8

FN6418.4

March 18, 2008

23

LGATE2

SMPS2 Synchronous-Rectifier Gate-Drive Output. LGATE2 swings between GND and PVCC.

24

BOOT2

Boost Flying Capacitor Connection for SMPS2. Connect to an external capacitor according to the “Typical Application

Circuits” starting on page 21 (Figures 62, 63 and 64) See “MOSFET Gate Drivers (UGATE_, LGATE_)” on page 28.

25

PHASE2

Inductor Connection for SMPS2. PHASE2 is the internal lower supply rail for the UGATE2 high-side gate driver.

PHASE2 is the current-sense input for the SMPS2.

26

UGATE2

High-Side MOSFET Floating Gate-Driver Output for SMPS2. UGATE1 swings between PHASE2 and BOOT2.

27

EN2

SMPS2 Enable Input. The SMPS2 is enabled if EN2 is greater than the logic high level and disabled if EN2 is less than

the logic low level. If EN2 is connected to REF, the SMPS2 starts after the SMPS1 reaches regulation (delay start).

Drive EN2 below 0.8V to clear fault level and reset the fault latches.

28

POK2

SMP2 Power-Good Open-Drain Output. POK2 is low when the SMPS2 output voltage is more than 10% below the

normal regulation point or during soft-start. POK2 is high impedance when the output is in regulation and the soft-start

circuit has terminated. POK2 is low in shutdown.

29

SKIP

Low-Noise Mode Control. Connect SKIP to GND for normal Idle-Mode (pulse-skipping) operation or to VCC for PWM

mode (fixed frequency). Connect to REF or leave floating for ultrasonic skip mode operation.

30

OUT2

SMPS2 Output Voltage-Sense Input. Connect to the SMPS2 output. OUT2 is an input to the Constant on-time-PWM

on-time one-shot circuit. It also serves as the SMPS2 feedback input in fixed-voltage mode.

31

ILIM2

SMPS2 Current-Limit Adjustment. The GND-PHASE1 current-limit threshold is 1/10th the voltage seen at ILIM2 over

a 0.2V to 2V range. There is an internal 5µA current source from VCC to ILIM2. Connect ILIM2 to REF for a fixed

200mV. The logic current limit threshold is default to 100mV value if ILIM2 is higher than VCC - 1V.

32

REFIN2

Output voltage control for SMPS2. Connect REFIN2 to VCC for fixed 3.3V. Connect REFIN2 to a 3.3V supply for fixed

1.05V. REFIN2 can be used to program SMPS2 output voltage from 0.5V to 2.50V. SMPS2 output voltage is 0V if

REFIN2 < 0.5V.

PIN

NAME

FUNCTION

Typical Performance Curves

0

10

20

30

40

50

60

70

80

90

100

0.001

0.010

0.100

OUTPUT LOAD (A)

1.000

10.000

0

10

20

30

40

50

60

70

80

90

100

0.010

0.100

1.000

10.000

OUTPUT LOAD (A)

0.001

ISL6237