FUNCTIONAL PIN DESCRIPTION

ENABLE(pin1): Enable input. A

high level

(>2.4V) enables the device, a low level (<0.8V)

shuts it down. As ENABLE drops below 0.8V, the

drivers are turned off and all internal functions are

disabled except REG5. In this condition the stand

by current is less than 80

µA at VIN = 12V.

VIN(pin2): Device supply voltage. Input voltage

range at this pin is 4.75V to 25V and the operat-

ing current requirement at 12V is 650

µA.

REG5(pin3): 5V Regulator supply. Used also to

supply the bootstrap capacitor. A minimum 2.2

µF

ceramic capacitor connected to PWRGND is re-

quired.

V5SW(pin4): 5V supply line. Connecting to 5V

bus(4.75V to 5.5V) the device is no longer pow-

ered by VIN but by this pin and the internal linear

regulator is disconnected increasing the effi-

ciency.

DISPROT (pin5) Disable Protection Functions. A

high level (3.3V CMOS LOGIC) on this pin dis-

ables the undervoltage and the overvoltage pro-

SSTART(pin6): Soft Start. The soft-start time is

programmed by an external capacitor connected

between this pin and SGND. The internal current

generator forces 4

µA through the capacitor imple-

menting the soft start function.

HRSNS(pin7): Error summing current sense non

inverting input.

LRSNS(pin8): Error summing current sense in-

verting input.

VFB(pin9): Regulator voltage feedback input.

Connect close to the CPU input supply pin realise

an accurate voltage regulation. VFB internally is

connected to the window comparator that is used

to increase the performance during the load tran-

sient.

COMP(pin10): Regulator stability compensation

pin. The compensation is realised internally and

normally it is not necessary to connect any exter-

nal components to this pin.

VPROG(pin11): Reference voltage test pin. This

pin provides the DAC output and should be de-

coupled to ground using a 0.22

µF ceramic ca-

pacitor. No load has to be connected.

SNSGND(pin12): Remote ground sense. This

pin is internally connected to the low power cir-

cuitry and for a precise output voltage regulation

can be connected to the output capacitor nega-

tive terminal.

able on-chip a linear regulator useful for the 2.5V

bus. A max input voltage of 3.3V is recom-

mended at Iomax (150mA).

linear regulator is realised with an internal NPN

transistor

with +/-2% output accuracy. A mini-

mum

of

47

µF capacitor connected versus

PWRGND is required.

VBG(pin15): Band-gap reference voltage. A min

220nF ceramic capacitor is required to assure the

band gap stability and noise immunity.

VSS(pin16): Signal ground. This pin could be

connected to the PWRGND pin.

FREQ(pin17): Connecting an external resistor

versus ground is possible to select the switching

frequency between 100kHz and 1MHz. Using an

Rext=680k the fsw is 100kHz, using an Rext =

40k the fsw is 1MHz. In this condition is recom-

mended to connect the OSC pin to REG5 or to

VSS.

OSC(pin18): Connecting to REG5 is able to set

the switching frequency at 200kHz, connecting to

VSS is able to set the switching frequency at

250kHz. An external pulsed signal, with an ampli-

tude higher than 2.4V, could synchronise the de-

vice. In all these conditions pin FREQ has to be

connected to REG5.

OVP/CURLIM(pin19): Over voltage protection

and reduced current limit window. If the output

voltage reaches the 10% above the programmed

voltage (VPROG) this pin is driven low the high

side driver is turned off and the low, side driver is

turned on. All the internal blocks are active. The

device uses OVP function to discharge the output

during HIGH_TO_LOW core voltage transition.

The pin is driven low also during LOW_TO_HIGH

core voltage transition. The pin will stay low as

L5996

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