Linear Technology DC852A - LTC4354 Negative Voltage Diode-OR Controller and Monitor DC852A DC852A Data Sheet

LTC4354

9

4354fc

The worst-case power dissipation in R

IN

:

 

 

P

=

(72V

−10.5V)

2

12k

= 0.315W

Choose a 12k 0.5W resistor or use two 5.6k 0.25W resis-

tors in series.
Next, choose the N-channel MOSFET. The 100V, IRF3710S 

in DD-Pak package with R

DS(ON)

 = 23mΩ (max) offers a 

good solution. The maximum voltage drop across it is: 
 ∆V = (5A)(23mΩ) = 115mV
The maximum power dissipation in the MOSFET is a mere:
  P = (5A)(115mV) = 0.6W
R1 and R2 are chosen to be 2k to protect DA and DB pins 

from being damaged by high voltage spikes that can occur 

during an input supply fault.

The LED, D1, requires at least 1mA of current to fully turn 

on, therefore R3 is set to 33k to accommodate lowest 

input  supply voltage of –36V.

Layout Considerations
The following advice should be considered when laying 

out a printed circuit board for the LTC4354.
The bypass capacitor provides AC current to the device 

so place it  as close to the V

CC

 and V

SS

 pins as possible. 

The inputs to the servo amplifiers, DA, DB and V

SS

 pins, 

should be connected directly to the MOSFETs’ terminals 

using Kelvin connections for good accuracy.
Keep the traces to the MOSFETs wide and short. The PCB 

traces associated with the power path through the MOSFETs 

should have low resistance.

LTC4354

LOAD

DB

GA

DA

GB

V

SS

V

B

 = –5.2V

V

A

 = –5.2V

GND

FAULT

M2

Si4466DY

M1

Si4466DY

4354 TA02

V

CC

R3

2k

D1

LED

C

IN

1µF

2, 5

6

1

4

8

3

7

12V

470Ω

240Ω*

1.2V, 200A

OUTPUT BUS

4354 TA03

*OPTIONAL PRELOAD 

HAT2165 ×6

HAT2165 ×6

1.2V

100A

INPUT

1µF

V

EE

GA,GB

V

CC

LTC4354

DA,DB

12V

470Ω

240Ω*

1.2V

100A

INPUT

1µF

V

EE

GA,GB

V

CC

LTC4354

DA,DB