LM5642MH NSC [National Semiconductor], LM5642MH Datasheet - Page 2

• Manufacturer Part Number: LM5642MH
• Description: High Voltage, Dual Synchronous Buck Converter with Oscillator Synchronization
• Manufacturer: NSC [National Semiconductor]

www.national.com
Connection Diagrams
Ordering Information
Pin Descriptions
KS1 (Pin 1): The positive (+) Kelvin sense for the internal
current sense amplifier of Channel 1. Use a separate trace to
connect this pin to the current-sense point. It should be con-
nected to VIN as close as possible to the current-sense
resistor. When no current-sense resistor is used, connect as
close as possible to the drain node of the upper MOSFET.
ILIM1 (Pin 2): Current limit threshold setting for Channel 1. It
sinks a constant current of 9.9µA, which is converted to a
voltage across a resistor connected from this pin to VIN. The
voltage across the resistor is compared with either the V
the top MOSFET or the voltage across the external current
sense resistor to determine if an over-current condition has
occurred in Channel 1.
COMP1 (Pin 3): Compensation pin for Channel 1. This is the
output of the internal transconductance error amplifier. The
loop compensation network should be connected between
this pin and the signal ground, SGND (Pin 8).
FB1 (Pin 4): Feedback input for channel 1. Connect to VOUT
through a voltage divider to set the Channel 1 output voltage.
SYNC (Pin 5): The switching frequency of the LM5642 can
be synchronized to an external clock.
SYNC = LOW: Free running at 200kHz for LM5642, and at
375kHz for LM5642X. Channels are 180° out of phase.
SYNC = HIGH: Waiting for external clock
SYNC = Falling Edge: Channel 1 HDRV pin goes high.
Channel 2 HDRV pin goes high after 2.5µs delay. The maxi-
mum SYNC pulse width must be greater than 100ns.
For SYNC = Low operation, connect this pin to signal ground
through a 220kΩ resistor.
Order Number
LM5642MTCX
LM5642MHX
LM5642MTC
LM5642MH
28-Lead eTSSOP
Top View
28-Lead TSSOP
Package Type
20060102
NSC Package Drawing
DS
of
MXA28A
MTC28
2
UV_DELAY (Pin 6): A capacitor from this pin to ground sets
the delay time for UVP. The capacitor is charged from a 5µA
current source. When UV_DELAY charges to 2.3V (typical),
the system immediately latches off. Connecting this pin to
ground will disable the output under-voltage protection.
VLIN5 (Pin 7): The output of an internal 5V LDO regulator
derived from VIN. It supplies the internal bias for the chip and
powers the bootstrap circuitry for gate drive. Bypass this pin
to signal ground with a minimum of 4.7µF ceramic capacitor.
SGND (Pin 8): The ground connection for the signal-level cir-
cuitry. It should be connected to the ground rail of the system.
ON/SS1 (Pin 9): Channel 1 enable pin. This pin is internally
pulled up to one diode drop above VLIN5. Pulling this pin be-
low 1.2V (open-collector type) turns off Channel 1. If both ON/
SS1 and ON/SS2 pins are pulled below 1.2V, the whole chip
goes into shut down mode. Adding a capacitor to this pin pro-
vides a soft-start feature that minimizes inrush current and
output voltage overshoot.
ON/SS2 (Pin 10): Channel 2 enable pin. See the description
for Pin 9, ON/SS1. May be connected to ON/SS1 for simul-
taneous startup or for parallel operation.
FB2 (Pin 11): Feedback input for channel 2. Connect to
VOUT through a voltage divider to set the Channel 2 output
voltage.
COMP2 (Pin 12): Compensation pin for Channel 2. This is
the output of the internal transconductance error amplifier.
The loop compensation network should be connected be-
tween this pin and the signal ground SGND (Pin 8).
ILIM2 (Pin 13): Current limit threshold setting for Channel 2.
See ILIM1 (Pin 2).
KS2 (Pin 14): The positive (+) Kelvin sense for the internal
current sense amplifier of Channel 2. See KS1 (Pin 1).
2500 Units on Tape and Reel
2500 Units on Tape and Reel
Top View
48 units per Rail
48 units per Rail
Supplied As
20060194