4
LTC1538-AUX/LTC1539
ELECTRICAL CHARACTERISTICS
T
A
= 25°C, V
IN
= 15V, V
RUN/SS1,2
= 5V unless otherwise noted.
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
Low-Battery Comparator
V
SATLBO
LBO Saturation Voltage I
LBO
= 1.6mA, V
LBI
= 1.1V 0.6 1 V
I
LLBO
LBO Leakage V
LBO
= 12V, V
LBI
= 1.4V ● 0.01 1 µA
V
THLB1
LBI Trip Voltage High to Low Transition on LBO ● 1.16 1.19 1.22 V
I
INLB1
LBI Input Current V
LBI
= 1.19V ● 150 nA
V
HYSLBO
LBO Hysteresis 20 mV
Auxiliary Regulator/Comparator
I
AUXDR
AUXDR Current V
EXTVCC
= 0V
Max Current Sinking Capability V
AUXDR
= 4V, V
AUXFB
= 1.0V, V
AUXON
= 5V 10 15 mA
Control Current V
AUXDR
= 5V, V
AUXFB
= 1.5V, V
AUXON
= 5V 1 5 µA
Leakage when OFF V
AUXDR
= 24V, V
AUXFB
= 1.5V, V
AUXON
= 0V 0.01 1 µA
I
INAUXFB
AUXFB Input Current V
AUXFB
= 1.19V, V
AUXON
= 5V 0.01 1 µA
I
INAUXON
AUXON Input Current V
AUXON
= 5V 0.01 1 µA
V
THAUXON
AUXON Trip Voltage V
AUXDR
= 4V, V
AUXFB
= 1V 1.0 1.19 1.4 V
V
SATAUXDR
AUXDR Saturation Voltage I
AUXDR
= 1.6mA, V
AUXFB
= 1V, V
AUXON
= 5V 0.4 0.8 V
V
AUXFB
AUXFB Voltage V
AUXON
= 5V, 11V < V
AUXDR
< 24V (Note 5) ● 11.5 12.00 12.5 V
V
AUXON
= 5V, 3V < V
AUXDR
< 7V ● 1.14 1.19 1.24 V
V
THAUXDR
AUXFB Divider Disconnect Voltage V
AUXON
= 5V (Note 5); Ramping Negative 7.5 8.5 9.5 V
The ● denotes specifications which apply over the full operating
temperature range.
Note 1: T
J
is calculated from the ambient temperature T
A
and power
dissipation P
D
according to the following formulas:
LTC1538CG-AUX: T
J
= T
A
+ (P
D
)(95°C/W)
LTC1539CGW: T
J
= T
A
+ (P
D
)(85°C/W)
Note 2: The LTC1538-AUX and LTC1539 are tested in a feedback loop
which servos V
OSENSE1,2
to the balance point for the error amplifier
(V
ITH1,2
= 1.19V).
Note 3: Dynamic supply current is higher due to the gate charge being
delivered at the switching frequency. See Applications Information.
Note 4: Oscillator frequency is tested by measuring the C
OSC
charge and
discharge current (I
OSC
) and applying the formula:
f
OSC
(kHz) = 8.4(10
8
)[C
OSC
(pF) + 11]
-1
(1/I
CHG
+ 1/I
DISC
)
–1
Note 5: The auxiliary regulator is tested in a feedback loop which servos
V
AUXFB
to the balance point for the error amplifier. For applications with
V
AUXDR
> 9.5V, V
AUXFB
uses an internal resistive divider. See Applications
Information section.
