MAX14500 Datasheet, PDF (32/41 Pages) Maxim Integrated Products – Hi-Speed USB-to-SD Card Readers with Bypass

Hi-Speed USB-to-SD Card
Readers with Bypass
Power-Supply Modes
The MAX14500–MAX14503 have four power-supply
inputs (Table 6). Bypass V_CC, V_IO, V_SD, and V_TM with
high-frequency, surface-mount ceramic capacitors as
close as possible to the supply pins.
Table 6. Power-Supply Inputs
SUPPLY
FUNCTION
V_TM
USB transceiver and USB
switch power
V_CC
Digital core 1.8V LDO
V_SD
SD card level translator and SD
switches
V_IO
Host microprocessor level
translator
RANGE (V)
+2.91 to +3.4
+2.1 to +3.6
+2.0 to +3.6
+1.5 to +3.6
Power-supply inputs:
1) V_TM USB Transceiver Power. This supply powers the
USB analog switches, PLL subsystem, and the USB
2.0 transceiver. This regulator can be internal to a
power-management IC, or it can be discrete and is
recommended to be powered from USB VBUS. This
supply must be present when the MAX14500–
MAX14503 are used in Card Reader mode to pass
USB signals in Pass Thru mode.
2) V_CC Digital Logic Power. This supply powers the
digital logic/internal microcontroller/flash memory.
There is an internal +1.8V LDO (CLDO) with shut-
down controlled by the state of the MODE input and
internal logic.
3) V_SD SD Card Power. This supply powers the SD
card level translator and SD card switches. V_SD
needs to be present to pass SD signals in Pass Thru
mode.
4) V_IO Host Interface Power. This supply powers the
digital I/O and I²C interface.
Power modes:
1) Idle. Only V_IO is required to be present. I²C registers
can be updated, but no operation is possible.
2) Pass Thru Mode. V_IO needs to be present so the
voltage level at MODE can be detected. To allow
USB pass thru, the V_TM supply needs to be present.
To allow SD pass thru, V_SD supply needs to be pre-
sent. Each supply is independent from the others
and no power-supply sequencing is required.
3) Card Reader Mode. All supplies are needed. When
the card reader is actively transferring data, this mode
draws the most current, mainly from V_CC and V_TM.
Layout Considerations
The MAX14500–MAX14503 support Hi-Speed USB and
requires careful PCB layout. Use controlled-impedance
matched traces of equal lengths to the USB connector
with no discontinuities and a minimum number of
feedthroughs. All SD traces (CLK, CMD, DAT_) should
be of equal lengths and as short as possible.
Choosing Pullup Resistors
I²C requires pullup resistors to provide a logic-high level
to data and clock lines. There are tradeoffs between
power dissipation and speed, and a compromise must
be made in choosing pullup resistor values. Every
device connected to the bus introduces some capaci-
tance, even when the device is not in operation. I²C
specifies 300ns rise time to go from low to high (30% to
70%) for fast mode, which is defined for data rates up to
400kbps. To meet the rise time requirement, choose
pullup resistors so the rise time (t_R) is less than 300ns
where t_R ≈ 0.85 x R_PULLUP x C_BUS. If the transition time
becomes too slow, the setup and hold times may not be
met and waveforms may not be recognized.
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