LTC3855 LINER [Linear Technology], LTC3855 Datasheet - Page 7

• Manufacturer Part Number: LTC3855
• Description: Dual, Fast, Accurate Step-Down DC/DC Controller
• Manufacturer: LINER [Linear Technology]

TYPICAL PERFORMANCE CHARACTERISTICS
TRACK/SS1
200mV/DIV
500mV/DIV
AC-COUPLED
100mV/DIV
CLKOUT
10V/DIV
10V/DIV
5V/DIV
5V/DIV
5V/DIV
PLLIN
RUN1
V
SW1
SW2
5A/DIV
OUT
V
OUT
I
FIGURE 19 CIRCUIT
V
V
LOAD = 0A
MODE/PLLIN = 333kHz EXTERNAL CLOCK
Regular Soft Start-Up
C
V
V
FORCED CONTINUOUS MODE
FIGURE 17 CIRCUIT, CHANNEL 1, V
Phase Relationship:
PHASMD = Ground
L
IN
OUT1
SS
IN
OUT
Overcurrent Protection
V
V
FORCED CONTINUOUS MODE
CURRENT LIMIT = 17A
OVERLOAD = 7.5A TO 17.5A
FIGURE 17 CIRCUIT, CHANNEL 1, V
= 12V
= 12V
IN
OUT
= 10nF
= 1.2V
= 12V
= 5V, V
= 1.2V
0°
THAN HALF OF REGULATED
OUT2
60°
FULL CURRENT LIMIT
WHEN V
500ns/DIV
= 3.3V
1ms/DIV
5ms/DIV
180°
OUT
HIGHER
RNG1
RNG1
= SGND
3838 G15
3838 G09
= SGND
3838 G12
TRACK/SS1
500mV/DIV
200mV/DIV
TRIGGER
CIRCUIT
10A/DIV
SHORT-
CLKOUT
1V/DIV
10V/DIV
10V/DIV
5V/DIV
5V/DIV
5V/DIV
V
PLLIN
RUN1
V
OUT
SW1
SW2
OUT
I
L
V
V
I
FIGURE 17 CIRCUIT, CHANNEL 1, V
Short-Circuit Protection
LOAD
FIGURE 19 CIRCUIT
V
V
LOAD = 0A
MODE/PLLIN = 333kHz EXTERNAL CLOCK
C
V
V
V
FIGURE 17 CIRCUIT, CHANNEL 1, V
IN
OUT
Soft Start-Up Into
Pre-Biased Output
CURRENT LIMIT STARTS TO FOLD BACK AS
Phase Relationship:
PHASMD = Float
V
SS
IN
OUT
OUT
IN
OUT1
OUT
= 12V
= 12V
= 12V
= 10nF
= 1.2V
= 0A
= 1.2V
PRE-BIASED TO 0.75V
DROPS BELOW HALF OF REGULATED
= 5V, V
0°
OUT2
90°
500μs/DIV
500ns/DIV
= 3.3V
1ms/DIV
180°
C
RECHARGE
RNG1
RNG1
OUT
= SGND
3838 G13
= SGND
3838 G10
3838 G15
AC-COUPLED
100mV/DIV
TRACK/SS1
200mV/DIV
500mV/DIV
10A/DIV
CLKOUT
5V/DIV
10V/DIV
10V/DIV
5V/DIV
5V/DIV
V
PLLIN
BG1
V
OUT
SW1
SW2
OUT
I
L
V
V
FORCED CONTINUOUS
MODE
I
FIGURE 17 CIRCUIT, CHANNEL 1, V
Overvoltage Protection
LOAD
V
V
FORCED CONTINUOUS MODE
FIGURE 17 CIRCUIT, CHANNEL 1, V
IN
OUT
Phase Relationship:
PHASMD = INTV
FIGURE 19 CIRCUIT
V
V
LOAD = 0A
MODE/PLLIN = 333kHz EXTERNAL CLOCK
Output Tracking
IN
OUT
IN
OUT1
= 12V
OVERVOLTAGE CREATED BY APPLYING
= 12V
= 12V
= 1.2V
= 0A
= 1.2V
A CHARGED CAPACITOR TO V
= 5V, V
0°
OUT2
20μs/DIV
500ns/DIV
10ms/DIV
= 3.3V
120°
LTC3838
CC
BG STAYS ON UNTIL
V
BELOW OVERVOLTAGE
THRESHOLD
OUT
240°
IS PULLED
RNG1
RNG1
OUT
= SGND
3838 G14
= SGND
3838fa
7
3838 G11
3838 G17