LCS700-708
Pin Functional Description
VCC Pin
IC power pin. In a typical application, VCC is connected to the
12 V system standby supply via a 5
W
resistor. This resistor
helps provide filtering and improves noise immunity.
Note: The system standby supply return should be connected to
the B- bus and not to the GROUND pin.
VREF Pin
3.4 VREF pin. An internal voltage reference network used as a
voltage source for FEEDBACK pin and DT/BF pin pull-up
resistor.
GROUND (G) Pin
G is the return node for all analog small signals. All small signal
pin bypass capacitors must be returned to this pin through short
traces, with the exception of the D-S high-voltage bypass
capacitor, and the VCCH bypass capacitor. It is internally
connected to the SOURCE pins to provide a star connection.
Do not connect the GROUND pin to the SOURCE pins,
nor to the B- bus, in the PCB layout.
OV/UV Pin
Overvoltage/Undervoltage pin. B+ is sensed by this pin through
a resistor divider. The OV/UV pin implements brown-in,
brown-out, and overvoltage lockout with hysteresis. Pulling this
pin down to ground will implement a remote-off function.
FEEDBACK (FB) Pin
Current fed into this pin determines LLC switching frequency;
higher current programs higher switching frequency. The pin
V-I characteristic resembles a diode to ground during normal
switching. An RC network between the VREF pin and
FEEDBACK pin determines the minimum operating frequency,
start-up frequency, soft-start time, and delay before start-up.
DEAD-TIME/BURST FREQUENCY (DT/BF) Pin
A resistor divider from VREF to ground programs dead-time,
maximum switching frequency at start-up, and burst-mode
threshold frequencies.
CURRENT-SENSE (IS) Pin
The CURRENT-SENSE pin is used for sensing transformer
primary current, to detect overload and fault conditions, through
a current sense resistor or a capacitive divider plus sense resistor
circuit. It resembles a reverse diode to ground, and does not
require a rectifier circuit for preventing negative pulses from
reaching the pin, provided the reverse current is limited to <5 mA.
Figure 3.
Pin Numbering and Designation.
H Package (eSIP-16C)
Exposed Metal
(On Package Edge)
1
Internally
Connected
VCCH
3 4 5 6 7 8 9 1011 13 14 16
S2
S1
NC
IS
DT/BF
FB
OV/UV
G
VREF
HB
G
G
VCCH
HB
D
NC
VCC
D
D
Exposed Pad
(Backside) Internally
Connected to GROUND
Pin (see eSIP-16C
Package Drawing)
PI-5636-051311
SOURCE (S1), (S2) Pins
SOURCE pins of internal low-side MOSFET. These should be
connected together on the PCB, and connected to the B- from
the PFC bulk capacitor or input high-voltage DC return.
HB Pin
This is the output of the half-bridge connected MOSFETs
(Source of high-side MOSFET, Drain of low-side MOSFET), to
be connected to the LLC power train (transformer primary and
series resonant capacitor).
VCCH Pin
Floating bootstrap supply pin for the LLC high-side driver. This
pin is referenced to the HB pin, which in turn is internally
connected to the SOURCE pin of the high-side MOSFET. A
bypass/storage capacitor between VCCH and HB pins, and a
boot strap diode with a series resistor from the standby supply,
are required. The storage capacitor is refreshed every time the
lower MOSFET turns on or its body diode conducts.
DRAIN (D) Pin
DRAIN pin of the internal high-side MOSFET. This connects to
the B+ from the PFC bulk capacitor or input high-voltage DC bus.
3
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Rev. B 062011
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