APE3312GN3 Advanced Power Electronics Corp., APE3312GN3 Datasheet - Page 14

• Manufacturer Part Number: APE3312GN3
• Manufacturer: Advanced Power Electronics Corp.

Specifications of APE3312GN3

• Vin(min): 3
• Vin(max): 28
• Vout(min): 0.75
• Vout(max): 5.5
• Iout(max): 8
• Power Good: ?
• Otp: ?
• Ocp: ?
• Ovp: ?
• Package: DFN 3x3-10L

DETAIL DESCRIPTION
The APE3312 synchronous buck controller is designed for low-voltage power supplies for notebook PC
applications. The APE3312 control scheme is a constant-on-time, pseudo-fixed frequency, current-mode
PWM controller and specifically designed for leading fast load transient while maintaining a relative constant
switching frequency and operating over a wide range of input voltage. This architecture depends on the ESR
of output capacitor; the output ripple voltage across the ESR provides the PWM ramp signal,
need for a current sense resistor.
pulse width is inversely proportional to input voltage and proportional to output voltage. Another one-shot sets
a minimum off-time (400ns typ.). The on-time one-shot is triggered if the error comparator is low.
+5V Bias Input
The APE3312 requires an external +5V bias supply in addition to the battery voltage. The external bias supply
is needed to supply the PWM control circuitry and gate drivers. The +5V input can be generated by an
external linear regulator, if stand-alone capability is needed. The 5V bias supply must be power up after to the
battery supply (VIN) is present to ensure startup well.
On-Time One-Shot (T
The core of pseudo fixed frequency PWM is the one-shot that sets the on-time of high-side switch for the
controller. This low jitter, adjustable one-shot includes circuitry that varies the on-time in response to VIN and
output voltage. The on-time is disproportional to the input voltage, and proportional to the output voltage, so
that the duty ratio is kept as VOUT/VIN theoretically.
Switch frequency / Mode selection
The switching frequency is selectable from four preset values by a resistor connected to RF as shown in
Table 1. Leave the RF pin open to set the lowest switching frequency, 290 kHz.
The APE3312 operates with PWM-only or auto-skip mode by connecting R
multi-function. Pull RF pin low via R
R
RF
to force PWM-only mode.
Advanced Power
Electronics Corp.
ON
)
Resistance (kΩ)
The high-side switch on-time is determined by an internal one-shot which
470
200
100
RF
39
to set the APE3312 operates in auto-skip mode. Pull RF pin high via
Table1. R
Switching Frequency (kHz)
RF
vs. f
SW
290
340
380
430
RF
high or low to provide
APE3312
eliminating the
14