Datasheet

TPS78327
GND
EN
IN OUT
V
IN
V
OUT
1 Fm
1 Fm
4.2Vto5.5V 2.7V
On
Off
90
80
70
60
50
40
30
20
10
0
BatteryLife(Days)
5
10 20 30 40 50 60 70 80 90 100
DutyCycle(TimeinActiveMode)(%)
Battery,V =3.0V
TPS783,V =2.2V
CC
CC
TPS783xx
www.ti.com SBVS133 –FEBRUARY 2010
APPLICATION INFORMATION
X5R- and X7R-type capacitors are best because they
APPLICATION EXAMPLES
have minimal variation in value and ESR over
temperature. Maximum ESR should be less than
The TPS783 family of LDOs is factory-programmable
1.0Ω. With tolerance and dc bias effects, the
to have a fixed output. Note that during startup or
minimum capacitance to ensure stability is 1mF.
steady-state conditions, it is important that the EN pin
voltage never exceed V
IN
+ 0.3V.
EXTENDING BATTERY LIFE IN KEEP-ALIVE
CIRCUITRY APPLICATIONS FOR MSP430
AND OTHER LOW-POWER
MICROCONTROLLERS
One of the primary advantages of a low quiescent
current LDO is its extremely low energy requirement.
Counter-intuitively, this requirement enables a longer
battery life compared to using only the battery as an
unregulated voltage supply for low-power
microcontrollers such as the MSP430. Figure 19
illustrates the characteristic performance of an
unregulated (3.0V) battery supply versus a regulated
TPS783 supply for a typical MSP430 application.
Figure 18. Typical Application Circuit
INPUT AND OUTPUT CAPACITOR
REQUIREMENTS
Although an input capacitor is not required for
stability, it is good analog design practice to connect
a 0.1mF to 1.0mF low equivalent series resistance
(ESR) capacitor across the input supply near the
regulator. This capacitor counteracts reactive input
sources and improves transient response, noise
rejection, and ripple rejection. A higher-value
capacitor may be necessary if large, fast rise-time
load transients are anticipated, or if the device is not
located near the power source. If source impedance
is not sufficiently low, a 0.1mF input capacitor may be
necessary to ensure stability.
Calculated with an MSP430F model, operating at 6MHz.
The TPS783 series are designed to be stable with
Figure 19. Battery Life Comparison vs Duty Cycle
standard ceramic capacitors with values of 1.0mF or
for MSP430 Application
larger at the output.
Table 2 summarizes this comparison.
Table 2. Battery Life Comparison vs Active Mode Time for MSP430 Application
DUTY CYCLE TPS783xx BATTERY 1mA LDO
CONDITION/PERFORMANCE (%) (NO. OF DAYS) (NO. OF DAYS) (NO. OF DAYS)
Efficiency with V
BAT
= 3.0V and V
CC
= 2.2V (V
O
/V
I
) — 73% 100% 73%
LDO quiescent current (I
Q
) — 0.5mA 0 1mA
MSP430 active current — 2.19mA 3.09mA 2.19mA
MSP430 low-power current — 0.5mA 0.6mA 0.5mA
Active mode, 1 sec/hour 0.028 5742 6286 4373
Active mode, 10 sec/hour 0.28 1320 998 1085
Active mode, 100 sec/hour 2.8 151 106 148
Active mode, 1000 sec/hour 28 15.4 10.7 15.4
Active mode, 100% duty cycle (on all the time) 100 4.2 3.0 4.2
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