MC33560DW データシートの表示（PDF） - ON Semiconductor
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MC33560DW Datasheet PDF : 26 Pages
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MC33560
VBAT
Rectifier Switch
L1
PWN
FEED
BACK CLOCK OFF
STOP
Low Side
Switch
RECTIFIER
CONTROL
ON /OFF
ILIMCOMP
−
+
120 mV
ON /OFF
CRDGND
2W
PGND
0.5
W
Internal
resistors
ILIM
RLIM (external)
DIGITAL
FILTER
LOGIC
AND
COUNTER
OVER TEMP
DETECTION
− UNDER VOLTAGE
+
DETECTOR
VBATOK
CONVERTER
FAULT +
ERROR
AMP.−
VREF
ON /OFF
CRDVCC
Active pull−down
switch
ON /OFF
3V/5V
CRDGND
Figure 22. DC−DC Converter Functional Block
The overcurrent and undervoltage protection features are
complementary, and will shut the circuit off either if the
overcurrent is high enough to bring the CRDVCC output
below the preset threshold, either after 160 ms (typ.)
In addition, the DC−DC converter will be allowed to start
only if the battery supply voltage is high enough to allow
normal operation (1.8 V).
The undervoltage comparator has a hysteresis and a delay
of typically 20 ms to ensure stable operation. The current
detector is a comparator associated with two resistors: one
2.0 W attached to PGND and usually connected to analog
ground, and a 0.5 W attached to ILIM, usually connected to
ground through an external resistor to adjust the maximum
peak current. The voltage developed across this resistor
network is then compared to a 120 mV (typical) reference
voltage, and the comparator output performs a
cycle−by−cycle peak current limitation by switching off the
low side transistor when the voltage exceeds 120 mV.
The internal ILIMCOMP signal is monitored to stop the
converter if current limitation is continuously detected
during 160 ms (typical). This allows normal operation with
high filtering capacitance and low peak current, even at
converter startup. As a result, a short circuit to ground on the
card connector or a continuous overcurrent is reported by
RDYMOD 160 ms (typical) after powerup.
Unexpected Card Extraction: The MC33560 detects
card extraction and runs a powerdown sequence if card
power is still on when extraction occurs. An active pulldown
switch clamps CRDVCC to GND within 150 ms (max) after
extraction is detected. The external capacitors will then be
discharged. With typical capacitor values of 10 mF and 47 nF
as indicated in the application schematic, the time needed to
discharge CRDVCC to a voltage below 0.4 V can be
estimated to less than 750 ms. The total time aftercard
extraction detection until CRDVCC reaches 0.4 V is then
estimated to 900 ms (maximum). All smartcard connector
contacts will be deactivated before CRDVCC deactivation.
This ensures that no electrical damage will be caused to the
smartcard under abnormal extraction conditions.
3.0 V/5.0 V Programming: It is possible to set the card
supply voltage to 3.0 V or 5.0 V at any time, before DC−DC
converter start, or during converter operation. When
switching from 3.0 V to 5.0 V, a 160 ms (typical) delay
blanks the undervoltage fault detection to allow filter
capacitor charging.
PWM: The free−running integrated oscillator has two
working modes:
Variable on−state and fixed frequency (typically 120 KHz)
for average to heavy loads.
Variable on−state and variable frequency for light loads.
The frequency can be as low as a few kHz if no load is
connected to CRDVCC.
The charging current of the timing capacitor is related to
the VBAT supply voltage, to allow better line regulation, and
to increase stability.
Filtering Capacitor: A high value allows efficient
filtering of card current spikes. Low values allow low startup
charging current. Care must be taken not to combine low
capacitor value with high current limiting, as this can
generate high ripple. Usual values range from 4.7 mF to
47 mF, depending on current limiting.
Selecting the External Components L1 and RLIM:
The choice of inductor L1 and resistor R4 is made by using
Figure 8 (5.0 V card) and/or Figure 9 (3.0 V card) on page 8:
http://onsemi.com
15
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