Datasheet

LTC3857
3
3857fd
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
LOADREG
Output Voltage Load Regulation (Note 4)
Measured in Servo Loop,
∆I
TH
Voltage = 1.2V to 0.7V
l
0.01 0.1 %
(Note 4)
Measured in Servo Loop,
∆I
TH
Voltage = 1.2V to 2V
l
–0.01 –0.1 %
g
m1,2
Transconductance Amplifier g
m
(Note 4) I
TH1, 2
= 1.2V, Sink/Source = 5µA 2 mmho
I
Q
Input DC Supply Current (Note 5)
Pulse-Skipping or Forced Continuous
Mode (One Channel On)
RUN1 = 5V and RUN2 = 0V, V
FB1
= 0.83V(No Load) or
RUN1 = 0V and RUN2 = 5V, V
FB2
= 0.83V(No Load)
1.3 mA
Pulse-Skipping or Forced Continuous
Mode (Both Channels On)
RUN1, 2 = 5V, V
FB1,2
= 0.83V (No Load) 2 mA
Sleep Mode (One Channel On) RUN1 = 5V and RUN2 = 0V, V
FB1
= 0.83V(No Load) or
RUN1 = 0V and RUN2 = 5V, V
FB2
= 0.83V(No Load)
50 75 µA
Sleep Mode (Both Channels On) RUN1, 2 = 5V, V
FB1,2
= 0.83V (No Load) 65 120 µA
Shutdown RUN1, 2 = 0V 8 20 µA
UVLO Undervoltage Lockout INTV
CC
Ramping Up
INTV
CC
Ramping Down
l
l
3.6
4.0
3.8
4.2
4
V
V
V
OVL
Feedback Overvoltage Protection Measured at V
FB1,2
, Relative to Regulated V
FB1,2
71013 %
I
SENSE
+
SENSE
+
Pin Current Each Channel ±1 µA
I
SENSE
–
SENSE
–
Pins Current Each Channel
V
SENSE
–
< INTV
CC
– 0.5V
V
SENSE
–
> INTV
CC
+ 0.5V 550
±1
950
µA
µA
DF
MAX
Maximum Duty Factor In Dropout, FREQ = 0V 98 99.4 %
I
TRACK/SS1,2
Soft-Start Charge Current V
TRACK1,2
= 0V 0.7 1 1.4 µA
V
RUN1,2
On RUN Pin On Threshold V
RUN1
, V
RUN2
Rising
l
1.21 1.26 1.31 V
V
RUN1,2
Hyst RUN Pin Hysteresis 50 mV
V
SENSE(MAX)
Maximum Current Sense Threshold V
FB1,2
= 0.7V, V
SENSE1
–,
2
– = 3.3V, I
LIM
= 0
V
FB1,2
= 0.7V, V
SENSE1
–,
2
– = 3.3V, I
LIM
= FLOAT
V
FB1,2
= 0.7V, V
SENSE1
–,
2
– = 3.3V, I
LIM
= INTV
CC
l
l
l
22
43
64
30
50
75
36
57
85
mV
mV
mV
Gate Driver
TG1,2 Pull-Up On-Resistance
Pull-Down On-Resistance
2.5
1.5


BG1,2 Pull-Up On-Resistance
Pull-Down On-Resistance
2.4
1.1


TG1,2 t
r
TG1,2 t
f
TG Transition Time:
Rise Time
Fall Time
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
25
16
ns
ns
BG1,2 t
r
BG1,2 t
f
BG Transition Time:
Rise Time
Fall Time
(Note 6)
C
LOAD
= 3300pF
C
LOAD
= 3300pF
28
13
ns
ns
TG/BG t
1D
Top Gate Off to Bottom Gate On Delay
Synchronous Switch-On Delay Time
C
LOAD
= 3300pF Each Driver 30 ns
BG/TG t
1D
Bottom Gate Off to Top Gate On Delay
Top Switch-On Delay Time
C
LOAD
= 3300pF Each Driver 30 ns
t
ON(MIN)
Minimum On-Time (Note 7) 95 ns
ELECTRICAL CHARACTERISTICS
The l denotes the specifications which apply over the full operating junction
temperature range, otherwise specifications are at T
A
= 25°C (Note 2). V
IN
= 12V, V
RUN1,2
= 5V, EXTV
CC
= 0V, unless otherwise noted.