Datasheet

Absolute Maximum Ratings (Note 1)
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
Supply Voltage (V
IN
to GND or GND
to OUT) + 5.8V
SD
(GND − 0.3V) to
(V
IN
+ 0.3V)
V
NEG
and V
OUT
Continuous Output
Current 10mA
V
OUT
Short-Circuit Duration to GND
(Note 2) 1 sec.
Continuous Power Dissipation (T
A
=
25˚C) (Note 3) 600mW
T
JMAX
(Note 3) 150˚C
θ
JA
(Note 3) 250˚C/W
Operating Input Voltage Range 2.7V to 5.5V
Operating Output Current Range 0mA to 10mA
Operating Ambient −40˚C to 85˚C
Temp. Range
Operating Junction Temp. Range −40˚C to 110˚C
Storage Temperature −65˚C to 150˚C
Lead Temp. (Soldering, 10 sec.) 300˚C
ESD Rating (Note 4) 2kV
Electrical Characteristics
Limits with standard typeface apply for T
J
= 25˚C, and limits in boldface type apply over the full temperature range. Unless
otherwise specified V
IN
= 3.6V, C
1
=C
2
= 1µF, C
3
= 10µF.
Symbol Parameter Conditions Min Typ Max Units
I
Q
Supply Current Open Circuit, No Load 500 950 µA
I
SD
Shutdown Supply Current 0.05 1 µA
F
SW
Switching Frequency
(Note 5)
2.7V ≤ V
IN
≤.5.5V
V
IN
= 3.6V
50
60
110
105
180
170
kHz
η
POWER
Power Efficiency at V
NEG
I
L
= 3.6mA
I
L
= 10mA
94
91
%
T
START
Start Up time (Note 6) 120 600 µs
R
NEG
Output Resistance to V
NEG
(Note 7) 30 Ω
V
R
Output Voltage Ripple
(Note 8)
I
L
=2.5mA, V
OUT
= −2.7V
I
L
= 10mA, V
OUT
= −3.8V
1
2
mV
V
FB
Feedback Pin Reference
Voltage
I
L
= 2.5mA (Note 9) −1.25 −1.20 −1.15 V
V
OUT
Adjustable Output Voltage 5.5V ≥ V
IN
≥ 2.7V, 2.5mA ≥ I
L
5.5V ≥ V
IN
≥ 3.0V, 10mA ≥ I
L
≥
0mA
−(V
IN
−0.3V)
−(V
IN
−1.2V)
V
Load Regulation 0 to 10mA, V
OUT
= − 2.4V 5 mV/mA
Line Regulation 5.5V ≥ V
IN
≥ 2.7V, I
L
= 2.5mA 1 mV/V
V
IH
Shutdown Pin Input Voltage
High
5.5V ≥ V
IN
≥ 2.7V 2.2 V
V
IL
Shutdown Pin Input Voltage
Low
5.5V ≥ V
IN
≥ 2.7V 0.5 V
Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Electrical specifications do not apply when operating the device
beyond its rated operating conditions.
Note 2: OUT may be shorted to GND for one second without damage. However, shorting OUT to V
IN
may damage the device and must be avoided. Also, for
temperatures above T
A
= 85˚C, OUT must not be shorted to GND or V
IN
or device may be damaged.
Note 3: The maximum power dissipation must be de-rated at elevated temperatures and is limited by T
JMAX
(maximum junction temperature), T
A
(ambient
temperature) and θ
JA
(junction-to-ambient thermal resistance). The maximum power dissipation at any temperature is:
PDiss
MAX
=(T
JMAX
—T
A
)/θ
JA
up to the value listed in the Absolute Maximum Ratings.
Note 4: Rating is for the human body model, a 100pF capacitor discharged through a 1.5 kΩ resistor into each pin.
Note 5: The output switches operate at one half the oscillator frequency, f
OSC
=2f
SW
.
Note 6: All capacitors are 1µF.
Note 7: Current drawn from V
NEG
pin decreases power efficiency and will increase output voltage ripple.
Note 8: In the test circuit, capacitors C
1
and C
2
are 1µF, C
3
= 10µF, 0.30Ω maximum ESR capacitors. Capacitors with higher ESR will increase output resistance,
increase output voltage ripple, and reduce efficiency.
Note 9: The feedback resistors R1 and R2 are 200kΩ resistors.
LM2687
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