Datasheet

3
LTC1779
Reference Voltage
vs Temperature
Undervoltage Lockout Trip
Voltage vs Temperature
Shutdown Threshold
vs Temperature
Normalized Oscillator Frequency
vs Temperature
I
TH
/RUN (Pin 1): This pin performs two functions. It
serves as the error amplifier compensation point as well as
the run control input. The current comparator threshold
increases with this control voltage. Nominal voltage range
for this pin is 0.7V to 1.9V. Forcing this pin below 0.325V
causes the device to be shut down. In shutdown all
functions are disabled and the internal P-channel MOSFET
is turned off. The SW pin will be high impedance.
GND (Pin 2): Ground Pin.
V
FB
(Pin 3): Receives the feedback voltage from an exter-
nal resistive divider across the output.
SENSE
–
(Pin 4): The Negative Input to the Current Com-
parator. Can be connected to V
IN
for default minimum
peak current of 250mA. Connecting a resistor between
SENSE
–
and V
IN
specifies a lower peak current. (See
Applications Information for specifying resistor value.)
V
IN
(Pin 5): Supply Pin. Must be closely decoupled to GND
Pin 2.
SW (Pin 6): Switching Node and Drain of Internal
P-Channel Power MOSFET. Connects to external induc-
tor and catch diode.
TEMPERATURE (°C)
–55
775
V
FB
VOLTAGE (mV)
780
790
795
800
825
810
–15
25
45 125
1779 G01
785
815
820
805
–35 5
65
85
105
V
IN
= 4.2V
TEMPERATURE (°C)
–55
–15
NORMALIZED FREQUENCY (%)
–12
–6
–3
0
15
6
–15
25
45 125
1779 G02
–9
9
12
3
–35 5
65
85
105
V
IN
= 4.2V
TEMPERATURE (°C)
–55
1.84
1.80
TRIP VOLTAGE (V)
1.88
1.96
2.00
2.20
2.08
–15
25
45 125
1779 G03
1.92
2.12
2.16
2.04
–35 5
65
85
105
V
IN
FALLING
TEMPERATURE (°C)
–55
200
I
TH
/RUN VOLTAGE (mV)
240
320
360
400
600
480
–15
25
45 125
1779 G04
280
520
560
440
–35 5
65
85
105
V
IN
= 4.2V
INPUT VOLTAGE (V)
2
0.35
R
DS(ON)
(Ω)
0.50
0.80
0.95
1.10
1.85
1.40
4
6
7
1779 G05
0.65
1.55
1.70
1.25
35
8
9
10
T
A
= 125°C
T
A
= 25°C
T
A
= –55°C
I
SW
= 100mA
SENSE
–
= V
IN
R
DS(ON)
of Internal P-Channel FET
vs Input Voltage
TYPICAL PERFOR A CE CHARACTERISTICS
UW
UU
U
PI FU CTIO S
R
DS(ON)
of Internal P-Channel FET
vs Temperature
TEMPERATURE (°C)
–55
0.35
R
DS(ON)
(Ω)
0.50
0.80
0.95
1.10
1.85
1.40
5–15
45
65
1779 G06
0.65
1.55
1.70
1.25
–35 25
85
105
125
I
SW
= 100mA
SENSE
–
= V
IN
V
IN
= 2.4V
V
IN
= 4.2V
V
IN
= 9.8V
V
IN
= 8.4V
V
IN
= 6V