PDF《TMS320F28xx and TMS320F28xxx DSP》

5 V are shown in Table 2. Switching power supplies inherently have more noise and ripple than linear regulators;

so, if low noise and ripple is required, consider using a linear regulator like the TPS767D301. For more information on the TPS767D301, see the TPS767D3xx data sheet (SLVS209) or go to the TPS767D301 TI Product Page. For more detail on the DSP noise and ripple requirements, see the Total Power Requirement and Selecting Voltage Regulators section of the Hardware Design Guidelines for TMS320F28xx and TMS320F28xxx DSCs application report (SPRAAS1). Table 2. Voltage Rail Ripple Voltage Values OUTPUT CURRENT (mA) 1.8-V RAIL VOLTAGE RIPPLE 3.3-V RAIL VOLTAGE RIPPLE (mV) (mV)

1 5

10 5

5 12

10 5

11 50

6 14

100 6

17 200

6 23

300 9

35 400

10 41

4 TMS320F28xx and TMS320F28xxx DSP Power Reference Design SLVA296ACFebruary 2008CRevised April

2008 Submit Documentation Feedback www.ti.com Output Current Table 2. Voltage Rail Ripple Voltage Values (continued) OUTPUT CURRENT (mA) 1.8-V RAIL VOLTAGE RIPPLE 3.3-V RAIL VOLTAGE RIPPLE (mV) (mV)

500 -

53 Output Current Because the overall requirements depend on the specific application, the maximum output current for the power design is higher than the estimated DSP current consumption at full operation (see Table 3). For full details on output currents, see the appropriate DSP data sheet. Table 3. Maximum Output Current MAXIMUM VOLTAGE RAIL CURRENT USED DURING FLASH DSP FAMILY CONSTANT (V) ERASE(Er)/Write(Wr) CURRENT (mA) TMS320F28xxx 1.8

328 See data sheet 3.3

67 TMS320F281x 1.8

230 140 mA 3.3

125 95 mA (Er) /

55 mA (Wr) TMS320F280x 1.8

268 140 mA 3.3

69 95 mA (Er) /

55 mA (Wr) TMS320F28044 1.8

268 140 mA 3.3

57 95 mA (Er) /

55 mA (Wr) Optional Features Power-Save Mode―The TPS62402 can be set to constant-PWM mode or Power-Save mode by connecting the MODE/DATA pin to VIN or GND, respectively. See the TPS62402 data sheet (SLVS681) for more details. Watchdog Timer―The TPS3306-18 has a Watchdog Timer Input (WTI) that can be connected to the DSP. The Watchdog Timer is deactivated if the WTI pin is left open. See the TPS3306-18 data sheet (SLVS290) for additional information. Power-Fail Comparator ― The TPS3306-18 has a Power-Fail Comparator that can be used to monitor voltages other than the nominal supply voltages. The threshold can be set using the power-fail input (PFI), which controls the open-drain, power-fail output (PFO). See the TPS3306-18 data sheet (SLVS290) for more detail. SLVA296ACFebruary 2008CRevised April

2008 TMS320F28xx and TMS320F28xxx DSP Power Reference Design

5 Submit Documentation Feedback Schematic www.ti.com Schematic Bill of Materials Count RefDes Value Description Size Part Number MFR

4 C1, C2,

10 ?F Capacitor, Ceramic, 10V, X5R, 10%

0805 C2012X5R1A106K TDK C4, C5

2 C3, C6 0.1 ?F Capacitor, Ceramic, 25V, X5R, 10%

0603 C1608X5R1E104K TDK

2 L1, L2 2.2 ?H Inductor, SMT, 1.2A,

90 m? 0.118 * 0.118 in LPS3010-222ML Coilcraft

1 R1 100k Resistor, Chip, 1/16W, 1%

0603 Std

1 U1 TPS62402DRC IC, 2.25 MHz Dual Step Down Converter QFN10 TPS62402DRC TI

1 U2 TPS3306-18D IC, Dual Processor Supervisory Circuit with SO8 TPS3306-18D TI Power-fail Modifications for the TMS320F281x and TMS320F28xxx This design can be modified to fit the requirements for the TMS320F281x and TMS320F28xxx. The TPS62402 can be replaced with the TPS62400, which is the adjustable version of the same dual step-down converter. Sequencing requirements can be changed by connecting the enable pin of each converter to the preceding voltage rail. For example, to bring up the 3.3-V rail first, attach the EN2 pin to VIN and the EN1 pin to the 3.3-V rail. The same TPS3306-18 SVS can be used because its voltage threshold is 1.68 V or another SVS can be used as long as the RESET signal is open drain.