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4

Aout

Output of the error amplifier for the main converter. This pin typically drives an optocoupler and is

also used for compensation along with Ainv (pin #5).

5

Ainv

Main loop error amplifier inverting input. The non-inverting input is connected to an internal 2.5V

reference that can be digitally trimmed. A high impedance internal divider from +12V and +5V

UV/OV sense pins (#23, #24) eliminates the need for external divider in most applications. The

pin is used for error amplifier compensation.

6

12Visns

Input pin for 12V current sense. Together with the 12V OV/UV sense pin (#24), this pin measures

the voltage across a current sense resistor in series with the output. If the load current exceeds a

preset threshold, MFAULT (#1) will go high. Depending on the mode set, MFAULT will be latched

off or pulled low again after about 1 second to allow autorecovery. To disable this function the pin

may be left open, shorted to ground or shorted to the 12V UV/OV pin.

7

5Visns/

3V3isns

Input pin for 5V or 3V3 current sense. Together with the OV/UV sense pin (#23 or #22), this pin

measures the voltage across a current sense resistor in series with the output. If the load current

exceeds a preset threshold, MFAULT (#1) will go high. Depending on the mode set, MFAULT will

be latched off or pulled low again after about 1 second to allow autorecovery. To disable this

function the pin may be left open, shorted to ground or shorted to the 5V UV/OV pin.

8

Cout

Auxiliary loop optocoupler drive. Also node for error amp compensation. Large signal slew rate is

limited to reduce sensitivity to switching noise.

9

Cinv

Inverting input for Auxiliary error amplifier. The non-inverting input is connected to an internal

1.25V reference that can be digitally trimmed.

10

Dmon

Dual or Auxiliary UV/OV monitor, Dmon is programmable to monitor 3V3 or 5V. To allow a correct

power up, the UV function on this pin is blanked out during initial start-up. There is no delay for

the OV function.

11

DFAULT

Dual or Auxiliary fault protection. When Dmon (#10) recognizes an over voltage, DFAULT and

MFAULT (#1) go high. DFAULT is capable of sourcing up to 50mA. Possible applications are a

crowbar across the Auxiliary output or an opto-coupled fault signal to the primary side.

12

Vdd

Positive input supply voltage. Vdd is normally supplied from the Auxiliary power supply output

voltage. If Vdd-UVL detects a sustained under voltage, PW-OK (#14) will be pulled low and

sending MFAULT (#1) high will disable the main converter.

13

ACsns

Analog of bulk voltage for AC fail warning. The usual source of this analog pin is one of the

secondary windings of the main transformer. Hysteresis is provided through a trimmable 50

µA

current sink on this pin that is activated as the voltage at the pin falls below the internal reference

(2.5V).

14

PW-OK

/Data

Power good signal for the Main converter. When asserted high, this pin indicates that the

voltages monitored are above their UV limits. There will be typically 250ms delay from the Main

outputs becoming good and PW-OK being asserted. This is nominally an open drain signal. To

improve robustness, this output has a limited current sink capability. In programming mode, this

pin is used for data input; then the absolute maximum rating will be Vdd+0.5V.

15

PS-ON /

Clock

Control pin to enable the Main converter. This pin has debouncing logic. A recognized high value

on this pin will cause PW-OK (#14) to go immediately low and, after a delay of 2.5ms, to shut

down the main PWM by allowing MFAULT (#1) to go high. During normal operation (or if not

used) this pin has to be connected to a voltage lower than 0.8V. In programming mode, this pin

will be used to clock serial data into the chip.

16

VREF

2.5V reference for external applications. This is a buffered pin. Shorting this pin to ground or to

Vdd (#12) will not affect integrity of control or monitor references. An external capacitor (max.

100nF) is required whenever the pin is loaded (up to 5 mA), otherwise it can be left floating.

PIN DESCRIPTION (continued)

Pin #

Name

Description