LM3753 Datasheet, PDF (3/38 Pages) National Semiconductor (TI) – Scalable 2-Phase Synchronous Buck Controllers with Integrated FET Drivers and Linear Regulator Controller

Pin Descriptions
Pin Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
Pin Name
HG2
SW2
LG2
VDD
PGND
LG1
SW1
HG1
BOOT1
PGOOD
SYNCOUT
SYNC
FAULT
NBASE
VIN
VCC
SGND
COMP
FB
VDIF
SNSM
SNSP
Description
Gate drive of the high-side N-channel MOSFET for Phase 2.
Switching node of the power stage of Phase 2.
Gate drive of the low-side N-channel MOSFETs for Phase 2.
Power supply for gate drivers. Decouple VDD to PGND with a ceramic capacitor. VDD can either
be supplied by an external 5V ±10% bus, or by the internal regulator, which uses an external
NPN pass device. If using the internal regulator, connect VDD to the emitter of the NPN pass
device.
Power Ground. Tie PGND and SGND together on the board through the DAP.
Gate drive of the low-side N-channel MOSFETs for Phase 1.
Switching node of the power stage of Phase 1.
Gate drive of the high-side N-channel MOSFET for Phase 1.
Bootstrap of Phase 1 for the high-side gate drive power supply.
Power Good open-drain output. Active HIGH.
Synchronization Output. For multi-controller systems this pin should be connected to the SYNC
pin of the next controller in daisy-chain configuration
Synchronization Input. SYNCOUT of one controller is connected to SYNC of the next controller
in a daisy-chain fashion. To synchronize the whole chain of controllers to an external clock, wire
the external clock to the SYNC pin of the first controller of the chain (called the Master controller).
Otherwise, connect the SYNC input of the Master controller to ground and all of the controllers
will be controlled by the internal oscillator of the Master.
Input/Output. Wire the FAULT pin of all controllers together. FAULT gets pulled Low during
startup, an over-current fault, or an over-voltage fault. FAULT = Low signals all controllers to stop
switching and prepare for the next startup sequence. The first LM3753/54 in the system (the
Master) supplies the FAULT pin pull-up current for all of the controllers.
Connect to the base of external series-pass NPN if using the LM3753/54 internal LDO controller
to generate VDD. Otherwise leave unconnected.
Input Voltage. Connect VIN to the input supply rail used to supply the power stages. This input
is used to provide the feed-forward for the voltage control of V_OUT and for generating the internal
VCC voltage.
Supply for internal control circuitry. Decouple VCC to PGND with a ceramic capacitor. When VIN
> 5.5V, the internal LDO will supply 4.35V to this pin. When 4.5V < VIN < 5.5V, connect VIN to
VCC. In this case the internal VCC LDO will turn off and VCC current will be supplied directly by
VIN.
Signal Ground. Tie PGND and SGND together on the board through the DAP.
Error Amplifier Output. For the Master, a compensation network is placed between the COMP
pin and the FB pin. The COMP pin of the Master should be connected to the SNSP pin of each
of the Slaves. The COMP pin of each of the Slaves must be connected to its VDIF pin
Feedback Input. This is the inverting input of the error amplifier. Connect the Master FB pin to
the output voltage divider and compensation network. Connect each Slave FB pin to its own VCC
pin. This will put that controller in Slave mode and disable its error amplifier.
Output of the remote-sense differential amplifier. Connect the Master VDIF pin to the output
voltage divider and compensation network. The Slave differential amplifier is used to buffer
COMP from the Master controller. Connect each Slave VDIF pin to its own COMP pin.
Inverting input of the remote-sense differential amplifier. Connect SNSM of the Master controller
to PGND at the load point. On Slave controllers, the differential amplifier is used to buffer COMP
from the Master controller. Connect SNSM of each Slave controller directly to the Master
controller SGND pin.
Non-inverting input of the remote-sense differential amplifier. Connect the SNSP of the Master
controller to V_OUT at the load point. On Slave controllers, the differential amplifier is used to buffer
COMP of the Master controller. Connect SNSP of each Slave controller to the Master controller
COMP pin.
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