SC186 datasheet(14/18 Pages) SEMTECH

14 / 18 page

SC186

Applications Information (continued)

load resistance. When the load presented falls below the

current limit holding level, the output will charge to the

upper PSAVE voltage threshold and return to normal

operation. The SC186 is capable of sustaining an indefi-

nite short circuit without damage. During the soft start, if

current limit has occurred before the SS voltage has

reached 400mV, the part enters foldback current limit

mode. Foldback current limit mode will be disabled during

soft-start after the SS voltage is higher than 400mV.

Over-Voltage Protection

In the event of a 15% over-voltage on the output, the

PWM drive is disabled with the LX pin floating. Switching

does not resume until the output voltage falls below the

nominal V

OUT regulation voltage.

Programmable Output Voltage

The SC186 has fifteen pre-determined output voltage

values which can be individually selected by program-

ming the CTL input pins (see Table 1 — Output Voltage

Settings). Each CTL pin has an active 500kΩ internal pull-

down resistor. The 500kΩ resistor is switched in circuit

whenever the CTL input voltage is below the input thresh-

old, or when the part is in under voltage lockout. It is

recommended to tie all high CTL pins together and use an

external pull-up resistor to AVIN if there is no enable signal

or if the enable input is an open drain/collector signal. The

CTL pins may be driven by a microprocessor to allow

dynamic voltage adjustment for systems that reduce the

supply voltage when entering sleep states. Avoid all zeros

being present on the CTL pins when changing program-

mable output voltages as this would disable the device.

SC186 is also capable of regulating a different (higher)

output voltage, which is not shown in the Table 1, via an

external resistor divider. There will be a typical 2μA current

flowing into the VOUT pin. The typical schematic for an

adjustable output voltage option from the standard 1.0V

with CTLx=[0010], is shown in Figure 2. RFB1 and RFB2 are

used to adjust the desired output voltage. If the RFB2

current is such that the 2μA VOUT pin current can be

ignored, then RFB1 can be found using the next equation.

RFB2 needs to be low enough in value for the current

through the resistor chain to be at least 20μA in order to

ignore the VOUT pin current.

CTL0

CTL1

PGND

AVIN

VOUT

SC186

PVIN

CTL2

AGND

CTL3

PGOOD

SSA

CSS

10nF

VOUT

COUT

RFB2

10kΩ

CFF

RFB1

RFB1 = (VOUT-1)

x RFB2

for CTLX = 0010

(1.0V)

VIN

CAVIN

0.1µF

RAVIN-1Ω

CIN

22µF

RPGOOD

100kΩ

Enable

Figure 2 — Output Voltage Programming

OSTD

OUT

where V

OSTD is the pre-determined output voltage via the

CTL pins.

FF is needed to maintain good transient response perfor-

mance. The correct value of C

FF can be found using the

following equation.

)

(

]

[

]

[

OSTD

OUT

To simplify the design, it is recommended to program the

desired output voltage from a standard 1.0V as shown in

Figure 2 with a proper C

FF calculated from Equation 2. For

programming the output voltage from other standard

voltages, R

FB1, RFB2 and CFF need to be adjusted to conform

to the previous equations.

Shut Down

When all CTL pins are low, the device will run in shutdown

mode, drawing less than 1μA from the input power supply.

The internal switches and band-gap voltage will be imme-

diately turned off.

Thermal Shutdown

The device has a thermal shutdown feature to protect the

SC186 if the junction temperature exceeds 160°C. During

thermal shutdown, the on-chip power devices are dis-

abled, floating the LX output. When the temperature

drops by 10°C, it will initiate a soft start cycle to resume

normal operation.

SC186 Datasheet(PDF) 14 Page - Semtech Corporation

SC186 Datasheet(HTML) 14 Page - Semtech Corporation

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Datasheet Download

Link URL