Nice selection. The sky one (in the 3.3 fixed voltage option) seems to need less parts. According to efficiency curves, with the near 3v voltage of a CR2032 it should handle very well.
On Fri, Sep 13, 2013 at 5:56 PM, Werner Almesberger <[email protected]>wrote: > 1) The converter chip > > Requirements: > - can convert 1.8-3.0 V to 3.3 V, > - Imax about 200 mA if we have a partcularly nasty memory card > - enable/disable input > - no center pad (to make manual soldering easier) > > The usual Digi-Key search: > > Product Index > Integrated Circuits (ICs) > > PMIC - Voltage Regulators - DC DC Switching Regulators -> 19092 > Mounting Type: SMT -> 17,593 > In stock -> 7,022 > Packaging: Cut Tape/Bulk/Tray/Tube -> 3,739 > Voltage - Input: min <= 1.8 V -> 498 > Current - Output: >= 200 mA -> 262 > Number of Outputs: 1 -> 251 > Synchronous Rectifier: Yes -> 163 > Voltage - Output: min <= 3.3 V -> 142 > Type: Step-Up (or Step-Up and Step-Down) -> 116 > Voltage - Output: eliminate max < 3.3 V -> 107 > Supplier Device Package: < 10 pins -> 50 > > Order by Unit Price @ 100: > 0.39 Skyworks AAT1217ICA-1.2-T1 TSOT-23-6, up, adj, 500 mA, 1.2 MHz > 0.39 Skyworks AAT1217ICA-3.3-T1 TSOT-23-6, up, 3.3 V, 500 mA, 1.2 > MHz > 0.55 TI TLV61220DBVR SOT-23-6, up, adj, 400 mA, ? > 0.67 TI TPS61220DCKR SOT-363, up, adj, 200 mA, 2 MHz > 0.77 TI TPS61221DCKT SOT-363, up, 3.3 V, 200 mA, 2 MHz > 0.77 TI TPS61220DCKT SOT-363, up, adj, 200 mA, 2 MHz > 0.79 TI TPS61071DDCR TSOT-23-6, up, adj, 600 mA, 1.2 MHz > ... more TPS6107xDDCR ... > ... skip WDFN ... > ... skip 8-VSSOP ... > 0.79 TI LMR61428XMM/NOPB 8-VSSOP, up, adj, 2.85 A, 2 MHz > 1.02 Exar SP6641BEK-L-3-3 SOT-23-5, up, 3.3 V, 500 mA, ? > 1.10 TI TLV61225DCKT SOT-363, up, 3.3 V, 200 mA, 2 MHz > 1.13 ON NCP1421DMR2G 8-TSSOP, up, adj, 600 mA, 1.2 MHz > 1.13 ON NCP1410DMR2G 8-TSSOP, up, adj, 200 mA, 0.6 MHz > > AAT1217ICA-3.3-T1 2.9 x 2.2 mm EN, 2 x 4.7 uF, 4.7 uH > TLV61220DBVR ? EN, 2 x 10 uF, 4.7 uH > TPS61221DCKT 2 x 2 mm EN, 2 x 10 uF, 4.7 uH > TPS61071DDCR ? EN, 2 x 10 uF, 4.7 uH > LMR61428XMM external diode > SP6641BEK-L-3-3 **huge** caps > TLV61225DCKT no data sheet > NCP1421DMR2G complex external circuit > > Selecting parts with the same package and where the package isn't > an extreme size: > > Pin assignment, starting at 1: > > AAT1217ICA SW, GND, (FB), nSHDN, VOUT, VIN > TLV61220DBVR SW, GND, EN, FB, VOUT, VBAT > > So they're similar but not the same. There are probably a number of > very similar parts on the Chinese market, so 3rd sources and such > shouldn't be a problem. > > -> design for AAT1217ICA series, > leave room for voltage-setting resistors (BOM option), > use 10 uF caps, > allow for modification for TLV61220DBVR > > > 2) The inductor > > according to the formulas on page 8 of > http://www.skyworksinc.com/uploads/documents/AAT1217_202050B.pdf > > Vin = 1.8 V > Vout = 3.3 V > Iout = 200 mA > Fsw = 1.2 MHz > L = 4.7 uH > n = 0.7 > > Idc = Iout*Vout/(n*Vin) = 0.524 > dIl = Vin*(Vout-Vin)/(L*Fsw*Vout) = 0.145 > > Ipeak = Idc + dIl/2 > Ipeak = 0.6 A > > Let's go to Digi-Key: > > Product Index > Inductors, Coils, Chokes > Fixed Inductors -> 102964 > In stock -> 38020 > Shielding: Shielded -> 15519 > Packaging: Bulk / Cut Tape / Tray -> 5835 > Mounting Type: SMT -> 5581 > Current Rating: >= 590 mA -> 4295 > Current Rating: <= 10 A -> 3848 > Inductance: 4.5 uH - 4.9 uH -> 298 > Package / Case: 1008 (2520 Metric) -> 14 > > Order by price @100 units: > 0.11900 Samsung CIG22L4R7MNE 4.7 uH, 1.1 A, 20%, 110 mOhm, H > 2.5 mm > 0.14630 Bourns CVH252009-4R7M 4.7 uH, 1.1 A, 20%, 110 mOhm, H > 0.9 mm > 0.16650 Sumida 252010CDMCDS-4R7MC 4.7 uH, 1.4 A, 20%, 240 mOhm, H > 1.0 mm > ... > > All three look quite suitable. > > - Werner > > _______________________________________________ > Qi Hardware Discussion List > Mail to list (members only): [email protected] > Subscribe or Unsubscribe: > http://lists.en.qi-hardware.com/mailman/listinfo/discussion > -- Felix
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