LTC1174
LTC1174-3.3/LTC1174-5
W U U
U
APPLICATIO S I FOR ATIO
V
OUT
LTC1174-5 regulator and also to one or more loads in
parallel with the the regulator’s VIN. If the battery is dis-
connected while the LTC1174/LTC1174-3.3/LTC1174-5
regulator is supplying a light load and one of the parallel
circuitsisaheavyload,theinputcapacitoroftheLTC1174/
LTC1174-3.3/LTC1174-5regulatorcouldbepulleddown
faster than the output capacitor, causing the absolute
maximum ratings to be exceeded. The result is often a
latchup which can be destructive if VIN is reapplied. Bat-
terydisconnectispossibleasaresultofmechanicalstress,
bad battery contacts or use of a lithium-ion battery with
a built-in internal disconnect. The user needs to assess
his/her application to determine whether this situation
could occur. If so, additional protection is necessary.
6.8nF**
R2
R1
1
LTC1174
V
FB
100pF*
ADJUSTABLE APPLICATIONS
LOW NOISE APPLICATIONS
*
1174 F04
**
Figure 4. LTC1174 Adjustable Configuration
INPUT VOLTAGE
4V TO 12V
47µF*
+
6
16V
0.1µF
V
IN
×2
3
2
7
8
1
5
LB
LB
SHUTDOWN
IN
Prevention against latchup can be accomplished by sim-
ply connecting a Schottky diode across the SW and VIN
pins as shown in Figure 6. The diode will normally be
reverse biased unless VIN is pulled below VOUT at which
time the diode will clamp the (VOUT – VIN) potential to less
than the 0.6V required for latchup. Note that a low leakage
Schottky should be used to minimize the effect on no-load
supplycurrent.SchottkydiodessuchasMBR0530,BAS85
and BAT84 work well. Another more serious effect of the
protection diode leakage is that at no load with nothing to
provide a sink for this leakage current, the output voltage
can potentially float above the maximum allowable toler-
ance. To prevent this from occuring, a resistor must be
connected between VOUT and ground with a value low
enough to sink the maximum possible leakage current.
V
OUT
OUT
SW
I
PGM
50µH**
LTC1174HV-5
GND
+
47µF*
16V
×2
MBRS140T3
4
V
OUT
–5V
45mA
1174 F05
AVX TPSD476K016
COILTRONICS CTX50-4
*
**
Figure 5. Positive-to-Negative 5V Converter
output voltage is now taken off the GND pin. Therefore,
the maximum input voltage is now determined by the
differencebetweentheabsolutemaximumvoltagerating
and the output voltage. A maximum of 12V is specified in
Figure5,givingthecircuita1.5VofheadroomforVIN.Note
that the circuit can operate from a minimum of 4V, making
it ideal for a 4 NiCad cell application. For a higher output
current circuit, please refer to the Typical Applications
section.
LATCHUP
PROTECTION
SCHOTTKY
Absolute Maximum Ratings and Latchup Prevention
V
V
SW
LTC1174
OUT
IN
TheabsolutemaximumratingsspecifythatSW(Pin5)can
neverexceedVIN (Pin6)bymorethan0.3V.Normallythis
situation should never occur. It could, however, if the
output is held up while the supply is pulled down. A con-
ditionwherethiscouldpotentiallyoccuriswhenabattery
is supplying power to an LTC1174/LTC1174-3.3/
+
LTC1174-3.3
LTC1174-5
1174 F06
Figure 6. Preventing Absolute Maximum
Ratings from Being Exceeded
1174fe
10
Linear Systems [ Linear Systems ]
