SP6134 Datasheet, PDF (5/14 Pages) Sipex Corporation – Dual Supply Synchronous Buck Controller

FUNCTIONAL DIAGRAM
5 COMP
100% Protection Logic
VCC
PWM LOOP
PULSES CLR
COUNT 20
CLOCK
CLK
FAULT
VFB
VCC
Gm ERROR AMPLIFIER
VFBINT
VCC
Gm
VPOS
FAULT
10 µA
SS 7
SOFTSTART INPUT
POS REF
FAULT
FAULT
RESET
DOMINANT
R
Q
S
QPWM
RAMP = 1.1V
0.4 V
600 kHZ
CLK
CLOCK PULSE GENERATOR
V_CC 1
REFERENCE
CORE
0.8V
REF OK
1.7 V
SS
1.7 V
ASYNC. STARTUP
COMPARATOR
SYNCHRONOUS
DRIVER
GL HOLD OFF
10 BST
9 GH
8 SWN
2 GL
3 GND
145 ˚C ON
135 ˚C OFF
THERMAL
SHUTDOWN
VPOS
VFBINT
0.25 V
+-
SHORT CIRCUIT
DETECTION
+
-
SET
DOMINANT
S
Q
R
HICCUP FAULT
REF OK
VCC
+
4.25 V ON
4.05 V OFF -
VCC UVLO
POWER FAULT
FAULT
+
2.50 VON
2.20 V OFF
-
VIN UVLO
CLK
COUNTER _{200ms Delay}
6
UVIN
CLR
REF OK
THERMAL AND SHORT CIRCUIT PROTECTION
UVLO COMPARATORS
THEORY OF OPERATION
General Overview
The SP6134 is a fixed frequency, voltage mode,
synchronous PWM controller optimized for high
efficiency. The part has been designed to be
especially attractive for split plane applications
utilizing 5V to power the controller and 3V to
12V for step down conversion.
The heart of the SP6134 is a wide bandwidth
transconductance amplifier designed to accom-
modate Type II and Type III compensation
schemes. A precision 0.8V reference present on
the positive terminal of the error amplifier per-
mits the programming of the output voltage
down to 0.8V via the V_FB pin. The output of the
error amplifier, COMP, compared to a 1.1V
peak-to-peak ramp is responsible for trailing
edge PWM control. This voltage ramp and PWM
control logic are governed by the internal oscil-
lator that accurately sets the PWM frequency to
600kHz.
The SP6134 contains two unique control fea-
tures that are very powerful in distributed appli-
cations. First, asynchronous driver control is
enabled during start up to prohibit the low side
NFET from pulling down the output until the
high side NFET has attempted to turn on. Sec-
ond, a 100% duty cycle timeout ensures that the
low side NFET is periodically enhanced during
extended periods at 100% duty cycle. This guar-
antees the synchronized refreshing of the BST
capacitor during very large duty ratios.
The SP6134 also contains a number of valuable
protection features. A programmable input (V_IN)
UVLO allows a user to set the exact value at
which the conversion voltage is at a safe point to
begin down conversion, and an internal V_CC
UVLO ensures that the controller itself has
enough voltage to properly operate. Other pro-
Date: 5/25/04
SP6134 Dual Supply, Synchronous Buck Controller
5
© Copyright 2004 Sipex Corporation