Datasheet

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PRINCIPLES OF OPERATION
Functional Principle
Description of the Functional Terminals
Switch-Mode Input/Output Terminals (L1, L2)
Supply Terminal (V
driver
)
mode, the RMS current is
I
OUT
D * D
2
Ǹ
, where D is the duty cycle and its maximum RMS current value is
Internal Supply Decoupling Terminal (V
logic
)
Input Voltage Monitoring Terminal (A
IN
)
Upper:
Lower:
V =2.5V×
(driver)
R1+R2
R1
V =2.3V×
(driver)
R1+R2
R1
.
TPIC74100-Q1
BUCK/BOOST SWITCH-MODE REGULATOR
SLIS125 DECEMBER 2006
The TPIC74100-Q1 is a buck/boost switch-mode regulator that operates in a power-supply concept to ensure a
stable output voltage with input voltage excursions and specified load range.
The device provides an alarm indicator and reset output to interface with systems that require supervisory
function.
The switching regulator offers a clock modulator and a current-mode slew-rate control for the internal switching
transistor (Q1) to minimize EMI.
An internal low-r
DS(on)
switch has a current-limit feature to prevent inadvertent reset when turning on the 5Vg
output.
The external inductor for the switch-mode regulator is connected between terminals L1 and L2. This inductor is
placed close to the terminals to minimize parasitic effects. For stability, an inductor with 20 µ H to 100 µ H should
be used.
The input voltage of the device is connected to the V
driver
terminal. This input line requires a filter capacitor to
minimize noise. A low-ESR aluminum or tantalum input capacitor is recommended. The relevant parameters for
the input capacitor are the voltage rating and RMS current rating. The voltage rating should be approximately
1.5 times the maximum applied voltage for an aluminum capacitor and 2 times for a tantalum capacitor. In buck
reached when D = 50% with I
RMS
= I
OUT
/2. In boost mode, the RMS current is 0.3 × I, where I is the
peak-to-peak ripple current in the inductor. To achieve this, ESR ceramic capacitors are used in parallel with the
aluminum or tantalum capacitors.
The V
logic
terminal is used to decouple the internal power-supply noise by use of a 470-nF capacitor. This
terminal can also be used as an output supply for the logic-level inputs for this device (SCR0, SCR1, ENABLE,
CLP, and 5Vg_ENABLE).
The A
IN
terminal is used to program the threshold voltage for monitoring and detecting undervoltage conditions
on the input supply. A maximum of 40 V may be applied to this terminal and the voltage at this terminal may
exceed the V
(driver)
input voltage without effecting the device operation. The resistor divider network is
programmed to set the undervoltage detection threshold on this terminal (see the application schematic). The
input has a typical hysteresis of 200 mV with a typical upper limit threshold of 2.5 V and a typical lower limit
threshold of 2.3 V. When V
(AIN)
falls below 2.3 V, V
(AOUT)
is asserted low; when V
(AIN)
exceeds 2.5 V, V
(AOUT)
is in
the high-impedance state.
The equations to set the upper and lower thresholds of V
(AIN)
are:
7
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