APPLICATION NOTES

VIN A,B - These pins provide the input power connection to the

MSK5805RH. This is the supply that will be regulated to the output.

Both pins must be connected for proper operation.

VBIAS - This pin provides power to all internal circuitry including bias,

start-up, thermal limit and overcurrent latch. VBIAS voltage range is 2.9V

to 7.5V. VBIAS should be kept greater than or equal to VIN.

GND1 - Internally connected to signal ground, these pins should be

connected externally by the user to the circuit ground and the GND2 pins.

LATCH - The MSK5805RH LATCH pin is used for both current limit and

thermal limit. A capacitor between the LATCH pin and ground sets a

time out delay in the event of an over current or short circuit condition.

The capacitor is charged to approximately 1.6V from a 7.2µA (nominal)

current source. Exceeding the thermal limit will charge the latch capac-

itor from a larger current source for a near instant shutdown. Once the

latch capacitor is charged the device latches off until the latch is reset.

Momentarily pull the LATCH pin low, toggle the shutdown pin high then

low or cycle the power to reset the latch. Toggling the shutdown pin or

cycling the bias power both disable the device during the reset operation

(see SHUTDOWN pin description). Pulling the LATCH pin low immedi-

ately enables the device for as long as the LATCH pin is held low plus

the time delay to re-charge the latch capacitor whether or not the fault

has been corrected. Disable the latch feature by tying the LATCH pin

low. With the LATCH pin held low the thermal limit feature is disabled

and the current limit feature will force the output voltage to droop but

remain active if excessive current is drawn.

SHUTDOWN - There are two functions to the SHUTDOWN pin. It may be

used to disable the output voltage or to reset the LATCH pin. To activate

the shutdown/reset functions the user must apply a voltage greater than

1.3V to the SHUTDOWN pin. The voltage applied to the SHUTDOWN

pin can be greater than the input voltage. The output voltage will turn

on when the SHUTDOWN pin is pulled below the threshold voltage.

If the SHUTDOWN pin is not used, it should be connected to ground.

FB - The FB pin is the inverting input of the internal error amplifier. The

non-inverting input is connected to an internal 1.265V reference. This

error amplifier controls the drive to the output transistor to force the FB

pin to 1.265V. An external resistor divider is connected to the output, FB pin

and ground to set the output voltage.

GND2 - Internally connected to power ground, these pins should be

connected externally by the user to the circuit ground and the GND1 pins.

VOUT A,B - These are the output pins for the device. Both pins must

be connected for proper operation.

IADJ1 AND IADJ2 - The IADJ pins provide a method to adjust the cur-

rent limit. The current limit of the MSK5805RH is sensitive to the input

voltage. For lower input voltages the current limit is reduced. For higher

input voltages current limit is increased. Place a short across IADJ1 and

IADJ2 for maximum current. Place a resisitor across IADJ1 and IADJ2

to decrease the current limit.

As previously mentioned, the LATCH pin provides over current/output

short circuit protection with a timed latch-off circuit. Reference the LATCH

pin description note. The latch off time out is determined with an external

capacitor connected from the LATCH pin to ground. The time-out period

is equal to the time it takes to charge this external capacitor from 0V

to 1.6V. The latch charging current is provided by an internal current

source. This current is a function of bias voltage and temperature (see

latch charging current curve). For instance, at 25°C, the latch charging

current is 7.2µA at VBIAS=3V and 8µA at VBIAS=7V.

In the latch-off mode, some additional current will be drawn from the

bias supply. This additional latching current is also a function of bias

voltage and temperature (see typical performance curves).

The MSK5805RH current limit function is directly affected by the input

and output voltages. Custom current limit is available; contact the factory

for more information.

3

START UP OPTIONS

The MSK5805RH starts up and begins regulating immediately when

VBIAS and VIN are applied simultaneously. Applying VBIAS before VIN

starts the MSK5805RH up in a disabled or latched state. When starting

in a latched state the device output can be enabled either by pulling the

latch pin low to drain the latch capacitor or pulsing the shutdown pin high.

The shutdown pulse duration is partially dependent upon the size of the

latch capacitor and should be characterized for each application; 30uS

is typically adequate for a 1uF latch capacitor at 25°C. A momentary high

pulse on the shutdown pin can be achieved using the RC circuit below

if VIN rises rapidly. The resistor and capacitor must be selected based

on the required pulse duration, the rise characteristic of VIN and the

shutdown pin threshold (see shutdown pin threshold and current curves).

The shutdown pin can be held high and pulled low after VIN comes up

or the latch pin held low and released after VIN comes up to ensure

automatic startup when applying VBIAS before VIN. Either of the basic

circuits below can be adapted to a variety of applications for automatic

start up when VBIAS rises before VIN.

PIN FUNCTIONS

OVERCURRENT LATCH-OFF/LATCH PIN CAPACITOR

SELECTION

OUTPUT CAPACITOR SELECTION

Low ESR capacitance at the output is required to maintain regulation

and stability. A single 150µA (AVX PN TAZX157K010L) in parallel with

ceramic decoupling capacitance (0.01µF typical) ensure good stability

margins and transient performance for the broadest range of applica-

tions. Lower value output capacitors can also provide acceptable per-

formance in applications with defined operating ranges. For example,

a single 47µF (AVX PN TAZH476K010L) performs well in lower current

applications. Additional frequency response compensation can be im-

plemented with a simple RC network from pin 6 to the output or ground.

Reference the MSK5805RH Evaluation Card Application Note (AN033)

for more information.

POWER SUPPLY BYPASSING

To maximize transient response and minimize power supply transients

it is recommended that a 33µF minimum tantalum capacitor is connected

between VIN and ground. A 0.1µF ceramic capacitor should also be used

for high frequency bypassing.

8548-111 Rev. F 5/15