Datasheet
7
LTC3830/LTC3830-1
3830fa
UU
U
PI FU CTIO S
FREQSET (Pin 11/NA/NA): Frequency Set. Use this pin to
adjust the free-running frequency of the internal oscillator.
With the pin floating, the oscillator runs at about 200kHz.
A resistor from FREQSET to ground speeds up the oscil-
lator; a resistor to V
CC
slows it down.
I
MAX
(Pin 12/NA/NA): Current Limit Threshold Set. I
MAX
sets the threshold for the internal current limit compara-
tor. If I
FB
drops below I
MAX
with G1 on, the LTC3830 goes
into current limit. I
MAX
has an internal 12µA pull-down to
GND. Connect this pin to the main V
IN
supply at the drain
of Q1, through an external resistor to set the current limit
threshold. Connect a 0.1µF decoupling capacitor across
this resistor to filter switching noise.
I
FB
(Pin 13/NA/NA): Current Limit Sense. Connect this pin
to the switching node at the source of Q1 and the drain of
Q2 through a 1k resistor. The 1k resistor is required to
prevent voltage transients from damaging I
FB
.This pin is
used for sensing the voltage drop across the upper
N-channel MOSFET, Q1.
V
CC
(Pin 14/Pin 7/Pin 7): Power Supply Input. All low
power internal circuits draw their supply from this pin.
Connect this pin to a clean power supply, separate from
the main V
IN
supply at the drain of Q1. This pin requires a
4.7µF bypass capacitor. The LTC3830-1 and the 8-lead
LTC3830 have V
CC
and PV
CC2
tied together at Pin 7 and
require a 10µF bypass capacitor to GND.
PV
CC2
(Pin 15/Pin 7/Pin 7): Power Supply Input for G2.
Connect this pin to the main high power supply.
G2 (Pin 16/Pin 8/Pin 8): Bottom Gate Driver Output.
Connect this pin to the gate of the lower N-channel
MOSFET, Q2. This output swings from PGND to PV
CC2
. It
remains low when G1 is high or during shutdown mode.
To prevent output undershoot during a soft-start cycle, G2
is held low until G1 first goes high. (FFBG in Block
Diagram.)
BLOCK DIAGRA
W
–
+
–
+
–
+
R
S
PV
CC1
G1
PV
CC2
G2
PGND
FB
SENSE
+
V
REF
V
REF
– 3%
V
REF
+ 3%
18k
11.2k
SENSE
–
3830 BD
BG
Q
Q
RPOR
FFBG
ENABLE
G2
SQ
–
+
PWM
QSS
V
REF
V
REF
– 3% V
REF
+ 3%
MAXMINERR
12µA
INTERNAL
OSCILLATOR
100ms DELAY
SHDN
FREQSET
COMP
SS
POWER DOWN
DISDR
LOGIC AND
THERMAL SHUTDOWN
QC
DISABLE
ILIM
2.2V
+
–
CC
12µA
I
MAX
I
FB
–
+
V
V
CC1
+ 2.5V
PV
CC1
1.2V