ML4818 查看數據表（PDF） - Fairchild Semiconductor

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ML4818

Phase Modulation/Soft Switching Controller

Fairchild Semiconductor 

ML4818

7

6

5

4

3

SOURCE

2

SINK

1

0

0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

OUTPUT CURRENT (A)

Figure 8. Output Drive Saturation Voltage vs.

Output Current

15

10

5 1nF

10nF

1nF

10nF

PRODUCT SPECIFICATION

Output Driver Stage

The ML4818 has four high current high speed totem pole

output drivers each capable of 1.5A peak output, designed to

quickly switch the gates of capacitive loads, such as power

MOSFET transistors. Figure 8 illustrates the saturation char-

acteristics of the ouput drive transistors shown in Figure 7.

Typical rise and fall time characteristics of the output drivers

are illustrated with capacitive loads of 1nF and 10nF in

Figure 9.

Current Limit, Fault Detection and Soft Start

Current limit is implemented when the current sensed on ILIM

reaches the 1V limit. At this point, the PWM cycle is termi-

nated. The flip flop (Figure 10) turns on the current source to

charge CRST and remains on for the duration of the clock

period. When CRST has charged to 3.4V, a soft start reset

occurs. The number of times the PWM cycle is terminated

due to over-current is “remembered” on CRST. Over time,

CRST is discharged by RRST providing a measure of “forget-

ting” when the over-current condition no longer occurs. This

integrating fault detection is useful in differentiation between

short circuit and load surge conditions.

100 200

tF

(ns)

100 200

tR

Figure 9. Output Rise/Fall Time

ISWITCH

CSS

SOFT START

9

R1

RSENSE

ILIM

4

C1

+

1V

–

V+

V+

I1

TERMINATE

PWM CYCLE

S

Q

RRST

I2

CRST

12

RCRESET

R

CLOCK

+

3.4V

1.3V

–

INHIBIT

OUTPUT

UNDER-VOLTAGE

LOCKOUT

Figure 10. Over-Current, Soft-Start, and Integrating Fault Detect Circuits

8

REV. 1.0.3 6/21/01

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