LTC1704 Linear Technology, LTC1704 Datasheet - Page 8

• Manufacturer Part Number: LTC1704
• Description: 550kHz Synchronous Switching Regulator Controller Plus Linear Regulator Controller
• Manufacturer: Linear Technology

PI FU CTIO S
LTC1704/LTC1704B
compensation and soft-start connections should return to
GND. GND and PGND should connect only at a single
point, near the PGND pin and the negative plate of the V
bypass capacitor.
REGFB (Pin 9): Linear Regulator Controller Feedback
Input. REGFB should be connected through a resistor
divider network to V
linear regulator.
REGILM (Pin 10): Linear Regulator Controller Current
Limit Setting cum ON/OFF Control. This pin is internally
servoed to 0.8V. An external resistor R
and REGILM programs the REGILM pin input current. This
current determines the maximum pass transistor base
current and directly controls the linear regulator current
sourcing capabilitiy. An external capacitor, C
to this pin to control the turn-on time of the linear regula-
tor, the minimum value for this capacitor is 100pF. Refer
to the Linear Regulator Current Limit Programming sec-
tion for more information on choosing R
Pulling REGILM to GND turns off the linear regulator. If
both RUN/SS and REGILM are pulled low, the LTC1704
enters shutdown mode.
V
except the switcher output drivers are powered from this
pin. V
should be bypassed to GND with at least a 10 F capacitor
in close proximity to the LTC1704.
TEST CIRCUIT
8
CC
U
(Pin 11): Power Supply Input. All internal circuits
CC
should be connected to a low noise 5V supply, and
U
OUTREG
U
f
OSC
V
FB
2000pF
to set the output voltage of the
100
1 F
2k
REGILM
REGILM
1
2
3
4
5
6
7
8
DELAY
TG
SW
I
RUN/SS
COMP
FB
REGDR
GND
MAX
between V
and C
LTC1704
is added
250k
DELAY
REGILM
PGOOD
BOOST
REGFB
PGND
CC
PV
IN
V
BG
.
CC
CC
16
15
14
13
12
11
10
9
PGOOD (Pin 12): Power Good. PGOOD is an open-drain
logic output. PGOOD pulls low if any of the two supply
outputs are outside 10% of their nominal levels. An
external pull-up resistor is required at PGOOD to allow it
to swing positive.
PGND (Pin 13): Power Ground. The BG driver returns to
this pin. Connect PGND to a high current ground node in
close proximity to the sources of external MOSFET QB,
and the V
BG (Pin 14): Switcher Controller Bottom Gate Drive. The
BG pin drives the gate of the bottom N-channel synchro-
nous switch MOSFET, QB. BG is designed to typically drive
up to 10,000pF of gate capacitance.
PV
ply. PV
must be connected to a voltage high enough to fully turn
on the external MOSFET, QB. PV
nected directly to V
requires at least a 10 F bypass capacitor directly to PGND.
BOOST (Pin 16): Switcher Controller Top Gate Driver
Supply. The BOOST pin supplies power to the floating TG
driver. Bypass BOOST to SW with a 1 F capacitor. An
external Schottky diode from V
complete floating charge-pumped supply at BOOST. No
other external supplies are required.
CC
I
(Pin 15): Switcher Controller Bottom Gate Driver Sup-
BOOST
2000pF
80k
CC
IN
provides power to the BG output driver. PV
I
and V
PVCC
OUTSW
I
VCC
IN
, the main system 5V supply. PV
R
100k
1704 TC
+
REGILM
100pF
bypass capacitors.
10 F
CC
5V
IN
should generally be con-
to BOOST creates a
1704bfa
CC
CC