ST1S10PHR View Datasheet(PDF) - STMicroelectronics

Part Name

Description

Manufacturer

ST1S10PHR

3 A, 900 kHz, monolithic synchronous step-down regulator

STMicroelectronics 

ST1S10

Application information

where TON is the ON time of the internal switch, given by:

TON = D/FS

The inductor should be selected with saturation current (ISAT) equal to or higher than the

inductor peak current, which can be calculated with the following equation:

IPK = IO + (ΔISW/2), ISAT ≥ IPK

The inductor peak current must be designed so that it does not exceed the switching current

limit.

5.7

Inductor (0.8 V < VOUT < 2.5 V)

For applications with lower output voltage levels (Vout < 2.5 V) the description in the previous

section is still valid but it is recommended to keep the inductor values in a range from 1µH to

2.2 µH in order to improve the DC-DC control loop behavior, and increase the output

capacitance depending on the VIN level as shown in the Figure 4 and Figure 5. In most

application conditions a 2.2 µH inductor is the best compromise between DC-DC control

loop behavior and output voltage ripple.

5.8

5.8.1

5.8.2

5.8.3

Function operation

Sync operation

The ST1S10 operates at a fixed frequency or can be synchronized to an external frequency

with the SYNC pin. The ST1S10 switches at a frequency of 900 kHz when the SYNC pin is

connected to ground, and can synchronize the switching frequency between 400 kHz to 1.2

MHz from an external clock applied to the SYNC pin. When the SYNC feature is not used,

this pin must be connected to ground with a path as short as possible to avoid any possible

noise injected in the SYNC internal circuitry.

Inhibit function

The inhibit pin can be used to turn OFF the regulator when pulled down, thus drastically

reducing the current consumption down to less than 6 µA. When the inhibit feature is not

used, this pin must be tied to VIN to keep the regulator output ON at all times. To ensure

proper operation, the signal source used to drive the inhibit pin must be able to swing above

and below the specified thresholds listed in the electrical characteristics section under VINH.

Any slew rate can be used to drive the inhibit pin.

OCP (over-current protection)

The ST1S10 DC-DC converter is equipped with a switch over-current protection. In order to

provide protection for the application and the internal power switches and bonding wires, the

device goes into a shutdown state if the switch current limit is reached and is kept in this

condition for the TOFF period (TOFF(OCP) = 135 µs typ.) and turns on again for the TON period

(TON(OCP) = 22 µs typ.) under typical application conditions. This operation is repeated cycle

by cycle. Normal operation is resumed when no over-current is detected.

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