LTC3830EGN Linear Technology, LTC3830EGN Datasheet - Page 12

• Manufacturer Part Number: LTC3830EGN
• Description: IC DC/DC CONTRLR STEP-DWN 16SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC3830EGN

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 1
• Voltage - Output: 3.3V, Adj
• Current - Output: 20A
• Frequency - Switching: 200kHz
• Voltage - Input: 3 ~ 8 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

LTC3830/LTC3830-1
APPLICATIO S I FOR ATIO
Input Supply Considerations/Charge Pump
The 16-lead LTC3830 requires four supply voltages to
operate: V
MOSFET gate drive and a clean, low ripple V
LTC3830 internal circuitry (Figure 6). The LTC3830-1 and
the 8-lead LTC3830 have the PV
together inside the package (Figure 7). This pin, brought
out as V
as the 16-lead part, but must also be able to supply the gate
drive current to Q2.
In many applications, V
through an RC filter. This supply can be as low as 3V. The
low quiescent current (typically 800µA) allows the use of
relatively large filter resistors and correspondingly small
filter capacitors. 100Ω and 4.7µF usually provide ad-
equate filtering for V
4.7µF bypass capacitor as close to the LTC3830 V
possible.
Gate drive for the top N-channel MOSFET Q1 is supplied
from PV
power supply input) by at least one power MOSFET V
for efficient operation. An internal level shifter allows PV
to operate at voltages above V
mum. This higher voltage can be supplied with a separate
supply, or it can be generated using a charge pump.
Gate drive for the bottom MOSFET Q2 is provided through
PV
LTC3830-1 and the 8-lead LTC3830. This supply only
12
CC2
for the 16-lead LTC3830 or V
CC
CC1
IN
/PV
. This supply must be above V
for the main power input, PV
CC2
, has the same low ripple requirements
U
CC
. For best performance, connect the
CC
U
can be powered from V
CC
and V
CC2
10µF
D
12V
1N5242
W
Z
LTC3830
IN
and V
CC
CC1
, up to 14V maxi-
PV
1N5817
/PV
CC2
and PV
IN
CC
Figure 8. Tripling Charge Pump
CC2
U
CC
(the main
pins tied
PV
CC
1N5817
CC1
for the
for the
CC2
GS(ON)
pin as
G1
G2
CC1
for
IN
0.1µF
needs to be above the power MOSFET V
operation. PV
charge pump for the PV
lower supply to improve efficiency.
Figure 8 shows a tripling charge pump circuit that can be
used to provide 2V
top and bottom MOSFETs respectively. These should fully
enhance MOSFETs with 5V logic level thresholds. This
circuit provides 3V
2V
Schottky diodes. The circuit requires the use of Schottky
diodes to minimize forward drop across the diodes at
start-up. The tripling charge pump circuit can rectify any
ringing at the drain of Q2 and provide more than 3V
PV
to PGND to prevent transients from damaging the circuitry
at PV
The charge pump capacitors refresh when the G2 pin goes
high and the switch node is pulled low by Q2. The G2 on-
time becomes narrow when LTC3830 operates at maxi-
mum duty cycle (95% typical), which can occur if the input
supply rises more slowly than the soft-start capacitor or
the input voltage droops during load transients. If the G2
on-time gets so narrow that the switch node fails to pull
completely to ground, the charge pump voltage may
collapse or fail to start, causing excessive dissipation in
external MOSFET Q1. This is most likely with low V
voltages and high switching frequencies, coupled with
large external MOSFETs which slow the G2 and switch
node slew rates.
1N5817
0.1µF
IN
CC1
– 2V
CC1
; a 12V zener diode should be included from PV
V
IN
Q1
Q2
or the gate of Q1.
F
to PV
L
O
CC2
CC2
+
can also be driven from the same supply/
IN
IN
3830 F08
where V
C
OUT
– 3V
and 3V
V
OUT
CC1
F
, or it can be connected to a
to PV
F
IN
is the forward voltage of the
gate drive for the external
CC1
while Q1 is ON and
GS(ON)
for efficient
IN
3830fa
CC1
CC
at