sc1157 Semtech Corporation, sc1157 Datasheet - Page 4

• Manufacturer Part Number: sc1157
• Description: Programmable Synchronous Dc/dc Controller For Advanced Processors
• Manufacturer: Semtech Corporation

OUTPUT VOLTAGE TABLE
Unless specified: V
T
PARAMETER
Output Voltage
Preliminary - August 7, 2000
NOTE:
(1) All VID codes not specifically listed are invalid and cause shutdown exactly as if the shutdown pin had been
asserted.
THEORY OF OPERATION
The voltage at the VOSENSE pin is applied, through the internal precision resistor feedback chain, to the inverting
input of the error amplifier. The non-inverting input of the error amplifier is supplied with a DC voltage derived by
the DAC from the internal trimmed bandgap voltage reference. The output of the error amplifier is compared to the
triangular output of the internal oscillator to generate a fixed frequency, variable duty cycle pulse train. The internal
oscillator uses an on-chip capacitor and precision trimmed current sources to set the frequency to 100 kHz.
The generated pulse train is gated with the output of the current limit latch and the inhibit signal to produce a drive
signal for the upper FET. It is also inverted to produce a drive signal for the lower FET. These FET drive signals
are modified by the “shoot-through control” circuitry so that the top FET turn-on is delayed until the bottom FET has
turned off, and visa-versa.
The current limit latch is set (ending the upper FET drive pulse early) if the current limit comparator indicates an
overcurrent condition. The latch is reset at the start of each oscillator period.
© 2000 SEMTECH CORP.
J
= 0°C to 85°C
(1)
CC
= 4.75V to 5.25V; GND = PGND = 0V; FB = V
I
(Figure 1)
O
= 2A in Application Circuit
CONDITIONS
PROGRAMMABLE SYNCHRONOUS DC/DC
CONTROLLER FOR ADVANCED PROCESSORS
652 MITCHELL ROAD NEWBURY PARK CA 91320
3210
1111
1110
1101
1100
1011
1010
1001
1000
0111
0110
0101
0100
0011
0010
0001
0000
VID
O
; 0mV < (CS(+) - CS(-)) < 60mV;
1.337
1.386
1.436
1.485
1.535
1.584
1.634
1.683
1.733
1.782
1.832
1.881
1.931
1.980
2.030
1.287
MIN
1.300
1.350
1.400
1.450
1.500
1.550
1.600
1.650
1.700
1.750
1.800
1.850
1.900
1.950
2.000
2.050
TYP
1.313
1.364
1.414
1.465
1.515
1.566
1.616
1.667
1.717
1.768
1.818
1.869
1.919
1.970
2.020
2.070
MAX
SC1157
UNITS
V
4