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ST1S12GR
Synchronous rectification with inhibit, 0.7 A, 1.7 MHz adjustable, step-down switching regulator
February 2012 Doc ID 14314 Rev 5 1/20
ST1S12XX
ST1S12XX12, ST1S12XX18Synchronous rectification with enable, 0.7 A, 1.7 MHz fixed or
adjustable step-down switching regulator in TSOT23-5L
Features Step-down current mode PWM (1.7 MHz) DC-
DC converter 3% DC output voltage tolerance Synchronous rectification Fixed output voltage 1.2 V, 1.8 V, and ADJ
(available on request 1.5 V, 2.5 V and 3.3 V) Enable function Internal soft start Typical efficiency: > 90% 0.7 A output current capability Not switching quiescent current: max 650 µA
over temperature range RDSON typ. 250 mΩ and 400 mΩ Uses tiny capacitors and inductors Operative junction temp. -40 °C to 125 °C Available in TSOT23-5L package
DescriptionThe ST1S12 is a step down DC-DC converter
optimized for powering low-voltage digital cores in
HDD applications and, generally, to replace the
high current linear solution when the power
dissipation may cause high heating of the
application environment. It provides up to 0.7 A
over an input voltage range of 2.5 V to 5.5 V. A
high switching frequency (1.7 MHz) allows the
use of tiny surface-mount components. In addition
to the resistor divider to set the output voltage
value, only an inductor and two capacitors are
required. Moreover, a low output ripple is
guaranteed by the current mode PWM topology
and by the use of low ESR SMD ceramic
capacitors. The device is thermally protected and
the current is limited to prevent damage due to
accidental short-circuit. The ST1S12 is available
in the TSOT23-5L package.
Table 1. Device summary
Contents ST1S12XX, ST1S12XX12, ST1S12XX182/20 Doc ID 14314 Rev 5
Contents Schematic . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 Pin configuration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Maximum ratings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Electrical characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Typical application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 Application notes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 Typical performance characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19
ST1S12XX, ST1S12XX12, ST1S12XX18 SchematicDoc ID 14314 Rev 5 3/20
1 Schematic
Figure 1. Schematic diagram
Pin configuration ST1S12XX, ST1S12XX12, ST1S12XX184/20 Doc ID 14314 Rev 5
Pin configuration
Figure 2. Pin connections (top view)
Table 2. Pin description
ST1S12XX, ST1S12XX12, ST1S12XX18 Maximum ratingsDoc ID 14314 Rev 5 5/20
3 Maximum ratings Note: Absolute maximum ratings are the values beyond which damage to the device may occur.
Functional operation under these conditions is not implied.
Table 3. Absolute maximum ratings
Table 4. Thermal data
Table 5. ESD performance
Electrical characteristics ST1S12XX, ST1S12XX12, ST1S12XX186/20 Doc ID 14314 Rev 5
4 Electrical characteristicsVIN = VEN = 3.6 V, CIN = 4.7 µF , CO = 10 µF, L = 2.2 µH, TJ = - 40 to 125 °C (unless
otherwise specified. Typical values are referred to 25 °C).
Table 6. Electrical characteristics for ST1S12G Guaranteed by design, but not tested in production.
ST1S12XX, ST1S12XX12, ST1S12XX18 Electrical characteristicsDoc ID 14314 Rev 5 7/20
VIN =VEN = 3 V, CIN = 4.7 µF, CO =10 µF, L = 2.2 µH, TJ = -40 to 125 °C (unless otherwise
specified. Typical values are referred to 25 °C).
Table 7. Electrical characteristics for ST1S12G12 Guaranteed by design, but not tested in production.
Electrical characteristics ST1S12XX, ST1S12XX12, ST1S12XX188/20 Doc ID 14314 Rev 5
VIN =VEN = 3.6 V, CIN = 4.7 µF, CO =10 µF , L = 2.2 µH, TJ = -40 to 125 °C (unless otherwise
specified. Typical values are referred to 25 °C).
Table 8. Electrical characteristics for ST1S12G18 Guaranteed by design, but not tested in production.
ST1S12XX, ST1S12XX12, ST1S12XX18 Typical applicationDoc ID 14314 Rev 5 9/20
5 Typical application
Figure 3. Application circuit
Application notes ST1S12XX, ST1S12XX12, ST1S12XX1810/20 Doc ID 14314 Rev 5
6 Application notesThe ST1S12 is an adjustable current mode PWM step-down DC-DC converter with internal
0.7 A power switch, packaged in TSOT23-5L. This device is a complete 0.7 A switching
regulator, with its internal compensation eliminating the need for additional components.
Because the ST1S12 an adjustable regulator, the output voltage is determined by an
external resistor divider. The desired value is derived by the following equation:
Equation 1VO = VFB [1 + R1 / R2]
For the device to function only a few component are required: an inductor, two capacitors
and the resistor divider. The inductor selected must be capable of non saturation at peak
current level. Moreover, its value can be selected taking into account that a large inductor
value increases efficiency at low output current and reduces output voltage ripple, while a
smaller inductor can be used when it is important to reduce package size and the total cost
of the application. Finally, the ST1S12 has been designed to work properly with X5R or X7R
SMD ceramic capacitors both at the input and at the output. These types of capacitors, due
to their very low series resistance (ESR), minimize the output voltage ripple. Other low ESR
capacitors can be used according to the need of the application without compromising the
correct functioning of the device.
