Datasheet

3
LTC1872B
TYPICAL PERFORMANCE CHARACTERISTICS
U
W
Reference Voltage
vs Temperature
Undervoltage Lockout Trip
Voltage vs Temperature
Shutdown Threshold
vs Temperature
Maximum Current Sense Trip
Voltage vs Duty Cycle
Normalized Oscillator Frequency
vs Temperature
PIN FUNCTIONS
UUU
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. Nominal voltage range for this pin is
0.7V to 1.9V. Forcing this pin below 0.35V causes the
device to be shut down. In shutdown all functions are
disabled and the NGATE pin is held low.
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.
V
IN
(Pin 5): Supply Pin. Must be closely decoupled to GND
Pin 2.
NGATE (Pin 6): Gate Drive for the External N-Channel
MOSFET. This pin swings from 0V to V
IN
.
TEMPERATURE (°C)
–55
775
V
FB
VOLTAGE (mV)
780
790
795
800
825
810
–15
25
45 125
1872B G01
785
815
820
805
–35 5
65
85
105
V
IN
= 4.2V
TEMPERATURE (°C)
–55
–10
NORMALIZED FREQUENCY (%)
–8
–4
–2
0
10
4
–15
25
45 125
1872B G02
–6
6
8
2
–35 5
65
85
105
V
IN
= 4.2V
TEMPERATURE (°C)
–55
1.84
UVLO TRIP VOLTAGE (V)
1.88
1.96
2.00
2.04
2.24
2.12
–15
25
45 125
1872B G03
1.92
2.16
2.20
2.08
–35 5
65
85
105
V
IN
FALLING
DUTY CYCLE (%)
20 30
V
IN
– V
SENSE
– (mV)
100
187B2 G04
40 50
60 70
80 90
130
120
110
100
90
80
70
60
50
V
IN
= 4.2V
T
A
= 25°C
TEMPERATURE (
°C)
–55
200
I
TH
/RUN VOLTAGE (mV)
240
320
360
400
600
480
–15
25
45 125
1872B G05
280
520
560
440
–35 5
65
85
105
V
IN
= 4.2V