NCN6004A
http://onsemi.com
21
POWER MANAGEMENT
The main purpose of the power management is to provides
the necessary output voltages to drive the 1.80 V, 3.0 V or
5.0 V smart card types. On top of that, the DC/DC converter
efficiency must absorb a minimum current on the V
bat
supply.
Beside the power conversion, in the Stand by mode
(PWR_ON = L), the power management provides energy to
the card detection circuit only. All the card interface pins are
forced to ground potential, saving as much current as
possible out of the battery supply.
In the event of a power up request coming from the
external MPU (CARD_SEL =H/L, PWR_ON = H, CS = L),
the power manager starts the DC/DC converter related to the
selected interface section.
When the selected section (either CRD_VCC_A or
CRD_VCC_B) voltage reaches the programmed value
(1.8 V, 3.0 V or 5.0 V), the circuit activates the card signals
according to the following sequence:
CRD_VCC_x → CRD_IO_x → CRD_C4_x → CRD_C8_x
→ CRD_CLK_x → CRD_RST_x
The logic level of the data lines are asserted High or Low,
depending upon the state forced by the external MPU, when
the start−up sequence is completed. Under no situation the
NCN6004A shall automatically launch a smart card ATR
sequence.
At the end of the transaction, asserted by the MPU
(CARD_SEL = H/L, PWR_ON = L, CS = L), or under a card
extraction, the ISO7816−3 power down sequence takes
place:
CRD_RST_x → CRD_CLK_x → CRD_C4_x →
CRD_C8_x → CRD_IO_x → CRD_VCC_x
When CS = H, the bi−directional I/O lines (pins 9 and 19)
are forced into the High impedance mode to avoid signal
collision with any data coming from the external MPU.
OUTPUT VOLTAGE PROGRAMMING
The internal logic provides a reliable circuit to activate
any of the DC/DC converters safely. In particular, the Turn
On/Turn Off of these converters is edge sensitive and
controlled by the rising/falling edges of the PWR_ON signal
applied with Chip Select pin Low. The CARD_SEL signal
is used to select either CRD_VCC_A or CRD_VCC_B as
defined by the functions programming in Table 2.
PWR_ON
CRD_VCC Rise Time
CRD_VCC No Change
CRD_VCC_A PWR DOWN
VCCtoff
CARD_SEL
CRD_VCC_A
CRD_VCC_B
SET
RESET
VCCton
VCCton
see note
Note : minimum 1 ms delay before to send a power Off command to the same
selected output is recommended.
Figure 12. Card Power Supply Controls
CS
Although it is possible to change the output voltage
straightly from 5.0 V to 1.80 V, care must be observed as the
stabilization time will be relatively long if no current is
absorbed from the related output pin.
According to the typical sequence depicted, it is not
possible to program simultaneously the two DC/DC
converters, but two separate sequences must take place. On
top of that, since the circuit is edge sensitive, the PWR_ON
signal must present such a transient when a given state is
expected for the converter. The PWR_ON and CS timings
definitions are given in Figure 13.
