LTC1142HVCG Linear Technology, LTC1142HVCG Datasheet - Page 8

• Manufacturer Part Number: LTC1142HVCG
• Description: IC SW REG STEP-DOWN DUAL 28-SSOP
• Manufacturer: Linear Technology
• Type: Step-Down (Buck)r

Specifications of LTC1142HVCG

• Internal Switch(s): No
• Synchronous Rectifier: Yes
• Number Of Outputs: 2
• Voltage - Output: 3.3V, 5V
• Current - Output: 50mA
• Frequency - Switching: 250kHz
• Voltage - Input: 3.5 ~ 18 V
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 28-SSOP
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Power - Output: -

LTC1142/LTC1142L/LTC1142HV
Only one regulator block shown. Pin numbers are for 3.3V (5V) sections for LTC1142/LTC1142HV,
and V
OPERATIO
The LTC1142 series consists of two individual regulator
blocks, each using current mode, constant off-time archi-
tectures to synchronously switch an external pair of
complementary power MOSFETs. The two regulators are
internally set to provide output voltages of 3.3V and 5V for
the LTC1142. The LTC1142HV-ADJ/LTC1142L-ADJ are
configured to provide two user selectable output voltages,
each set by external resistor dividers. Operating fre-
quency is individually set on each section by the external
capacitors at C
The output voltage is sensed by an internal voltage divider
connected to Sense
divider returned to V
voltage comparator V and a gain block G compare the
divided output voltage with a reference voltage of 1.25V.
To optimize efficiency, the LTC1142 series automatically
switches between two modes of operation, Burst Mode
and continuous mode. The voltage comparator is the
primary control element when the device is in Burst Mode
operation, while the gain block controls the output voltage
in continuous mode.
FU CTIO AL DIAGRA
8
U
OUT1
LTC1142-ADJ
(V
OUT2
3(17)
2(16)
SLEEP
U
) for LTC1142L-ADJ/LTC1142HV-ADJ.
T
S
, Pins 11 and 25.
–
+
U
PIN NUMBERS
FOR LTC1142L-ADJ
LTC1142HV-ADJ
PIN NUMBERS FOR
LTC1142, LTC1142HV
–
V
, Pin 28 (14) (LTC1142) or external
TH2
FB
Refer to Functional Diagram
25(11)
, Pin 2 (16) (LTC1142-ADJ). A
C
T
V
TH1
W
+
Q
–
OFF-TIME
CONTROL
T
R
S
V
SENSE
IN
–
LTC1142L-ADJ, LTC1142HV-ADJ: 5(19)
C
During the switch “ON” cycle in continuous mode, current
comparator C monitors the voltage between Pins 1 (15)
and 28 (14) connected across an external shunt in series
with the inductor. When the voltage across the shunt
reaches its threshold value, the PDrive output is switched
to V
capacitor connected to Pin 25 (11) is now allowed to
discharge at a rate determined by the off-time controller.
The discharge current is made proportional to the output
voltage [measured by Pin 28 (14)] to model the inductor
current, which decays at a rate that is also proportional to
the output voltage. While the timing capacitor is discharg-
ing, the NDrive output goes to V
MOSFET.
When the voltage on the timing capacitor has discharged
past V
causes the NDrive output to go low (turning off the
N-channel MOSFET) and the PDrive output to also go low
(turning the P-channel MOSFET back on). The cycle then
repeats.
–
LTC1142HV-ADJ
+
LTC1142L-ADJ
6(20)
4(18)
27(13)
24(10)
SHDN
23(9)
2(16)
3(17)
IN
25mV TO 150mV
I
TH
, turning off the P-channel MOSFET. The timing
TH1
–
PGND
NDRIVE
V
PDRIVE
, comparator T trips, setting the flip-flop. This
IN
13k
+
SGND
3(17)
V
G
–
–
+
+
REFERENCE
LTC1142HV-ADJ
LTC1142L-ADJ
SENSE
4(18)
1(15)
1.25V
V
LTC1142HV-ADJ
IN
LTC1142L-ADJ
OS
+
, turning on the N-channel
NC/ADJ
2(16)
INTV
26(12)
CC
SENSE
28(14)
100k
–
1142 BD
5pF