ISL78233, ISL78234

2

FN8359.5

April 23, 2015

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ISL78233, ISL78234

(16 LD TQFN)

TOP VIEW

1

3

4

VIN

VDD

SYNC

2

7

5

6

FB

PGND

PG

8

11

9

10

16

13

15

14

12

SGND

PGND

Pin Descriptions

PIN NUMBER

SYMBOL

DESCRIPTION

1, 16

VIN

Input supply voltage. Place a minimum of two 22µF ceramic capacitors from VIN to PGND as close as

possible to the IC for decoupling.

2

VDD

Input supply voltage for the logic. Connect to VIN pin.

3

PG

Power-good is an open-drain output. Use a 10kΩ to 100kΩ pull-up resistor connected between VIN and

PG. At power-up or EN HI, PG rising edge is delayed by 1ms upon output reached within regulation.

4

SYNC

Mode Selection pin. Connect to logic high or input voltage VIN for PWM mode. Connect to logic low or

ground for PFM mode. Connect to an external function generator for synchronization with the positive

edge trigger. There is an internal 1MΩ pull-down resistor to prevent an undefined logic state in case

of SYNC pin float.

5

EN

Regulator enable pin. Enable the output when driven to high. Shutdown the chip and discharge output

capacitor when driven to low.

6

FS

This pin sets the oscillator switching frequency, using a resistor, RFS, from the FS pin to GND. The

frequency of operation may be programmed between 500kHz to 4MHz. The default frequency is 2MHz

if FS is connected to VIN.

7

SS

SS is used to adjust the soft-start time. Set to SGND for internal 1ms rise time. Connect a capacitor from

SS to SGND to adjust the soft-start time. Do not use more than 33nF per IC.

8, 9

COMP, FB

The feedback network of the regulator, FB, is the negative input to the transconductance error

amplifier. COMP is the output of the amplifier if COMP not tied to VDD. Otherwise, COMP is

disconnected thru a MOSFET for internal compensation. Must connect COMP to VDD in internal

compensation mode. The output voltage is set by an external resistor divider connected to FB. With a

properly selected divider, the output voltage can be set to any voltage between the power rail (reduced

by converter losses) and the 0.6V reference. There is an internal compensation to meet a typical

application. Additional external networks across COMP and SGND might be required to improve the

loop compensation of the amplifier operation.

In addition, the regulator power-good and undervoltage protection circuitry use FB to monitor the

regulator output voltage.

10

SGND

Signal ground

11, 12

PGND

Power ground

13, 14, 15

PHASE

Switching node connections. Connect to one terminal of the inductor. This pin is discharged by a 100Ω

resistor when the device is disabled. See “Functional Block Diagram” on page 4 for more detail.

Exposed Pad

-

The exposed pad must be connected to the SGND pin for proper electrical performance. Place as

many vias as possible under the pad connecting to SGND plane for optimal thermal performance.