum use time is determined by battery life. The
MIC5014 family has a minimum required supply rail of
2.75V, which is the lowest required voltage of any high
side driver in the industry! This makes the MIC5014
family ideal for use in any low voltage environment where
power switching is necessary. This note briefly describes
the characteristics of these devices at low voltages, and
shows several example applications where the low voltage
feature is used.
Typical Parameters at V+ = 3.3V
Table I shows the typical parameters expected at a 3.3V
supply voltage. At 15µA quiescent current and 35µA oper-
ating current, we offer very little battery drain at this voltage.
Also worthy of attention is the fact that these devices offer
a full 4.5V gate enhancement with a supply voltage of only
3.0V! Perhaps the only drawback is the rise time at these
low voltages, which is on the order of 35 to 40ms. For most
power switching applications in this voltage range,
Table 1: Typical Parameters at V+ = 3.3V
Application Hint 9
Low Voltage Operation of the MIC5014 Family
by Brenda Kovacevic
this has not been seen to present difficulties and is a small
price to pay for the greatly lowered battery drain. If faster
switching speeds are desired, the rise time can be improved
to 20 to 30ms by bootstrapping off the positive supply, as
shown in figure 1. Faster times than this can be attained by
increasing the size of the bootstrap capacitor at the ex-
pense of the additional space required. Fall times remain on
the order of 6 to10µs.
Parameter T ypical Value Units
Supply Current,Off State 15 µA
Supply Current,On State 35 µA
High Side Turn-On Time 35 ms
(CL = 1300 pF)
Turn-Off Time 6 µs
Gate Enhancement 4.5 V
(VGATE - VSUPPLY)
Logic Input Current 1 µA
(High State)
Figure 1. Low Voltage Bootstrapped High
Side Switch
1997 5-217
Application Hint 9 Micrel
5
Typical Low Voltage Applications
Sleep Mode Switching
One commonly employed technique for extending battery
life is the use of a "sleep mode" switch, in which the
microprocessor shuts down all the functions that represent
power drain after a preset time of nonuse while maintaining
the system memory. This type of a switch must typically be
a high side switch, or a switch that controls the availabllity
of the positive supply, as standard computer or logic based
systems often have common ground busses and /or shield-
ing.
The MIC5016 plus two logic level FETs make an ideal dual
sleep mode switch (figure 2) without the bulk and unreliability
of relays or the voltage drop of bipolar transistors (See
Application Hint 5 for more information plus a board layout
for sleep mode switching with regards to our MIC5011 high
side driver).
A logic level FET is very similar to a regular power FET
except for the threshold voltage requirements, which are
VGS = 4 V for turn-on and 5 V for full enhancement. A
regular power FET would require a minimum of 10V for full
enhancement. This feature makes the logic level FET ideal
for this kind of switching. The only drawback it has is that
it's gate cannot withstand more than 10V of enhancement.
The MIC5014/5016 devices are equipped with an internal
zener clamp, but at 15V it will not save us here! We
recommend that an external zener clamp or regular power
FET be used if a supply higher than 4V is required.
As the MIC5014 is pin to pin compatible with the MIC5011,
the board layout for a single sleep mode switch as featured
in Application Hint 5 will also work for the MIC5014.
Low Battery Sense and Disconnect
When a battery is discharged to the point that the load goes
significantly out of regulation, it is often beneficial to discon-
nect the load from the battery to prevent further discharge.
In the case of NiCd or NiMH batteries, repeated deep
discharging has a negative impact on battery life. A simple
scheme can be formulated using the MIC2951 super low
drop out regulator to generate a well regulated 3.3V supply
from four 1.2V battery cells. When the output drops to below
5% of the rated value, the ERROR flag goes low, pulling
down the RESETof the latch which shuts down the control
input to the MIC5014. This turns off the MOSFET switch
connecting the battery to the regulator. It is important to
hold the SET input to the latch low for 30 to 40ms on start-
up to allow the regulator to kick in. This output can also be
fed to a microcontroller, signalling the user that it is time to
charge his batteries.
Although it is possible to use feedback from the ERROR
output to the shutdown input of the MIC2951 to perform this
function, the addition of the MIC5014 and FET switch
results in less current drain (20 to 25µA extra for the
MIC5014 plus latch as opposed to the current required to
bias and drive a bipolar transistor). It also allows the
MIC2951 to act as the central controlling point for shutdown
in applications where the unregulated battery voltage is fed
to other subsystems, such as an SMPS converter, in
addition to the MIC2951.
Figure 2: 3 to 4 V Dual Sleep Mode
Switch
Figure 3: Low Battery Shutdown Switch
MIC5014
1
2
3
4
8
7
6
5IRLZ24
VBATT = +3.6V to +4.8V
NC
GateGnd
Source
Input
V+
NC
NC
SQ
R
1/2
SN54COO
configured as
a latch
3.3µF
300k
1%
100pF
180k
1%
3.3µF
VCC OUT
(+3.3V)
SD
ERROR
GND FB
VOUT
+ VIN
47
1
8
3
ON OFF
SHUTDOWN
INPUT
1N754
6.8V
10µF
V+
VBATT
100k
Logic
MIC5016BN
OFF
ON
12
10
14
11
4
2
6
5
IRLZ24
+3V to +4V
Gate A
Source B
Gnd
In A
V+ B
V+ A
Source A
Gate B
10µF
3In B
Peri-
pherals
IRLZ24