L6910GTR ,Adjustable step down controller with synchronous rectificationElectrical Characteristics (V = 12V, T =25°C unless otherwise specified)cc JSymbol Parameter Test C ..
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L6910G-L6910GTR
Adjustable step down controller with synchronous rectification
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L6910GMay 2005
FEATURES OPERATING SUPPLY VOLTAGE FROM 5V
TO 12V BUSES UP TO 1.3A GATE CURRENT CAPABILITY ADJUSTABLE OUTPUT VOLTAGE N-INVERTING E/A INPUT AVAILABLE 0.9V ±1.5% VOLTAGE REFERENCE VOLTAGE MODE PWM CONTROL VERY FAST LOAD TRANSIENT RESPONSE 0% TO 100% DUTY CYCLE POWER GOOD OUTPUT OVERVOLTAGE PROTECTION HICCUP OVERCURRENT PROTECTION 200kHz INTERNAL OSCILLATOR OSCILLATOR EXTERNALLY ADJUSTABLE
FROM 50kHz TO 1MHz SOFT START AND INHIBIT PACKAGE: SO-16
APPLICATIONS SUPPLY FOR MEMORIES AND TERMI-
NATIONS COMPUTER ADD-ON CARDS LOW VOLTAGE DISTRIBUTED DC-DC MAG-AMP REPLACEMENT
DESCRIPTIONThe device is a pwm controller for high performance
dc-dc conversion from 3.3V, 5V and 12V buses.
The output voltage is adjustable down to 0.9V;
higher voltages can be obtained with an external
voltage divider.
High peak current gate drivers provide for fast switch-
ing to the external power section, and the output
current can be in excess of 20A.
The device assures protections against load overcur-
rent and overvoltage.
An internal crowbar is also provided turning on the
low side mosfet as long as the over-voltage is detect-
ed. In case of over-current detection, the soft start ca-
pacitor is discharged and the system works in
HICCUP mode.
ADJUSTABLE STEP DOWN CONTROLLER
WITH SYNCHRONOUS RECTIFICATION
Figure 2. Block DiagramRev. 1
L6910G
Table 2. Absolute Maximum Ratings
Table 3. Thermal Data(*) Device soldered on 1 S2P PC board
Figure 3. Pins Connection (Top view)
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L6910G
Table 4. Pins Function
L6910G
Table 5. Electrical Characteristics (Vcc = 12V, TJ =25°C unless otherwise specified)
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L6910G DEVICE DESCRIPTIONThe device is an integrated circuit realized in BCD technology. The controller provides complete con-
trol logic and protection for a high performance step-down DC-DC converter. It is designed to drive N
Channel Mosfets in a synchronous-rectified buck topology. The output voltage of the converter can be
precisely regulated down to 900mV with a maximum tolerance of ±1.5% when the internal reference is
used (simply connecting together EAREF and VREF pins). The device allows also using an external
reference (0.9V to 3V) for the regulation. The device provides voltage-mode control with fast transient
response. It includes a 200kHz free-running oscillator that is adjustable from 50kHz to 1MHz. The er-
ror amplifier features a 10MHz gain-bandwidth product and 10V/µs slew rate that permits to realize
high converter bandwidth for fast transient performance. The PWM duty cycle can range from 0% to
100%. The device protects against over-current conditions entering in HICCUP mode. The device
monitors the current by using the rDS(ON) of the upper MOSFET(s) that eliminates the need for a cur-
rent sensing resistor. The device is available in SO16 narrow package.
4.1 OscillatorThe switching frequency is internally fixed to 200kHz. The internal oscillator generates the triangular waveform
for the PWM charging and discharging with a constant current an internal capacitor. The current delivered to the
oscillator is typically 50µA (Fsw = 200KHz) and may be varied using an external resistor (RT) connected between
OSC pin and GND or VCC. Since the OSC pin is maintained at fixed voltage (typ. 1.235V), the frequency is var-
ied proportionally to the current sunk (forced) from (into) the pin.
In particular connecting RT vs. GND the frequency is increased (current is sunk from the pin), according to the
following relationship:
Connecting RT to VCC = 12V or to VCC = 5V the frequency is reduced (current is forced into the pin), according
to the following relationships:
VCC = 12V
VCC = 5V
Switching frequency variation vs. RT are repeated in Fig. 4.
Note that forcing a 50µA current into this pin, the device stops switching because no current is delivered to the
oscillator.
Figure 4. OSC,RT 200KHz 4.94 106⋅T KΩ()-------------------------+= OSC,RT 200KHz 4.306 107⋅T KΩ()------------- ----------------–= OSC,RT 200KHz 15 106⋅T KΩ()---------------------–=
