5

Functional Pin Descriptions

VCC (Pin 28)

Provide a 12V bias supply for the IC to this pin. This pin also

provides the gate bias charge for all the MOSFETs

controlled by the IC. The voltage at this pin is monitored for

Power-On Reset (POR) purposes.

GND (Pin 17)

Signal ground for the IC. All voltage levels are measured

with respect to this pin.

PGND (Pin 24)

This is the power ground connection. Tie the synchronous

PWM converter’s lower MOSFET source to this pin.

VAUX (Pin 16)

Connect this pin to the ATX 3.3V output. The voltage present

at this pin is monitored for sequencing purposes. This pin

provides the necessary base bias for the NPN pass

transistors, as well as the current sunk through the 5k

Ω VID

pull-up resistors.

SS13 (Pin 13)

Connect a capacitor from this pin to ground. This capacitor,

along with an internal 28

µA current source, sets the soft-start

delayed by the time interval required by the charging of this

capacitor from 0V to 1.25V (see Soft-Start details).

SS24 (Pin 12)

Connect a capacitor from this pin to ground. This capacitor,

along with an internal 28

µA current source, sets the soft-start

interval of the standard buck converter. Pulling this pin below

0.8V induces a chip reset (POR) and shutdown.

VTTPG (Pin 9)

VTTPG is an open collector output used to indicate the

status of the standard buck regulator output voltage. This pin

is pulled low when the output is below the under-voltage

threshold or when the SS13 pin is below 1.25V.

LGATE Source

-

1

-

A

LGATE Sink

-

1.4

3.0

Ω

PROTECTION

VSEN1 Over-Voltage (VSEN1/DACOUT)

VSEN1 Rising

-

120

-

%

OCSET1,2 Current Source

170

200

230

µA

Soft-Start Current

-28-

µA

POWER GOOD

VSEN1 Upper Threshold

(VSEN1/DACOUT)

VSEN1 Rising

108

-

110

%

VSEN1 Under-Voltage

(VSEN1/DACOUT)

VSEN1 Rising

92

-

94

%

VSEN1 Hysteresis (VSEN1/DACOUT)

VSEN1 Falling

-

2

-

%

PGOOD Voltage Low

-

-

0.8

V

VSEN2 Under-Voltage

VSEN2 Rising

-

1.00

-

V

VSEN2 Hysteresis

VSEN2 Falling

-

60

-

mV

VTTPG Voltage Low

-

-

0.8

V

NOTE:

2. Guaranteed by design

Electrical Specifications

Recommended Operating Conditions, Unless Otherwise Noted. Refer to Figures 1, 2 and 3 (Continued)

PARAMETER

SYMBOL

TEST CONDITIONS

MIN

TYP

MAX

UNITS

Typical Performance Curve

FIGURE 4. BIAS SUPPLY CURRENT vs FREQUENCY

100

200

300

400

500

600

700

800

900

1000

SWITCHING FREQUENCY (kHz)

140

120

100

80

60

40

20

0

C = 660pF

C = 1500pF

C = 3600pF

C = 4800pF

ISL6523A